Foundation Release Notes for OS X v10.9

Document Generated: 2013-06-05 11:58:10 -0700

OS X Release Notes Copyright © 2013 Apple Inc. All Rights Reserved.

OS X 10.9 Release Notes for Cocoa Foundation Framework

The Foundation Framework is a library of Objective-C classes that provide the infrastructure for object-based applications without graphical user interfaces. It is available on OS X and iOS.

You can find release notes for the Application Kit as well as some notes on general backward compatibility issues, version handling, etc, in Application Kit Release Notes for OS X v10.8.

These notes cover many, but by no means all of the changes in the Foundation Kit in OS X 10.9 in the WWDC 2013 seed. These notes as well as the underlying changes they refer to are subject to further change before final release of 10.9.

Some of the major topics covered in this document:

NSXPCConnection

In OS X 10.8 Mountain Lion, if a programmer error caused an exception when a message is received on a connection, the message would be dropped and no further action would be taken. As of OS X 10.9, NSXPCConnection will also automatically invalidate the connection. This ensures that the error handler will be invoked on the calling side with a ‘connection interrupted’ or ‘connection invalidated’ error.

The CPU and memory performance of sending large amounts of data over an NSXPCConnection is significantly increased.

NSXPCConnection will now clear the invalidation handler, interruption handler, and exported object after the connection is invalidated. This helps prevent accidental retain cycles, for example when an invalidation handler block captures the NSXPCConnection instance. NSXPCConnection will also stop retaining any additional exported objects.

NSKeyedArchiver

In previous releases, archiving a string with the exact contents "$null" would cause it to be unarchived as a nil object. Archives with this string created on OS X 10.9 will unarchive correctly on OS X 10.9 and previous releases.

NSKeyedArchiver supports the NSSecureCoding feature added in OS X 10.8 Mountain Lion. The support is available on OS X 10.8 Mountain Lion and later. To use secure coding, create the NSKeyedUnarchiver or NSKeyedArchiver instance and use the new method. This code sample assumes ARC is enabled.

NSString *myString = @"Hello world";
NSMutableData *data = [NSMutableData data];
NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
[archiver setRequiresSecureCoding:YES];
[archiver encodeObject:myString forKey:@"MyKey"];
[archiver finishEncoding];
 
// ...
 
NSData *dataToUnarchive = ...;
NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:dataToUnarchive];
[unarchiver setRequiresSecureCoding:YES];
NSString *decodedString = [unarchiver decodeObjectOfClass:[NSString class] forKey:@"MyKey"];

If the class of the decoded object is not an NSString or NSString subclass, then the decodeObjectOfClass:forKey: method will thrown an exception.

In OS X 10.9, Foundation exports a new key: NSKeyedArchiveRootObjectKey. This is the root key used for archives created with the existing NSKeyedArchiver method +archivedDataWithRootObject: on all previous releases.

NSBundle

Although the documentation allows NSBundle and CFBundle to insert new keys in a bundle’s Info.plist, doing so resulted in a common crash when the Info.plist dictionary was read on one thread and modified on another. NSBundle and CFBundle will no longer set any additional keys in the Info.plist dictionary, and applications are highly discouraged from attempting to modify the Info.plist dictionary returned from the -infoDictionary method.

NSOperation and NSOperationQueue

The performance of -addOperationWithBlock:, -addOperation:, starting execution of operations, and starting execution of completion blocks is significantly faster.

NSUserNotification

Calling -removeDeliveredNotification: and -removeAllDeliveredNotifications: will now remove notifications that are displayed.

A new property on NSUserNotification, -identifier, can be used to uniquely identify an individual notification even across separate launches of an application. If a notification is delivered with the same identifier as an existing notification, it will replace the preexisting notification. This can be used to update existing notifications.

NSUserNotification has a new property to specify the image shown in the content of a notification.

NSUserNotification allows for a ‘quick reply.’ The property responsePlaceholder can be used to set a placeholder string and the response can be retrieved from the response property.

App Nap

App Nap is a new feature in OS X 10.9 which focuses system resources like CPU, I/O, and battery energy on the most important work done for the user. The system uses heuristics to determine when an application is doing important work, and when the work it is doing is not critical. These heuristics include (but are not limited to): visibility on screen, drawing activity, event processing, audio playback, foreground vs background, and application type.

When an application enters app nap mode, the system applies up to three kinds of effects: CPU priority lowering, I/O priority lowering, and timer throttling. CPU priority lowering will make an application lower priority than other apps, but not as low as most system daemons. I/O priority lowering will allow I/O to proceed as fast as possible, but allows high priority I/O to go first. This is designed to improve responsiveness in foreground applications that the user is actively interacting with. Timer throttling will reduce the frequency of most kinds of timers in an application. These combined effects provide a significant increase in battery life when an application is performing frequent unnecessary work.

The greatest benefit to the user comes when every application on their system is doing as little work as possible. Therefore, App Nap is an opt-out feature. The user can opt an application out of App Nap manually with a checkbox in the Finder “Get Info...” pane. Developers can temporarily opt an application out by bracketing user-initiated activities with new NSProcessInfo API. Please consider the power usage of your application before opting out of App Nap.

App Nap - User Activities

Applications can help improve the result of the App Nap heuristics by using new API on NSProcessInfo to distinguish user-initiated activities from background or other maintenance work. This API is called automatically by AppKit for user event handling. You should call it when your application begins long-running or asynchronous work.

The new API has two forms. The first form is a begin/end pairing. Call -[NSProcessInfo beginActivityWithOptions:reason:] when your application begins a user initiated activity. The returned object should then passed into -[NSProcessInfo endActivity:] when the activity is finished.

The second form is block-based: -[NSProcessInfo performActivityWithOptions:reason:block:]. With this API, you specify the kind of activity and do the work inside the block. The method will run the block synchronously and automatically begin and end the activity around the block.

