UIKit Function Reference

Framework	UIKit/UIKit.h
Declared in	NSText.h UIAccessibility.h UIAccessibilityZoom.h UIApplication.h UIDevice.h UIGeometry.h UIGraphics.h UIImage.h UIImagePickerController.h

Overview

The UIKit framework defines a number of functions, many of them used in graphics and drawing operations.

Functions by Task

Application Launch

Image Manipulation

Image and Movie Saving

Graphics

PDF Creation

String Conversions

Managing Edge Insets

Managing Offsets

Interface Orientation Macros

Device Orientation Macros

Interface Idiom Macro

Accessibility

Text Manipulations

Functions

CGAffineTransformFromString

Returns a Core Graphics affine transform structure corresponding to the data in a given string.

CGAffineTransform CGAffineTransformFromString (
   NSString *string
);

Parameters

string: A string whose contents are of the form “{a, b, c, d, tx, ty}”, where a, b, c, d, tx, and ty are the floating-point component values of the CGAffineTransform data structure. An example of a valid string is @”{1,0,0,1,2.5,3.0}”. The string is not localized, so items are always separated with a comma. For information about the position of each value in the transform array, see CGAffineTransform Reference.

Return Value

A Core Graphics affine transform structure. If the string is not well-formed, the function returns the identity transform.

Discussion

In general, you should use this function only to convert strings that were previously created using the NSStringFromCGAffineTransform function.

Availability

Available in iOS 2.0 and later.

Declared In

UIGeometry.h

CGPointFromString

Returns a Core Graphics point structure corresponding to the data in a given string.

CGPoint CGPointFromString (
   NSString *string
);

Parameters

string: A string whose contents are of the form “{x,y}”, where x is the x coordinate and y is the y coordinate. The x and y values can represent integer or float values. An example of a valid string is @”{3.0,2.5}”. The string is not localized, so items are always separated with a comma.

Return Value

A Core Graphics structure that represents a point. If the string is not well-formed, the function returns CGPointZero.

Discussion

In general, you should use this function only to convert strings that were previously created using the NSStringFromCGPoint function.

Availability

Available in iOS 2.0 and later.

Declared In

UIGeometry.h

CGRectFromString

Returns a Core Graphics rectangle structure corresponding to the data in a given string.

CGRect CGRectFromString (
   NSString *string
);

Parameters

string: A string whose contents are of the form “{{x,y},{w, h}}”, where x is the x coordinate, y is the y coordinate, w is the width, and h is the height. These components can represent integer or float values. An example of a valid string is @”{{3,2},{4,5}}”. The string is not localized, so items are always separated with a comma.

Return Value

A Core Graphics structure that represents a rectangle. If the string is not well-formed, the function returns CGRectZero.

Discussion

In general, you should use this function only to convert strings that were previously created using the NSStringFromCGRect function.

Availability

Available in iOS 2.0 and later.

Declared In

UIGeometry.h

CGSizeFromString

Returns a Core Graphics size structure corresponding to the data in a given string.

CGSize CGSizeFromString (
   NSString *string
);

Parameters

string: A string whose contents are of the form “{w, h}”, where w is the width and h is the height. The w and h values can be integer or float values. An example of a valid string is @”{3.0,2.5}”. The string is not localized, so items are always separated with a comma.

Return Value

A Core Graphics structure that represents a size. If the string is not well-formed, the function returns CGSizeZero.

Discussion

In general, you should use this function only to convert strings that were previously created using the NSStringFromCGSize function.

Availability

Available in iOS 2.0 and later.

Declared In

UIGeometry.h

NSStringFromCGAffineTransform

Returns a string formatted to contain the data from an affine transform.

NSString * NSStringFromCGAffineTransform (
   CGAffineTransform transform
);

Parameters

transform: A Core Graphics affine transform structure.

Return Value

A string that corresponds to transform. See CGAffineTransformFromString for a discussion of the string format.

Availability

Available in iOS 2.0 and later.

Declared In

UIGeometry.h

NSStringFromCGPoint

Returns a string formatted to contain the data from a point.

NSString * NSStringFromCGPoint (
   CGPoint point
);

Parameters

point: A Core Graphics structure representing a point.

Return Value

A string that corresponds to point. See CGPointFromString for a discussion of the string format.

Availability

Available in iOS 2.0 and later.

Declared In

UIGeometry.h

NSStringFromCGRect

Returns a string formatted to contain the data from a rectangle.

NSString * NSStringFromCGRect (
   CGRect rect
);

Parameters

rect: A Core Graphics structure representing a rectangle.

Return Value

A string that corresponds to rect. See CGRectFromString for a discussion of the string format.

Availability

Available in iOS 2.0 and later.

Related Sample Code

AdvancedURLConnections

Declared In

UIGeometry.h

NSStringFromCGSize

Returns a string formatted to contain the data from a size data structure.