The options parameter describes the kind of activity your application is performing. If the work is user initiated, use NSActivityUserInitiated. If the work is background or other maintenance work then use NSActivityBackground. The options can also be used to prevent the system from entering idle system sleep or idle display sleep, with the NSActivityIdleSystemSleepDisabled and NSActivityIdleDisplaySleepDisabled constants. If your app is performing user initiated work that should not prevent the system from idle sleeping, then use NSActivityUserInitiated. You should be careful to choose the right kind of activity any time you use the new API. Preventing the computer from idling and going to sleep may result in an empty battery.

User initiated activities should be limited to work explicitly started by the user. Examples include exporting files or recording audio. Application-initiated activities like performing maintenance should either not use this API or use the NSActivityBackground type. There is new API in XPC for performing regular maintenance activities at more appropriate times (like when connected to A/C power). See <xpc/activity.h>.

App Nap - Debugging

There are many new tools available on the system to investigate the root cause of unexpected battery drain. Xcode now includes a view of the energy usage when running your application. Activity Monitor includes a new column that shows if your app is in App Nap or not, plus a synthesized “power score” which indicates the overall power usage of your app. The battery menu extra will now report apps using an excessive amount of power. The new command line tool timerfires (“man timerfires” for more information) can be used to investigate what timers your application has scheduled.

You should strive to have a power score of 0.0 and 0 idle wake ups. Remember that even a small amount of CPU usage can have a significant effect on battery life.

Timer Tolerance

It is now possible to inform the system of the potential “tolerance” for NSTimer or CFRunLoopTimerRef objects. The tolerance is an allowable delay after the scheduled fire date of a timer. For example, a timer is setup with a fire date of 5 seconds from now, repeating every 7 seconds, and with a tolerance of 3 seconds. The timer may then fire between times 5 to 8s, 12 to 15s, 19 to 22s, 26 to 29s, and so forth.

Adding a tolerance allows the system to schedule timers in a significantly more power-friendly fashion. Most timers should have a tolerance set. A value of at least 10% of the interval is recommended, but the exact value will be application-specific.

Bug Fixes in NSFilePresenter Messaging

File coordination allows you to register an NSFilePresenter for any file or directory, even one inside a file package. For example, when you double-click on an embedded image in TextEdit to open it in Preview, Preview registers an NSFilePresenter for the image file that is inside the TextEdit .rtfd file package. In this example you might expect that when TextEdit does a coordinated write of the file package as a whole, which it does during document saving, that Preview's NSFilePresenter would be sent a -relinquishPresentedItemToWriter:. Since file coordination's introduction in Mac OS 10.7 this has not been the case. This bug has been fixed in Mac OS 10.9.

An NSFilePresenter may signal an error when invoking the completion handler passed to -savePresentedItemChangesWithCompletionHandler: or -accommodatePresentedItemDeletionWithCompletionHandler:. Since file coordination’s introduction in Mac OS 10.7, however, doing so would often cause file coordination to not invoke the reacquisition block provided by your NSFilePresenter in its response to a previous invocation of -relinquishPresentedItemToReader: or -relinquishPresentedItemToWriter: for the same coordinated reading or writing. This bug has been fixed in Mac OS 10.9. Now your NSFilePresenter’s reacquisition blocks are always invoked, even when your NSFilePresenter has signaled a failure to save changes or accommodate deletion.

Bug Fix in Key Value Observing (KVO)

Mac OS 10.8 and earlier had a bug in which KVO could send an -observeValueForKeyPath:ofObject:change:context: to an observer after it was no longer an observer, and in some cases even after the observer was deallocated. This could happen, for example, if an object had multiple observers of key paths, and the implementation of -observeValueForKeyPath:ofObject:change:context: for one observer attempted to removed one of the other observers. The removal would not take effect immediately enough to prevent the messaging of the other observer's zombie. This was possible even when just one thread was involved. This bug has been fixed in Mac OS 10.9.

Progress Reporting and Cancellation

Mac OS 10.9 includes a new mechanism for progress reporting. It allows code that does work to report the progress of that work, and user interface code to observe that progress so the progress can be presented to the user. Specifically, it can be used to show the user a progress bar and explanatory text, both updated properly as progress is made. It also allows work to be cancelled or paused by the user. This mechanism takes the form of a new class in the Foundation framework named NSProgress. Some design goals of this class were:

• Loose coupling. Code that does work can report the progress of that work regardless of what is observing it, or even whether it is being observed at all. To a lesser degree, code that observes progress and presents it to the user does not have to account for how the code that does the work is structured. Most of this goal is achieved simply by there being a single NSProgress class that can be used by a wide variety of progress reporters and observers.

• Composability. Code that does work can report progress without taking into account whether that work is actually just part of a larger operation whose total progress is what's really interesting to the user. To this end every NSProgress can have a single parent and multiple children. An NSProgress representing the total progress of an operation that's interesting to the user typically has no parent. If there are suboperations then their progress is represented by child NSProgresses. Reports of progress being made propagate to parents. Requests for cancellation propagate to children. The subdivision of progress into a tree of NSProgresses introduces some conceptual complexity to the class but it also enables the reuse of solutions to problems like how the progress of work performed by disparate pieces of code should be used to calculate one overall progress number worth presenting to the user. For example, see -[NSProgress fractionCompleted], which returns a value that takes into account both the receiver and its children.

• Reusability. NSProgress is meant to be reused by virtually all code that can link to the Foundation framework and that makes user-presentable progress. To make it as complete a solution as possible for all progress reporting problems it even includes a mechanism for publishing progress in one process and observing the progress in others, even though that introduces cross-process localization problems that it must then also solve.

• Usability. For a class to be reusable it must be usable in the first place. In many cases a substantial obstacle to using NSProgress would be arranging for code that does work to find the exact instance of NSProgress it should use to report its progress. The size of this obstacle depends on many things, like how layered your code is (would you have to pass the NSProgress as an argument through many layers of functions and methods?), how it is already being used by multiple projects (can you even add NSProgress parameters without breaking things?), how it is divided between framework and application code (does all of this code ship at the same time?), and so on. To help you surmount this obstacle there is a notion of current progress, which is the instance of NSProgress that ought to be used to report progress when there is no obvious other option. See -[NSProgress currentProgress]. You don't have to use it in situations where you can simply pass the NSProgress in another, more explicit, way, but often it will be the easiest way for progress reporters and observers to find each other. For example, you can expect that as Cocoa itself gets better at reporting progress your code will observe that progress by setting the current progress before invoking Cocoa methods that do work. (It does not matter whether the work will be done asynchronously and won't have been completed when the invoked method returns.) Likewise, as Cocoa gets better at observing progress and presenting it to the user for you your code will most likely take advantage of that by creating one or more children of the current progress and using them.