NSString * NSStringFromCGSize (
   CGSize size
);

Parameters

size: A Core Graphics structure representing a size.

Return Value

A string that corresponds to size. See CGSizeFromString for a discussion of the string format.

Availability

Available in iOS 2.0 and later.

Declared In

UIGeometry.h

NSStringFromUIEdgeInsets

Returns a string formatted to contain the data from an edge insets structure.

NSString * NSStringFromUIEdgeInsets (
   UIEdgeInsets insets
);

Parameters

insets: A UIKit edge insets data structure.

Return Value

A string that corresponds to insets. See UIEdgeInsetsFromString for a discussion of the string format.

Availability

Available in iOS 2.0 and later.

Declared In

UIGeometry.h

NSStringFromUIOffset

Returns a string formatted to contain the data from an offset structure.

NSString *NSStringFromUIOffset(
   UIOffset offset
);

Parameters

offset: A UIKit offset data structure.

Return Value

A string that corresponds to offset.

Availability

Available in iOS 5.0 and later.

Declared In

UIGeometry.h

NSTextAlignmentFromCTTextAlignment

Converts a Core Text alignment constant value to the matching constant value used by UIKit.

NSTextAlignment NSTextAlignmentFromCTTextAlignment(CTTextAlignment ctTextAlignment);

Parameters

ctTextAlignment: The Core text alignment constant you want to convert.

Return Value

The UIKit text alignment that corresponds to the value specified in ctTextAlignment.

Discussion

Use this function when you need to map between the Core Text and UIKit constants for text alignment.

Availability

Available in iOS 6.0 and later.

Declared In

NSText.h

NSTextAlignmentToCTTextAlignment

Converts a UIKit text alignment constant value to the matching constant value used by Core Text.

CTTextAlignment NSTextAlignmentToCTTextAlignment(NSTextAlignment nsTextAlignment);

Parameters

nsTextAlignment: The UIKit text alignment constant you want to convert.

Return Value

The Core Text alignment that corresponds to the value specified in nsTextAlignment.

Discussion

Use this function when you need to map between the UIKit and Core Text constants for text alignment.

Availability

Available in iOS 6.0 and later.

Declared In

NSText.h

UIAccessibilityIsClosedCaptioningEnabled

Returns a Boolean value indicating whether closed captioning is enabled.

BOOL UIAccessibilityIsClosedCaptioningEnabled();

Return Value

YES if the user has enabled closed captioning in Settings; otherwise, NO.

Availability

Available in iOS 5.0 and later.

Declared In

UIAccessibility.h

UIAccessibilityIsGuidedAccessEnabled

Returns a Boolean value indicating whether Guided Access is enabled.

BOOL UIAccessibilityIsGuidedAccessEnabled();

Return Value

YES if the user has enabled Guided Access in Settings; otherwise, NO.

Availability

Available in iOS 6.0 and later.

Declared In

UIAccessibility.h

UIAccessibilityIsInvertColorsEnabled

Returns a Boolean value indicating whether inverted colors is enabled.

BOOL UIAccessibilityIsInvertColorsEnabled();

Return Value

YES if the user has enabled inverted colors in Settings; otherwise, NO.

Availability

Available in iOS 6.0 and later.

Declared In

UIAccessibility.h

UIAccessibilityIsMonoAudioEnabled

Returns a Boolean value indicating whether system audio is set to mono.

BOOL UIAccessibilityIsMonoAudioEnabled();

Return Value

YES if mono audio is currently enabled; otherwise, NO.

Availability

Available in iOS 5.0 and later.

Declared In

UIAccessibility.h

UIAccessibilityIsVoiceOverRunning

Returns a Boolean value indicating whether VoiceOver is running.

BOOL UIAccessibilityIsVoiceOverRunning();

Return Value

YES if VoiceOver is currently running; otherwise, NO.

Discussion

You can use this function to customize your application’s UI specifically for VoiceOver users. For example, you might want UI elements that usually disappear quickly to persist onscreen for VoiceOver users. Note that you can also listen for the UIAccessibilityVoiceOverStatusChanged notification to find out when VoiceOver starts and stops.

Availability

Available in iOS 4.0 and later.

Declared In

UIAccessibility.h

UIAccessibilityPostNotification

Posts a notification to assistive applications.

void UIAccessibilityPostNotification (
   UIAccessibilityNotifications notification,
   id argument
);

Parameters

notification: The notification to post (see “Notifications” in UIAccessibility Protocol Reference for a list of notifications).
argument: The argument specified by the notification. Pass nil unless a notification specifies otherwise.

Discussion

Your application might need to post accessibility notifications if you have user interface components that change very frequently or that appear and disappear.

Availability

Available in iOS 3.0 and later.

Related Sample Code

Declared In

UIAccessibility.h

UIAccessibilityRegisterGestureConflictWithZoom

Warns users that application-specific gestures conflict with the system-defined Zoom accessibility gestures.

void UIAccessibilityRegisterGestureConflictWithZoom();

Discussion

Use this function if your application uses multi-finger gestures that conflict with the gestures used by system Zoom (that is, three-finger gestures). When this is the case, the user is presented with the choice of turning off Zoom or continuing.

Availability

Available in iOS 5.0 and later.

Declared In

UIAccessibilityZoom.h

UIAccessibilityZoomFocusChanged

Notifies the system that the app’s focus has changed to a new location.

void UIAccessibilityZoomFocusChanged(
   UIAccessibilityZoomType type,
   CGRect frame,
   UIView *view
);

Parameters

type: A UIAccessibilityZoomType constant that identifies the type of Zoom.
frame: The frame that is currently zoomed, in screen coordinates.
view: The view that contains the zoomed frame.

Availability

Available in iOS 5.0 and later.

Declared In

UIAccessibilityZoom.h

UIApplicationMain

This function is called in the main entry point to create the application object and the application delegate and set up the event cycle.

int UIApplicationMain (
   int argc,
   char *argv[],
   NSString *principalClassName,
   NSString *delegateClassName
);

Parameters

argc: The count of arguments in argv; this usually is the corresponding parameter to main.
argv: A variable list of arguments; this usually is the corresponding parameter to main.
principalClassName: The name of the UIApplication class or subclass. If you specify nil, UIApplication is assumed.
delegateClassName: The name of the class from which the application delegate is instantiated. If principalClassName designates a subclass of UIApplication, you may designate the subclass as the delegate; the subclass instance receives the application-delegate messages. Specify nil if you load the delegate object from your application’s main nib file.

Return Value

Even though an integer return type is specified, this function never returns. When users exits an iOS application by pressing the Home button, the application moves to the background.

Discussion

This function instantiates the application object from the principal class and instantiates the delegate (if any) from the given class and sets the delegate for the application. It also sets up the main event loop, including the application’s run loop, and begins processing events. If the application’s Info.plist file specifies a main nib file to be loaded, by including the NSMainNibFile key and a valid nib file name for the value, this function loads that nib file.

Despite the declared return type, this function never returns. For more information on how this function behaves, see ““Core App Objects”” in iOS App Programming Guide.

Availability

Available in iOS 2.0 and later.

Related Sample Code

Declared In

UIApplication.h

UIDeviceOrientationIsLandscape

Returns a Boolean value indicating whether the device is in a landscape orientation.

#define UIDeviceOrientationIsLandscape(orientation) \
   ((orientation) == UIDeviceOrientationLandscapeLeft || \
   (orientation) == UIDeviceOrientationLandscapeRight)

Parameters

orientation: Specify the value of the orientation property of the UIDevice class.

Return Value

Returns YES if the device orientation is landscape, otherwise returns NO.

Availability

Available in iOS 2.0 and later.

Related Sample Code

Declared In

UIDevice.h

UIDeviceOrientationIsPortrait

Returns a Boolean value indicating whether the device is in a portrait orientation.

#define UIDeviceOrientationIsPortrait(orientation)  \
   ((orientation) == UIDeviceOrientationPortrait || \
   (orientation) == UIDeviceOrientationPortraitUpsideDown)

Parameters

orientation: Specify the value of the orientation property of the UIDevice class.

Return Value

Returns YES if the device orientation is portrait, otherwise returns NO.

Availability

Available in iOS 2.0 and later.

Related Sample Code

RosyWriter

Declared In

UIDevice.h

UIDeviceOrientationIsValidInterfaceOrientation

Returns a Boolean value indicating whether the specified orientation constant is valid.

#define UIDeviceOrientationIsValidInterfaceOrientation(orientation) \
   ((orientation) == UIDeviceOrientationPortrait || \
   (orientation) == UIDeviceOrientationPortraitUpsideDown || \
   (orientation) == UIDeviceOrientationLandscapeLeft || \
   (orientation) == UIDeviceOrientationLandscapeRight)

Parameters

orientation: Specify the orientation constant to check.

Return Value

Returns YES if the specified orientation constant is valid or NO if it is not valid.

Availability

Available in iOS 2.0 and later.

Declared In

UIApplication.h

UIEdgeInsetsEqualToEdgeInsets

Compares two edge insets to determine if they are the same.

BOOL UIEdgeInsetsEqualToEdgeInsets (
   UIEdgeInsets insets1,
   UIEdgeInsets insets2
);

Parameters

insets1: An edge inset to compare with insets2.
insets2: An edge inset to compare with insets1.

Return Value

YES if the edge insets are the same; otherwise, NO.

Availability

Available in iOS 2.0 and later.