You can look at <Foundation/NSProgress.h> for detailed information about what NSProgress does, but here is some basic information about using it.

Reporting Progress

Using NSProgress in simple situations is not too complicated, though getting progress reporting and error handling right at the same time requires some care. Here's an example of doing that in a method that is supposed to be reusable regardless of whether the code that's invoking it will actually present its progress to the user, and even regardless of whether the work it's doing is just part of a larger operation:

- (BOOL)readFromData:(NSData *)data error:(NSError **)outError {
 
    // If there is already current progress, make a child of it to report progress about the part of the work
             that's being done by this method. In this example we simply use "bytes of input" as the unit of
             progress.
    NSUInteger length = [data length];
    NSProgress *progress = [NSProgress
        progressWithTotalUnitCount:length];
 
    // A loop that does something with each byte of data.
    NSError *error = nil;
    for (NSUInteger index = 0; index<length; index++) {
 
        // For the most part cancellation is just another kind of error to Cocoa. In real code there might
                       be some cleanup to do here, but it should be just more of the same thing that you would do
                       after any kind of error.
        if ([progress isCancelled]) {
            error = [NSError errorWithDomain:NSCocoaErrorDomain
                code:NSUserCancelledError userInfo:nil];
            break;
        }
 
        // Do some work with each byte. This code also might set the error to something, clean up, and
                       break out of the loop.
        […]
 
        // Report progress. Do you see why we add one to the index?
        [progress setCompletedUnitCount:(index + 1)];
 
    }
 
    // Finish up the error handling.
    if (error && outError) {
        *outError = error;
    }
    return error ? NO : YES;
 
}

Observing Progress

For the most part, observing progress means creating an NSProgress and adding key-value observers of properties like "indeterminate," "fractionCompleted," and "localizedDescription" to it. On OS X you'll often be able to do this using Cocoa Bindings. You can also use Cocoa Bindings to hook up a Cancel button so that -[NSProgress cancel] is invoked when it's pressed.

After that you have to leave the instance of NSProgress somewhere the code that will actually do work can find it. Here's an example of how you do that:

- (void)openFromFileAtURL:(NSURL *)url{
 
    // This is a method for some sort of controller object that reads model objects from a file, presenting a
             progress panel if that takes too long, and presenting an error panel if that fails.
 
    // The progress panel that might be presented has AppKit controls that are bound to properties of this
             object like "progress.localizedDescription", "progress.indeterminate",
             "progress.fractionCompleted" and, for whether the Cancel button is enabled,
             "progress.cancellable". The total unit count we use for this operation is arbitrary. What matters is
             that the counts of units we attribute to suboperations add up to it.
    _progress = [NSProgress progressWithTotalUnitCount:10];
 
    // Set properties like the localizedDescription of the NSProgress so they appear in the progress panel,
             if one is presented.
    […]
 
    // Set a timer that will present the progress panel if it goes off before the work is done. You don't want
             to present a progress panel immediately because if the work gets done instantaneously then the user
             will see a big flicker. A delay of a second is good.
    […]
 
    // You didn't really think we were going to show you how to block the main thread, did you? Our
             progress panel wouldn't even redraw or let you hit the Cancel button if we did that.
    [_concurrentQueue addOperationWithBlock:^(void) {
 
        // To take advantage of NSData's progress reporting, which will matter if the file is large
                       enough or slow enough to open, make our progress the current one before we ask NSData to
                       read the file. NSData will add a child NSProgress and report its reading progress through
                       that. After a little bit of theoretical experimentation, we theoretically determined that in this
                       example it's reasonable to call the actual reading of the file 20% of the work, and the parsing
                       of the file and the creation of objects from it the other 80%. Some files, like those on network
                       drives, take longer to read than others though. This is not an exact science.
        NSError *error = nil;
        BOOL didRead = NO;
        [_progress becomeCurrentWithPendingUnitCount:2];
        NSData *data = [NSData dataWithContentsOfURL:url options:0
            error:&error];
        [_progress resignCurrent];
        if (data) {
 
            // Once Apple adds progress reporting to NSData we're not likely to remove it, but there
                                are lots of cases where you won't know for sure whether the code you're invoking
                                actually does progress reporting. It's a good idea to record the completion of work even
                                when its progress was probably already reported with a child NSProgress, in case the
                                child NSProgress somehow didn't happen after all.
            [_progress setCompletedUnitCount:2];
 
            // -readFromData:error:, shown above in "Reporting Progress," does 80% of the work
                                here but its progress reporting is reusable in situations where it's some other fraction of
                                the work. This sort of thing is a much bigger deal when the code involved is spread all
                                over a large code base built for reusability.
            [_progress becomeCurrentWithPendingUnitCount:8];
            didRead = [self readFromData:data error:&error];
            [_progress resignCurrent];
            if (didRead) {
 
                // Done. 8 + 2 = 10.
                [_progress setCompletedUnitCount:10];
 
            }
 
        }
 
        // Get back on the main thread to do whatever it is this app does with the objects it just created.
        [[NSOperationQueue mainQueue] addOperationWithBlock:^(void) {
 
            // Success or failure, if our progress panel was presented then tear it down, and clean up.
            […]
            _progress = nil;
 
            // Success or failure?
            if (didRead) {
 
                // Do what we do.
                […]
 
            } else {
 
                // You never have to tell the user they hit the Cancel button! AppKit's error
                                          presentation methods in NSResponder and its subclasses take care of not doing
                                          that for you, but we're not using one of those here.
                BOOL errorIsCocoa = [[error domain]
                    isEqualToString:NSCocoaErrorDomain];
                if (!(errorIsCocoa &&
                    [error code]==NSUserCancelledError)) {
                    [self presentError:error];
                }
 
            }
 
        }];
 
    }];
 
}

Reporting Progress to Other Processes

There are a variety of reasons why a process might require the progress of work it's doing to be presented by another process. For just one example, in Mac OS 10.9, when Safari downloads a file the progress of that downloading is presented by Finder, on the file's icon, and by the Dock, on the containing folder's Dock item. To make that sort of thing possible instances of NSProgress can be published. See the -publish and -unpublish methods.