Declared In

UIGeometry.h

UIEdgeInsetsFromString

Returns a UIKit edge insets structure corresponding to the data in a given string.

UIEdgeInsets UIEdgeInsetsFromString (
   NSString *string
);

Parameters

string: A string whose contents are of the form “{top, left, bottom, right}”, where top, left, bottom, right are the floating-point component values of the UIEdgeInsets structure. An example of a valid string is @”{3.0,8.0,3.0,5.0}”. The string is not localized, so items are always separated with a comma.

Return Value

An edge insets data structure. If the string is not well-formed, the function returns UIEdgeInsetsZero.

Discussion

In general, you should use this function only to convert strings that were previously created using the NSStringFromUIEdgeInsets function.

Availability

Available in iOS 2.0 and later.

Declared In

UIGeometry.h

UIEdgeInsetsInsetRect

Adjusts a rectangle by the given edge insets.

CGRect UIEdgeInsetsInsetRect (
   CGRect rect,
   UIEdgeInsets insets
);

Parameters

rect: The rectangle to be adjusted.
insets: The edge insets to be applied to the adjustment.

Return Value

A rectangle that is adjusted by the UIEdgeInsets structure passed in insets.

Discussion

This inline function increments the origin of rect and decrements the size of rect by applying the appropriate member values of the UIEdgeInsets structure.

Availability

Available in iOS 2.0 and later.

Declared In

UIGeometry.h

UIEdgeInsetsMake

Creates an edge inset for a button or view.

UIEdgeInsets UIEdgeInsetsMake (
   CGFloat top,
   CGFloat left,
   CGFloat bottom,
   CGFloat right
);

Parameters

top: The inset at the top of an object.
left: The inset on the left of an object
bottom: The inset on the bottom of an object.
right: The inset on the right of an object.

Return Value

An inset for a button or view

Discussion

An inset is a margin around the drawing rectangle where each side (left, right, top, and bottom) can have a different value.

Availability

Available in iOS 2.0 and later.

Related Sample Code

UIKit Printing with UIPrintInteractionController and UIViewPrintFormatter

Declared In

UIGeometry.h

UIGraphicsAddPDFContextDestinationAtPoint

Creates a jump destination in the current page.

void UIGraphicsAddPDFContextDestinationAtPoint (
   NSString *name,
   CGPoint point
);

Parameters

name: The name of the destination point. The name you assign is local to the PDF document and is what you use when creating links to this destination.
point: A point on the current page of the PDF context.

Discussion

This function marks the specified point in the current page as the destination of a jump. When the user taps a link that takes them to this jump destination, the PDF document scrolls until the specified point is visible.

If the current graphics context is not a PDF context, this function does nothing.

For information on how to create links to this destination, see the UIGraphicsSetPDFContextDestinationForRect function.

Availability

Available in iOS 3.2 and later.

Declared In

UIGraphics.h

UIGraphicsBeginImageContext

Creates a bitmap-based graphics context and makes it the current context.

void UIGraphicsBeginImageContext (
   CGSize size
);

Parameters

size: The size of the new bitmap context. This represents the size of the image returned by the UIGraphicsGetImageFromCurrentImageContext function.

Discussion

This function is equivalent to calling the UIGraphicsBeginImageContextWithOptions function with the opaque parameter set to NO and a scale factor of 1.0.

In iOS 4 and later, you may call this function from any thread of your app.

Availability

Available in iOS 2.0 and later.

Related Sample Code

Declared In

UIGraphics.h

UIGraphicsBeginImageContextWithOptions

Creates a bitmap-based graphics context with the specified options.

void UIGraphicsBeginImageContextWithOptions(
   CGSize size,
   BOOL opaque,
   CGFloat scale
);

Parameters

size: The size (measured in points) of the new bitmap context. This represents the size of the image returned by the UIGraphicsGetImageFromCurrentImageContext function. To get the size of the bitmap in pixels, you must multiply the width and height values by the value in the scale parameter.
opaque: A Boolean flag indicating whether the bitmap is opaque. If you know the bitmap is fully opaque, specify YES to ignore the alpha channel and optimize the bitmap’s storage. Specifying NO means that the bitmap must include an alpha channel to handle any partially transparent pixels.
scale: The scale factor to apply to the bitmap. If you specify a value of 0.0, the scale factor is set to the scale factor of the device’s main screen.

Discussion

You use this function to configure the drawing environment for rendering into a bitmap. The format for the bitmap is as follows:

For bitmaps created in iOS 3.2 and later, the drawing environment uses the premultiplied ARGB format to store the bitmap data. If the opaque parameter is YES, the bitmap is treated as fully opaque and its alpha channel is ignored.
For bitmaps created in iOS 3.1.x and earlier, the drawing environment uses the premultiplied RGBA format to store the bitmap data.