Observing Progress in Other Processes

A process that can present progress made by other processes must discover that progress is even being made in the first place. Continuing with the example of Finder and the Dock subscribing to find out what's happening to files, see the +addSubscriberForFileURL:withPublishingHandler: and +removeSubscriber: methods.

Localized Text in Cross-Process Progress

Not every process in a running OS X system is necessarily running with the same localization, so care must be taken that text about progress is localized in the process that will present it to the user. To make this feasible, NSProgress encapsulates the creation of progress text for presenting to the user. See the localizedDescription, localizedAdditionalDescrption, and kind properties.

NSProgresses Have User Info Dictionaries

NSProgress follows the pattern established by NSError, in which all localized text generated by the Foundation framework is derived, at least in part, from values found in a user info dictionary attached to each instance. See user info keys like NSProgressFileOperationKindKey. Entries in the user info dictionary also affect how an NSProgress is published, so see NSProgressFileURLKey for example too.

You can put entries in an NSProgress' user info dictionary for your own purposes. If the values are property list objects then they will be preserved when an NSProgress published by one process is observed by another.

NSURL

The "file" URL scheme is defined so that no authority, an empty host, and "localhost" all mean the end-user's machine. To reduce memory use, file URL objects created with file system paths or from file system representation no longer include the host string "localhost".

This change also means -host no longer returns the string "localhost" for file URLs and will instead return nil.

-initFileURLWithFileSystemRepresentation:isDirectory:relativeToURL:, +fileURLWithFileSystemRepresentation:isDirectory:relativeToURL:, -getFileSystemRepresentation:maxLength:. and -fileSystemRepresentation were added to allow easy conversion from file system representation to URL and URL to file system representation.

-removeCachedResourceValueForKey:, and -removeAllCachedResourceValues were added to allow removal of cached resource values from a URL object. -setTemporaryResourceValue:forKey: provides a way to set temporary resource values on a URL object.

URL objects created from URL strings where the URL string length was exactly 1 can no longer be created with characters not allowed in URL strings. This change affects CFURL's CFURLCreateWithString(), and the NSURL methods -initWithString:, -initWithString:relativeToURL:, +URLWithString:, and +URLWithString:relativeToURL:.

Added -stringByAddingPercentEncodingWithAllowedCharacters: and -stringByRemovingPercentEncoding. -stringByAddingPercentEncodingWithAllowedCharacters: is intended to percent-encode an URL component or subcomponent string, NOT the entire URL string. The predefined NSCharacters sets returned by +URLUserAllowedCharacterSet, +URLPasswordAllowedCharacterSet, +URLHostAllowedCharacterSet, +URLPathAllowedCharacterSet, +URLQueryAllowedCharacterSet, and +URLFragmentAllowedCharacterSet are intended to be passed to -stringByAddingPercentEncodingWithAllowedCharacters:.

The descriptions of long URLs with the data scheme may be truncated if the data URL is very large.

NSURLComponents

NSURLComponents is a new class which encapsulates the components of a URL in an object-oriented manner. When a NSURLComponents is created from a NSURL or URL string, it provides IETF STD 66 (rfc3986) parsing of the URL string. When it is used to create a NSURL by providing the components and subcomponents which make up a URL (scheme, host, port, path, query and so on), the URL is created using IETF STD 66 (rfc3986) rules. NSURLComponents makes it easy to correctly parse an existing NSURL or URL string, makes it easy to create a correctly formed NSURL from URL components and makes it easy to create a new NSURL from an existing URL with modifications.

Custom NSData Deallocator for No-Copy Buffers

NSData has long provided the ability to create instances that use a buffer provided by you, instead of copying its contents to an internally created buffer. The APIs to do this are -[NSData initWithBytesNoCopy:length:] and -[NSData initWithBytesNoCopy:length:freeWhenDone:]. One limitation of these APIs is that if you wish to defer deallocation of the no-copy buffer to the NSData instance, then you must use malloc(3) (or one if its variants), because NSData will use free(3).

To eliminate this limitation, NSData has added an API In OS X 10.9 that allows you to specify a custom method of deallocation via a block parameter. That API is -[NSData initWithBytesNoCopy:length:deallocator:].

There are some important things to be aware of when using this API. NSData will, when necessary, copy the deallocator block onto the heap. As a byproduct, any Objective-C object pointers that are captured in that block will be retained. In order to avoid any inadvertent retain cycles, you should avoid capturing pointers to any objects that may in turn retain the NSData object, including explicit references to self and implicit ones via instance variable referencing. To assist in this, the deallocator block has two parameters, the buffer's pointer its length. You should always use these values instead of trying to use references from outside the block.

NSData API for Base 64 Encoding and Decoding

NSData has added an API in OS X 10.9 for encoding and decoding Base 64. The encoding algorithm can be configured to automatically insert line breaks with customizable line ending characters. The decoding algorithm by default will reject the entire input if it encounters any non-Base 64 characters (including whitespace), but there is an option available to make it more lenient. Depending on your needs, you can use one of the two variants of the encoding and decoding methods. One pair uses Base 64 encoded NSStrings and the other uses Base 64 encoded NSDatas.

If your application needs to target an operating system prior to OS X 10.9, you can use NSData's -initWithBase64Encoding: and -base64Encoding instead. These methods have existed since OS X 10.6, but were not exposed until OS X 10.9. These methods behave like the new methods, except -initWithBase64Encoding: will ignore unknown characters. When your application no longer needs to target an operation system prior to OS X 10.9, you should transition to the new methods.

NSPurgeableData Thread Safety

Prior to OS X 10.9, NSPurgeableData was not fully thread-safe. If multiple threads were to invoke certain NSPurgeableData methods simultaneously, an exception or a crash could result. This has been resolved on OS X 10.9.

NSString -stringByAppendingPathExtension: Behavior Change

Prior to OS X 10.9, if the receiver of NSString's -stringByAppendingPathExtension: method started with a tilde (~) character, the method would silently fail to append the extension and return the string unmodified. This behavior has been changed for applications linked against the 10.9 SDK to allow this method to behave as expected for home-relative paths (e.g. "~/user/path/to/file") and terminal file names (e.g. "~tempfile").

NSFileProtectionKey Bug Fixed

Prior to iOS 7.0, when the device was locked, -[NSFileManager attributesOfItemAtPath:error:] would return a dictionary without NSFileProtectionKey. This has been fixed on iOS 7.0 so that the returned dictionary will report the proper NSFileProtectionKey value.

NSFileManager Delegate Method Bug Fixed

Prior to OS X 10.9, delegate implementations of the NSFileManagerDelegate method -fileManager:shouldProceedAfterError:removingItemAtURL: would never be invoked. This has been fixed on OS X 10.9. To work around the problem, you can use the -fileManager:shouldProceedAfterError:removingItemAtPath: method instead. If implemented, that method will be invoked regardless of whether you invoked -removeItemAtPath:error: or -removeItemAtURL:error:.

NSData +dataWithData: Behavior Change

Prior to OS X 10.9, it was possible for -[NSData dataWithData:] to return a new NSData instance, even when the receiver was immutable. In OS X 10.9, this method may start returning the same pointer as the receiver (with its retain count incremented) to avoid unnecessary memory allocation. This is possible because NSData's immutability applies to both its 'bytes' pointer and the contents of the pointed-to buffer.

In rare scenarios, the change described above may cause unexpected behavior for NSData objects created with one of the "NoCopy" initializers. Since a new NSData instance is not created and the buffer is not copied, changes to the buffer of one NSData may unexpectedly affect another's. To avoid this, you should ensure that you never modify a buffer after passing it to one of NSData's "NoCopy" initializers, even if NSData is not responsible for deallocating that buffer.

If you need to create an NSData that contains a copy of an existing NSData's buffer, you can do something like [NSData dataWithBytes:[otherData bytes] length:[otherData length]].

NSUserDefaults support for Security Application Groups (Sandboxing)

For applications that are part of a Security Application Group, the NSUserDefaults "suite" APIs (-initWithSuiteName:, -addSuiteNamed: and -removeSuiteNamed:) will operate on a suite shared by applications in the group and stored in the group container, if the suite identifier is the identifier of the group.

Changes to NSUserDefaults "compatibility" keys

The deprecated constant user defaults keys at the bottom of NSUserDefaults.h are no longer functional in applications built with the 10.9 or later SDK.

Improved safety of NSUserDefaults values

Validation that values set in NSUserDefaults are valid Property List types has been made more thorough, and easier to debug. Crash logs from failing to do this will now include additional information noting the problem.

Collections returned from NSUserDefaults have always been documented to be immutable, but for applications built with the 10.9 or later SDK, actually are now. Attempting to mutate these collections on earlier releases led to extremely hard to diagnose bugs.

Nonsensical parameters to "Suite" methods on NSUserDefaults will now be rejected with a logged message. Currently the cases rejected are NSGlobalDomain and the bundle identifier of the main bundle.

-[NSUserDefaults synchronize] and non-current-application domains

In earlier releases, -[NSUserDefaults synchronize] synchronized only the current application's search list. In 10.9 and later it also synchronizes any other domains with un-synchronized changes.

-[NSUserDefaults synchronize] is not generally useful

You should only need to call -synchronize if a separate application will be reading the default that you just set, or if a process that does not use AppKit is terminating. In most applications neither of these should ever occur, and -synchronize should not be called. Note that prior to Mac OS X 10.8.4 there was a bug that caused AppKit to automatically synchronize slightly prematurely during application termination, so preferences set in response to windows closing while the application is terminating might not be saved; this has been fixed.

dispatch_data_t -> NSData bridging

In 64-bit apps using either manual retain/release or ARC, dispatch_data_t can now be freely cast to NSData *, though not vice versa. Note that one implication of this is that NSData objects created by Cocoa may now contain several discontiguous pieces of data. You can efficiently work with discontiguous ranges of data by using the new

- (void) enumerateByteRangesUsingBlock:(void (^)(const void *bytes, NSRange byteRange, BOOL *stop))block

API on NSData. This will be roughly the same speed as -bytes on a contiguous NSData, but avoid allocation and copying for a discontiguous one. Once a discontiguous NSData is compacted to a contiguous one (generally by calling -bytes, other NSData API will do discontiguous accesses), future accesses to the contiguous region will not require additional copying.

Various system APIs (in particular NSFileHandle) have been updated to use discontiguous data for improved performance, so it's best to structure your code to handle it unless it absolutely needs contiguous bytes.

Empty NSData objects

Immutable NSData objects with a length of zero are now all a single object. This shouldn't matter for most applications, but relying on the == operator or methods like -indexOfObjectIdenticalTo: to distinguish between empty data objects will no longer work.

Immutable NSData objects may be vm-backed

Starting in 10.9, NSData may choose to allocate its backing store with vm_allocate, rather than malloc. This should not impact behavior at all, but may be useful to know when examining your program with memory analysis tools (vmmap, Instruments, etc…). This also means that transferring NSData objects over NSXPCConnection can remap the pages rather than copying them, which can improve performance.