The environment also uses the default coordinate system for UIKit views, where the origin is in the upper-left corner and the positive axes extend down and to the right of the origin. The supplied scale factor is also applied to the coordinate system and resulting images. The drawing environment is pushed onto the graphics context stack immediately.

While the context created by this function is the current context, you can call the UIGraphicsGetImageFromCurrentImageContext function to retrieve an image object based on the current contents of the context. When you are done modifying the context, you must call the UIGraphicsEndImageContext function to clean up the bitmap drawing environment and remove the graphics context from the top of the context stack. You should not use the UIGraphicsPopContext function to remove this type of context from the stack.

In most other respects, the graphics context created by this function behaves like any other graphics context. You can change the context by pushing and popping other graphics contexts. You can also get the bitmap context using the UIGraphicsGetCurrentContext function.

In iOS 4 and later, you may call this function from any thread of your app.

Availability

Available in iOS 4.0 and later.

Related Sample Code

Declared In

UIGraphics.h

UIGraphicsBeginPDFContextToData

Creates a PDF-based graphics context that targets the specified mutable data object.

void UIGraphicsBeginPDFContextToData (
   NSMutableData *data,
   CGRect bounds,
   NSDictionary *documentInfo
);

Parameters

data

The data object to receive the PDF output data.

bounds

A rectangle that specifies the default size and location of PDF pages. (This value is used as the default media box for each new page.) The origin of the rectangle should typically be (0, 0). Specifying an empty rectangle (CGRectZero) sets the default page size to 8.5 by 11 inches (612 by 792 points).

documentInfo

A dictionary that specifies additional information to be associated with the PDF file. You can use these keys to specify additional metadata and security information for the PDF, such as the author of the PDF or the password for accessing it. The keys in this dictionary are the same keys you pass to the CGPDFContextCreate function and are described in the Auxiliary Dictionary Keys section of CGPDFContext Reference. The dictionary is retained by the new context, so on return you may safely release it.

Specify nil if you do not want to associate any additional information with the PDF document.

Discussion

After creating the graphics context, this function makes it the current drawing context. Any subsequent drawing commands are therefore captured and turned into PDF data. When you are done drawing, you must call the UIGraphicsEndPDFContext function to close the PDF graphics context.

You can use all of the same drawing routines that you would normally use to draw the contents of your application. The graphics context converts all drawing commands into PDF drawing commands automatically. However, before you issue any drawing commands to a PDF context, you must start a new page by calling the UIGraphicsBeginPDFPage or UIGraphicsBeginPDFPageWithInfo function. You can also use these functions to define additional pages later.

After creating it, you can get the PDF context using the UIGraphicsGetCurrentContext function.

Availability

Available in iOS 3.2 and later.

Declared In

UIGraphics.h

UIGraphicsBeginPDFContextToFile

Creates a PDF-based graphics context that targets a file at the specified path.

BOOL UIGraphicsBeginPDFContextToFile (
   NSString *path,
   CGRect bounds,
   NSDictionary *documentInfo
);

Parameters

path

A POSIX-style path string identifying the location of the resulting PDF file. The specified path may be relative or a full path name. If a file does not exist at the specified path, one is created; otherwise, the contents of any existing file are deleted. The directories in the path must exist.

bounds

documentInfo

Specify nil if you do not want to associate any additional information with the PDF document.

Return Value

YES if the PDF context was created successfully or NO if it was not.

Discussion

You can use all of the same drawing routines that you would normally use to draw the contents of your application. However, before you issue any drawing commands to a PDF context, you must start a new page by calling the UIGraphicsBeginPDFPage or UIGraphicsBeginPDFPageWithInfo function. You can also use these functions to define additional pages later.

After creating it, you can get the PDF context using the UIGraphicsGetCurrentContext function.

Availability

Available in iOS 3.2 and later.

Declared In

UIGraphics.h

UIGraphicsBeginPDFPage

Marks the beginning of a new page in a PDF context and configures it using default values.

void UIGraphicsBeginPDFPage (
   void
);

Discussion

This function ends any previous page before beginning a new one. It sets the media box of the new page to the rectangle you specified when you created the PDF context.

If the current graphics context is not a PDF context, this function does nothing.

You must call this function or the UIGraphicsBeginPDFPageWithInfo function before you issue any drawing commands.

Availability

Available in iOS 3.2 and later.

Declared In

UIGraphics.h

UIGraphicsBeginPDFPageWithInfo

Marks the beginning of a new page in a PDF context and configures it using the specified values.

void UIGraphicsBeginPDFPageWithInfo (
   CGRect bounds,
   NSDictionary *pageInfo
);

Parameters

bounds

A rectangle that specifies the size and location of the new PDF page. This rectangle corresponds to the media box rectangle for the page.

pageInfo

A dictionary that specifies additional page-related information, such as the boxes that define different parts of the page. For a list of keys you can include in this dictionary, see Box Dictionary Keys in CGPDFContext Reference. The dictionary is retained by the new page, so you may release it after this function returns.