NSData -copy, -copyWithZone: and -initWithData:

Methods that create copies of NSData have been improved to simply retain if it's safe to do so in more cases. This shouldn't matter for most applications, but relying on the == operator or methods like -indexOfObjectIdenticalTo: to distinguish between copied data objects will be less likely to work than in the past.

plutil(1) plist editing

plutil(1) has four additional verbs: insert, replace, extract, and remove, which can be used to manipulate plist files. Run 'plutil -help' for more information.

defaults(1) additions for dealing with arbitrary plist files

defaults(1) has two additional verbs: import and export. These can be used to add the contents of a property list file to a defaults domain, or save the contents of a defaults domain as a property list file.

NSCalendar performance and thread-safety

Prior to 10.9, NSCalendar was not thread-safe, which required the +currentCalendar and -copy/-copyWithZone: methods to make time consuming full copies. This has been improved so that expensive copy operations will be deferred until the object is mutated. If you can avoid calling setter methods on NSCalendar instances, you'll likely get better performance.

NSTask performance and thread-safety

NSTask is now thread-safe, and significantly more efficient, especially when launching tasks from host processes with very large VSIZEs and/or unusual memory mappings.

NSDateFormatter and NSNumberFormatter thread-safety

When set to the modern formatter behavior (NSNumberFormatterBehavior10_4), NSNumberFormatter instances are now thread-safe. When set to the modern formatter behavior and using the non-fragile ABI (64 bit applications, on OSX), NSDateFormatter instances are also thread-safe.

NSNetServices

A new includesPeerToPeer property was added to NSNetService and NSNetServiceBrowser to enable Bonjour discovery and connectivity over peer-to-peer Wi-Fi and Bluetooth.

A new NSNetServiceListenForConnections option was added to -publishWithOptions: that allows a published NSNetService to listen for incoming TCP connections. New connections are delivered in the form of NSStreams via the new -netService:didAcceptConnectionWithInputStream:outputStream: delegate method.

NSURLSession

NSURLSession is a replacement API for NSURLConnection. It supports out-of-process downloads and uploads that notify your app on completion.  In addition, it provides a new way to configure your networking requests (NSURLRequest) so that they don't conflict with other networking code in your application.

NSURLCredential

Use the new NSURLCredentialPersistenceSynchronizable persistence policy flag to sync the credential across devices through iCloud.

The new -[NSURLCredentialStorage removeCredential:forProtectionSpace:options:] API can be used to remove a credential that has a persistence policy of NSURLCredentialPersistenceSynchronizable.  If the passed in NSURLCredential object has a persistence policy of NSURLCredentialPersistenceSynchronizable, and if the options dictionary is present and includes the NSURLCredentialStorageRemoveSynchronizableCredentials key set to YES, the remove will attempt to delete the credential from iCloud, which will result in the credential being removed from all synchronized devices.  If the passed in NSURLCredential object has a persistence policy of NSURLCredentialPersistenceSynchronizable and no options dictionary is provided, or NSURLCredentialStorageRemoveSynchronizableCredentials does exist but is set to NO, then the call will fail.  Passing in an NSURLCredential with a persistence policy other than NSURLCredentialPersistenceSynchronizable is the same as calling the existing -[NSURLCredentialStorage removeCredential:forProtectionSpace:] method.

NSPredicate, NSExpression, and NSSortDescriptor

NSPredicate, NSExpression, and NSSortDescriptor now support NSSecureCoding.

While it is safe to unarchive these objects using NSSecureCoding, it is not safe to blindly evaluate anything you get out of the archive, and as such, evaluation of securely decoded objects will be disabled. Any process receiving predicates/expressions/sortDescriptors should preflight the content of the archive by validating keypaths, selectors, etc contained within it to ensure no erroneous or malicious code will be executed. Once preflighting has been done, evaluation can be enabled by invoking allowEvaluation on the decoded object to recursively enable evaluation on the object graph rooted at the receiver.

NSCalendar

In OS X 10.9, Foundation provides many new APIs to simplify calendrical calculations. This also helps to avoid mistakes from complex calendrical calculations. The new APIs are:

+ (id)calendarWithIdentifier:(NSString *)calendarIdentiferConstant;
- (void)getEra:(out NSInteger *)eraValuePointer year:(out NSInteger *)yearValuePointer
           month:(out NSInteger *)monthValuePointer day:(out NSInteger *)dayValuePointer fromDate:(NSDate *)date;
- (void)getEra:(out NSInteger *)eraValuePointer yearForWeekOfYear:(out NSInteger *)yearValuePointer
           weekOfYear:(out NSInteger *)weekValuePointer weekday:(out NSInteger *)weekdayValuePointer fromDate:(NSDate *)date;
- (void)getHour:(out NSInteger *)hourValuePointer minute:(out NSInteger *)minuteValuePointer second:(out NSInteger *)secondValuePointer
           nanosecond:(out NSInteger *)nanosecondValuePointer fromDate:(NSDate *)date;
- (NSInteger)component:(NSCalendarUnit)unit fromDate:(NSDate *)date;
- (NSDate *)dateWithEra:(NSInteger)eraValue year:(NSInteger)yearValue month:(NSInteger)monthValue day:(NSInteger)dayValue
           hour:(NSInteger)hourValue minute:(NSInteger)minuteValue second:(NSInteger)secondValue nanosecond:(NSInteger)nanosecondValue;
- (NSDate *)dateWithEra:(NSInteger)eraValue yearForWeekOfYear:(NSInteger)yearValue weekOfYear:(NSInteger)weekValue
           weekday:(NSInteger)weekdayValue hour:(NSInteger)hourValue minute:(NSInteger)minuteValue second:(NSInteger)secondValue nanosecond:(NSInteger)nanosecondValue;
- (NSDate *)startOfDayForDate:(NSDate *)date;
- (NSDateComponents *)componentsInTimeZone:(NSTimeZone *)timezone fromDate:(NSDate *)date;
- (NSComparisonResult)compareDate:(NSDate *)date1 toDate:(NSDate *)date2 toUnitGranularity:(NSCalendarUnit)unit;
- (BOOL)isDate:(NSDate *)date1 equalToDate:(NSDate *)date2 toUnitGranularity:(NSCalendarUnit)unit;
- (BOOL)isDate:(NSDate *)date1 inSameDayAsDate:(NSDate *)date2;
- (BOOL)isDateInToday:(NSDate *)date;
- (BOOL)isDateInYesterday:(NSDate *)date;
- (BOOL)isDateInTomorrow:(NSDate *)date;
- (BOOL)isDateInWeekend:(NSDate *)date;
- (BOOL)rangeOfWeekendStartDate:(out NSDate **)datep interval:(out NSTimeInterval *)tip containingDate:(NSDate *)date;
- (BOOL)nextWeekendStartDate:(out NSDate **)datep interval:(out NSTimeInterval *)tip options:(NSCalendarOptions)options afterDate:(NSDate *)date;
- (NSDateComponents *)components:(NSCalendarUnit)unitFlags fromDateComponents:(NSDateComponents *)startingDateComp
           toDateComponents:(NSDateComponents *)resultDateComp options:(NSCalendarOptions)options;
- (NSDate *)dateByAddingUnit:(NSCalendarUnit)unit value:(NSInteger)value toDate:(NSDate *)date options:(NSCalendarOptions)options;
- (void)enumerateDatesStartingAfterDate:(NSDate *)start matchingComponents:(NSDateComponents *)comps options:(NSCalendarOptions)opts
           usingBlock:(void (^)(NSDate *date, BOOL exactMatch, BOOL *stop))block;
- (NSDate *)nextDateAfterDate:(NSDate *)date matchingComponents:(NSDateComponents *)comps options:(NSCalendarOptions)options;
- (NSDate *)nextDateAfterDate:(NSDate *)date matchingUnit:(NSCalendarUnit)unit value:(NSInteger)value options:(NSCalendarOptions)options;
- (NSDate *)nextDateAfterDate:(NSDate *)date matchingHour:(NSInteger)hourValue minute:(NSInteger)minuteValue second:(NSInteger)secondValue options:(NSCalendarOptions)options;
- (NSDate *)dateBySettingUnit:(NSCalendarUnit)unit value:(NSInteger)v toDate:(NSDate *)date options:(NSCalendarOptions)opts;
- (NSDate *)dateBySettingHour:(NSInteger)h minute:(NSInteger)m second:(NSInteger)s toDate:(NSDate *)date options:(NSCalendarOptions)opts;

More details about these new APIs can be found in NSCalendar.h. The Date and Time Programming Guide also has more detail discussion about how these APIs would be used.

In addition to the new APIs, Foundation also exports a new notification: NSCalendarDayChangeNotification. This new notification is posted through [NSNotificationCenter defaultCenter] when the system day changes. Note that the notification is not posted to observers on any particular or defined thread or queue, so if you need the handling of the notification to do things that must only be done by a specific thread or queue, you need to then schedule that work in response to the notification.

CoreFoundation and Foundation are going to deprecate several existing calendar-related APIs in the next release. If the preprocessor macro NS_ENABLE_CALENDAR_DEPRECATIONS is set to a non-zero value in a project, then usage of those APIs will be indicated by the compiler.

NSDateComponents

NSDateComponents has four new APIs for convenience:

- (void)setValue:(NSInteger)value forComponent:(NSCalendarUnit)unit;
- (NSInteger)valueForComponent:(NSCalendarUnit)unit;
- (BOOL)isValidDate;
- (BOOL)isValidDateInCalendar:(NSCalendar *)calendar;

More details about these new APIs can be found in NSCalendar.h.

instancetype Adoption

Many new core APIs of Foundation use the 'instancetype' return type. These are class methods which return an instance of the receiving class, even if the receiving class is a subclass of the class which declares the method. Typically these methods would have returned 'id' in the past.

This information can help the compiler identify basic kinds of errors, like the NSArray type in the following line:

    NSArray *set = [NSSet setWithObject:@"A String"];

But conversely, note that just because a method is a class method and returns an instance of the class, it does not necessarily follow that it will return an instance of an arbitrary subclass if the method is sent to the subclass. Thus, not all class methods which return instances are necessarily true candidates for the 'instancetype' return value.

NSArray -firstObject

The -firstObject method returns the first object in the array, or nil if the array is empty.

NSString Errors

NSString out-of-bounds index and ranges now generate better error messages.

Formatting localized numbers with NSStrings using the "+" flag will now will no longer display an extra "+" for negative numbers. However, the "+" is not localized.

NSScanner

NSScanner now provides the following API to scan unsigned long long values:

- (BOOL)scanUnsignedLongLong:(unsigned long long *)value;

This works exactly like other existing NSScanner methods, including the caveats:

- it doesn't scan localized numbers or numbers with thousands separators

- returns YES on overflow, with a clamped result

NSAttributedString

For applications linked against the 10.9 SDK or later, copying a standard instance of NSAttributedString now retains it instead.

Localized Property List File

Many languages including English have grammatical rules for selecting a word form depending on contextual conditions such as the gender or plurality.  For example, it is common to manually implement the logic for selecting singular or plural forms in formatting localized strings.

NSString *localizedString;
NSUInteger numberOfItems; // assume the number of selected item is stored
 
if (numberOfItems == 1) { // single item
    localizedString = NSLocalizedString(@"A file is selected", @"Message displayed when showing a single file selection.");
} else { // multiple item
    localizedString = [NSString localizedStringWithFormat:NSLocalizedString(@"%d files are selected", @"Message displayed when showing multiple file selection."), numberOfItems];
}

The rule gets more complex when dealing with languages requiring the gender-based form selection and/or plural form condition. For languages such as Russian and Arabic with multiple plural forms, properly formatting by conditional logic like above becomes extremely hard to maintain.

To show the complexity, the following code snippet illustrates what would happen to support the Arabic plural logic for the same message selection logic shown above.