Specify nil if you do not want to associate any additional information with the page.

Discussion

This function ends any previous page before beginning a new one. It sets the media box of the new page to the value in the kCGPDFContextMediaBox key of the pageInfo dictionary, or to the value in the bounds parameter if the dictionary does not contain the key.

If the current graphics context is not a PDF context, this function does nothing.

You must call this function or the UIGraphicsBeginPDFPageWithInfo function before you issue any drawing commands.

Availability

Available in iOS 3.2 and later.

Declared In

UIGraphics.h

UIGraphicsEndImageContext

Removes the current bitmap-based graphics context from the top of the stack.

void UIGraphicsEndImageContext (
   void
);

Discussion

You use this function to clean up the drawing environment put in place by the UIGraphicsBeginImageContext function and to remove the corresponding bitmap-based graphics context from the top of the stack. If the current context was not created using the UIGraphicsBeginImageContext function, this function does nothing.

In iOS 4 and later, you may call this function from any thread of your app.

Availability

Available in iOS 2.0 and later.

Related Sample Code

Declared In

UIGraphics.h

UIGraphicsEndPDFContext

Closes a PDF graphics context and pops it from the current context stack.

void UIGraphicsEndPDFContext (
   void
);

Discussion

You must call this function after you finish drawing to a PDF graphics context. This function closes the current open page and removes the PDF context from the graphics context stack. It also releases the CGContextRef associated with the PDF context. If the current graphics context is not a PDF context, this function does nothing.

Availability

Available in iOS 3.2 and later.

Declared In

UIGraphics.h

UIGraphicsGetCurrentContext

Returns the current graphics context.

CGContextRef UIGraphicsGetCurrentContext (
   void
);

Return Value

The current graphics context.

Discussion

The current graphics context is nil by default. Prior to calling its drawRect: method, view objects push a valid context onto the stack, making it current. If you are not using a UIView object to do your drawing, however, you must push a valid context onto the stack manually using the UIGraphicsPushContext function.

In iOS 4 and later, you may call this function from any thread of your app.

Availability

Available in iOS 2.0 and later.

Related Sample Code

Declared In

UIGraphics.h

UIGraphicsGetImageFromCurrentImageContext

Returns an image based on the contents of the current bitmap-based graphics context.

UIImage * UIGraphicsGetImageFromCurrentImageContext (
   void
);

Return Value

A image object containing the contents of the current bitmap graphics context.

Discussion

You should call this function only when a bitmap-based graphics context is the current graphics context. If the current context is nil or was not created by a call to UIGraphicsBeginImageContext, this function returns nil.

In iOS 4 and later, you may call this function from any thread of your app.

Availability

Available in iOS 2.0 and later.

Related Sample Code

Declared In

UIGraphics.h

UIGraphicsGetPDFContextBounds

Returns the current page bounds.

CGRect UIGraphicsGetPDFContextBounds (
   void
);

Return Value

The current page bounds associated with the PDF context or CGRectZero if the current context is not a PDF context.

Discussion

If a page has not yet been started, this function returns the default media box you specified when you created the PDF context; otherwise, it returns the page bounds for the current page.

Availability

Available in iOS 3.2 and later.

Declared In

UIGraphics.h

UIGraphicsPopContext

Removes the current graphics context from the top of the stack, restoring the previous context.

void UIGraphicsPopContext (
   void
);

Discussion

Use this function to balance calls to the UIGraphicsPushContext function.

In iOS 4 and later, you may call this function from any thread of your app.

Availability

Available in iOS 2.0 and later.

Declared In

UIGraphics.h

UIGraphicsPushContext

Makes the specified graphics context the current context.

void UIGraphicsPushContext (
   CGContextRef context
);

Parameters

context: The graphics context to make the current context.

Discussion

You can use this function to save the previous graphics state and make the specified context the current context. You must balance calls to this function with matching calls to the UIGraphicsPopContext function.

In iOS 4 and later, you may call this function from any thread of your app.

Availability

Available in iOS 2.0 and later.

Declared In

UIGraphics.h

UIGraphicsSetPDFContextDestinationForRect

Links a rectangle on the current page to the specified jump destination.

void UIGraphicsSetPDFContextDestinationForRect (
   NSString *name,
   CGRect rect
);

Parameters

name: A named destination in the PDF document. This is the same name you used when creating the jump destination using the UIGraphicsAddPDFContextDestinationAtPoint function.
rect: A rectangle on the current page of the PDF context.

Discussion

You use this function to create live links within a PDF document. Tapping the specified rectangle in the PDF document causes the document to display the contents at the associated jump destination.

If the current graphics context is not a PDF context, this function does nothing.

Availability

Available in iOS 3.2 and later.

Declared In

UIGraphics.h

UIGraphicsSetPDFContextURLForRect

Links a rectangle on the current page to the specified URL.

void UIGraphicsSetPDFContextURLForRect (
   NSURL *url,
   CGRect rect
);

Parameters

url: The URL to open.
rect: A rectangle on the current page of the PDF context.

Discussion

You use this function to create external links within a PDF document. If the URL you specify is a type handled by a different application, tapping the rectangle opens that application.

If the current graphics context is not a PDF context, this function does nothing.

Availability

Available in iOS 3.2 and later.

Declared In

UIGraphics.h

UIImageJPEGRepresentation

Returns the data for the specified image in JPEG format.

NSData * UIImageJPEGRepresentation (
   UIImage *image,
   CGFloat compressionQuality
);

Parameters

image: The original image data.
compressionQuality: The quality of the resulting JPEG image, expressed as a value from 0.0 to 1.0. The value 0.0 represents the maximum compression (or lowest quality) while the value 1.0 represents the least compression (or best quality).

Return Value

A data object containing the JPEG data, or nil if there was a problem generating the data. This function may return nil if the image has no data or if the underlying CGImageRef contains data in an unsupported bitmap format.

Discussion

If the image object’s underlying image data has been purged, calling this function forces that data to be reloaded into memory.

Availability

Available in iOS 2.0 and later.

Declared In

UIImage.h

UIImagePNGRepresentation

Returns the data for the specified image in PNG format

NSData * UIImagePNGRepresentation (
   UIImage *image
);

Parameters

image: The original image data.

Return Value

A data object containing the PNG data, or nil if there was a problem generating the data. This function may return nil if the image has no data or if the underlying CGImageRef contains data in an unsupported bitmap format.

Discussion

If the image object’s underlying image data has been purged, calling this function forces that data to be reloaded into memory.

Availability

Available in iOS 2.0 and later.

Related Sample Code

Declared In

UIImage.h

UIImageWriteToSavedPhotosAlbum

Adds the specified image to the user’s Camera Roll album.

void UIImageWriteToSavedPhotosAlbum (
   UIImage  *image,
   id       completionTarget,
   SEL      completionSelector,
   void     *contextInfo
);

Parameters

image

The image to write to the Camera Roll album.

completionTarget

Optionally, the object whose selector should be called after the image has been written to the Camera Roll album.

completionSelector

The method selector, of the completionTarget object, to call. This optional method should conform to the following signature:

- (void)               image: (UIImage *) image

    didFinishSavingWithError: (NSError *) error

                 contextInfo: (void *) contextInfo;

contextInfo

An optional pointer to any context-specific data that you want passed to the completion selector.

Discussion

When used with an image picker controller, you would typically call this function within your imagePickerController:didFinishPickingMediaWithInfo: delegate method implementation.

The use of the completionTarget, completionSelector, and contextInfo parameters is optional and necessary only if you want to be notified asynchronously when the function finishes writing the image to the user’s Camera Roll or Saved Photos album. If you do not want to be notified, pass nil for these parameters.

When used on an iOS device without a camera, this method adds the image to the Saved Photos album rather than to the Camera Roll album.

Availability

Available in iOS 2.0 and later.

Declared In

UIImagePickerController.h

UIInterfaceOrientationIsLandscape

Returns a Boolean value indicating whether the user interface is currently presented in a landscape orientation.

#define UIInterfaceOrientationIsLandscape(orientation) \
   ((orientation) == UIInterfaceOrientationLandscapeLeft || \
   (orientation) == UIInterfaceOrientationLandscapeRight)

Parameters

orientation: Specify the orientation constant to check.

Return Value

Returns YES if the interface orientation is landscape, otherwise returns NO.

Discussion

The interface orientation can be different than the device orientation. You typically use this macro in your view controller code to check the current orientation.

Availability

Available in iOS 2.0 and later.

Related Sample Code

Declared In

UIApplication.h

UIInterfaceOrientationIsPortrait

Returns a Boolean value indicating whether the user interface is currently presented in a portrait orientation.

#define UIInterfaceOrientationIsPortrait(orientation) \
   ((orientation) == UIInterfaceOrientationPortrait || \
   (orientation) == UIInterfaceOrientationPortraitUpsideDown)

Parameters

orientation: Specify the orientation constant to check.

Return Value

Returns YES if the interface orientation is portrait, otherwise returns NO.

Discussion

The interface orientation can be different than the device orientation. You typically use this macro in your view controller code to check the current orientation.

Availability

Available in iOS 2.0 and later.

Related Sample Code

Declared In

UIApplication.h

UIOffsetEqualToOffset

Returns a Boolean value that indicates whether two offsets are equal.