NSString *localizedString;
NSUInteger numberOfItems; // assume the number of selected item is stored
NSUInteger modValue = numberOfItems % 100;
 
if (numberOfItems == 0) { // no item
    localizedString = NSLocalizedString(@"No file is selected", @"Message displayed when showing no selection.");
} else if (numberOfItems == 1) { // single item
    localizedString = NSLocalizedString(@"A file is selected", @"Message displayed when showing a single file selection.");
} else if (numberOfItems == 2) { // dual items
    localizedString = NSLocalizedString(@"Two files are selected", @"Message displayed when showing two files selected.");
} else if ((modValue >= 3) && (modValue <= 10)) { // paucal items
    localizedString = [NSString localizedStringWithFormat:NSLocalizedString(@"A few files (%d items) are selected", @"Message displayed when showing paucal files selected."), numberOfItems];
} else { // multiple items
    localizedString = [NSString localizedStringWithFormat:NSLocalizedString(@"%d files are selected", @"Message displayed when showing multiple file selection."), numberOfItems];
}

Further complicating the issue, the logic for choosing from multiple plural forms varies from locale to locale.

In order to solve this issue, the localizers need to be able to specify more sophisticated data structure than the simple key-value pair from the strings file format. There is a new file format with ".stringsdict" suffix introduced. -[NSBundle localizedStringForKey:value:table:] now accesses two files: .stringsdict and .strings.  It queries the .stringsdict file first, then, .strings file.

The .stringsdict file contains the original key (i.e. @"%d files are selected") with the value as an arbitrary property list (mostly dictionary or string). When the value is a dictionary, it must contain a key for the localized format string value and its format specifier configuration dictionaries.

When -localizedStringForKey:value:table: returns an NSString instantiated from an entry in a .stringsdict file, the string object carries the additional information stored in the file.  The information can be retained and copied across -copy and -mutableCopy.  It gets discarded when a mutable copy gets mutated.

NSString %@ format specifier enhancement

For representing a new dictionary based formatting rule, %@ format directive is enhanced with the alternate form flag '#'.

The extended %@ format syntax is:

%[n$]#[FLAGS][FIELD WIDTH][.PRECISION]@<CONFIGURATION KEY>@

A configuration key between two @s is used to query an item in the external format configuration dictionary.  Only characters in [a-zA-Z_0-9] are allowed.  The name space is independent for each format string.

For example, @"%d files are selected" can become @"%#@num_files_are@ selected" referencing an item for "num_files_are" in the external format configuration dictionary.

The format specifier configuration dictionary

The format specifier configuration dictionary contains key-value pairs of configuration data.  Each value is represented by itself a dictionary.

There are a couple of dictionary keys predefined.

- NSStringFormatSpecTypeKey

This key defines the type of format specifier configuration.  This is a mandatory key.  Currently we're supporting NSStringPluralRuleType and NSStringGenderRuleType.  The rest of dictionary contents is determined by the type.

- NSStringFormatValueTypeKey

This is an optional key describing the original argument type on the stack.  The value is the original format specifier.  For mapping @"%d files are selected" to @"%#@num_files_are@ selected", the configuration dictionary for num_files_are should contain an entry "NSStringFormatValueTypeKey = d".  If absent, %@ is assumed.

The NSStringPluralRuleType configuration maps the argument number into a plural choice using the Unicode CLDR Plural mapping rule.  The configuration dictionary could contain keys for "zero", "one", "two", "few", "many", and "others".  They correspond to the Unicode CLDR Plural supplement data items.  The value for "others" is mandatory.  If "zero" is present, the value is used for mapping the argument value zero regardless of what CLDR rule specifies for the numeric value.  If a mapping key is absent, the value for "others" is used as the fallback.

The NSStringGenderRuleType configuration maps the argument number to a variant form.  As with most other gender variation handling systems including CLDR, we're assigning index numbers to genders.  For example, male is 0, female is 1, and neutral is 2.  Since the number of gender types varies greatly from languages to languages (i.e. Polish has 5).  The key for this configuration info type is represented by a positive integer number.  The key 0 is mandatory and used for absence of other gender keys.

The mapped value itself can be a format string.  The format string is evaluated with the value used to select it.

Sample configuration information for the selected file example.

@"%d files are selected" = @"%#@num_files_are@ selected" // localized string dynamically substitute "%d files are"

The configuration dict is:

{
    "NSStringFormatSpecTypeKey" = "NSStringPluralRuleType"; // plural type
    "NSStringFormatValueTypeKey" = "d"; // int argument
 
    "zero" = "No file is";
    "one" = "A file is";
    "other" = "%d files are";
}

Since there are cases where the condition of a plural/gender rule substitution is depending on another substitution (i.e. French articles like le, la, and les), the recursive formatting capability is essential for this feature.  For example, with @"%d in %d files are selected", giving localizers options to substitute the whole sentence depending on the number of total files is necessary.  We're allowing the recursive formatting by applying the entire argument list to each substituted format specifier.

@"%d in %d files are selected" = @"%2$#@d_in_d_files_are_selected@"

The configuration dictionary can contain

"d_in_d_files_are_selected" = {
    "NSStringFormatSpecTypeKey" = "NSStringPluralRuleType"; // plural type
    "NSStringFormatValueTypeKey" = "d"; // int argument
 
    "zero" = "There is no file";
    "one" = "There is a file, and %1$#@it_is_selected@";
    "other" = "%1$d in %2$d files are selected";
};
 
"it_is_selected" = {
    "NSStringFormatSpecTypeKey" = "NSStringPluralRuleType"; // plural type
    "NSStringFormatValueTypeKey" = "d"; // int argument
 
    "zero" = "it is not selected";
    "other" = "it is selected";
};

The results are "There is no file" for 0 files, "there is a file, and it is not selected" for 0 in 1, and "3 in 5 files are selected" for 3 in 5.

This is a sample stringsdict contents:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>%d files are selected</key>
    <dict>
        <key>NSStringLocalizedFormatKey</key>
        <string>%#@num_files_are@ selected</string>
        <key>num_files_are</key>
        <dict>
            <key>NSStringFormatSpecTypeKey</key>
            <string>NSStringPluralRuleType</string>
            <key>NSStringFormatValueTypeKey</key>
            <string>d</string>
            <key>zero</key>
            <string>No file is</string>
            <key>one</key>
            <string>A file is</string>
            <key>other</key>
            <string>%d files are</string>
        </dict>
    </dict>
</dict>
</plist>