BOOL UIOffsetEqualToOffset(UIOffset offset1, UIOffset offset2) {
   return offset1.horizontal == offset2.horizontal &&
   offset1.vertical == offset2.vertical;
}

Parameters

offset1: The offset to compare with offset2.
offset2: The offset to compare with offset1.

Return Value

YES if offset1 and offset2 are equal, otherwise NO.

Availability

Available in iOS 5.0 and later.

Declared In

UIGeometry.h

UIOffsetFromString

Returns a UIKit offset structure corresponding to the data in a given string.

UIOffset UIOffsetFromString(
   NSString *string
);

Parameters

string: A string containing a representation of an offset.

Return Value

An edge insets data structure. If the string is not well-formed, the function returns UIOffsetZero.

Discussion

In general, you should use this function only to convert strings that were previously created using the NSStringFromUIOffset function.

Availability

Available in iOS 5.0 and later.

Declared In

UIGeometry.h

UIOffsetMake

Returns an offset structure from the given components.

UIOffset UIOffsetMake(CGFloat horizontal, CGFloat vertical) {
   UIOffset offset = {horizontal, vertical};
   return offset;
}

Parameters

horizontal: The horizontal offset.
vertical: The vertical offset.

Return Value

An offset structure with offsets horizontal and vertical.

Availability

Available in iOS 5.0 and later.

Declared In

UIGeometry.h

UIRectClip

Modifies the current clipping path by intersecting it with the specified rectangle.

void UIRectClip (
   CGRect rect
);

Parameters

rect: The rectangle to intersect with the clipping region. If the width or height of the rectangle are less than 0, this function does not change the clipping path.

Discussion

Each call to this function permanently shrinks the clipping path of the current graphics context using the specified rectangle. You cannot use this function to expand the clipping region path. If the current graphics context is nil, this function does nothing.

If you need to return the clipping path to its original shape in your drawing code, you should save the current graphics context before calling this function. To save the current state of the graphics context, call the CGContextSaveGState function before making your modifications. When you are ready to restore the original clipping region, you can then use the CGContextRestoreGState function to restore the previous graphics state.

In iOS 4 and later, you may call this function from any thread of your app.

Availability

Available in iOS 2.0 and later.

Related Sample Code

AdvancedTableViewCells

Declared In

UIGraphics.h

UIRectFill

Fills the specified rectangle with the current color.

void UIRectFill (
   CGRect rect
);

Parameters

rect: The rectangle defining the area in which to draw.

Discussion

Fills the specified rectangle using the fill color of the current graphics context and the kCGBlendModeCopy blend mode.

In iOS 4 and later, you may call this function from any thread of your app.

Availability

Available in iOS 2.0 and later.

Related Sample Code

Declared In

UIGraphics.h

UIRectFillUsingBlendMode

Fills a rectangle with the current fill color using the specified blend mode.

void UIRectFillUsingBlendMode (
   CGRect rect,
   CGBlendMode blendMode
);

Parameters

rect: The rectangle defining the area in which to draw.
blendMode: The blend mode to use during drawing.

Discussion

This function draws the rectangle in the current graphics context. If the current graphics context is nil, this function does nothing.

In iOS 4 and later, you may call this function from any thread of your app.

Availability

Available in iOS 2.0 and later.

Declared In

UIGraphics.h

UIRectFrame

Draws a frame around the inside of the specified rectangle.

void UIRectFrame (
   CGRect rect
);

Parameters

rect: The rectangle defining the area in which to draw.

Discussion

This function draws a frame around the inside of rect in the fill color of the current graphics context and using the kCGBlendModeCopy blend mode. The width is equal to 1.0 in the current coordinate system. Since the frame is drawn inside the rectangle, it is visible even if drawing is clipped to the rectangle. If the current graphics context is nil, this function does nothing.

Because this function does not draw directly on the line, but rather inside it, it uses the current fill color (not stroke color) when drawing.

In iOS 4 and later, you may call this function from any thread of your app.

Availability

Available in iOS 2.0 and later.

Related Sample Code

CopyPasteTile

Declared In

UIGraphics.h

UIRectFrameUsingBlendMode

Draws a frame around the inside of a rectangle using the specified blend mode.

void UIRectFrameUsingBlendMode (
   CGRect rect,
   CGBlendMode blendMode
);

Parameters

rect: The rectangle defining the area in which to draw.
blendMode: The blend mode to use during drawing.

Discussion

This function draws a frame around the inside of rect in the fill color of the current graphics context and using the specified blend mode. The width is equal to 1.0 in the current coordinate system. Since the frame is drawn inside the rectangle, it is visible even if drawing is clipped to the rectangle. If the current graphics context is nil, this function does nothing.

Because this function does not draw directly on the line, but rather inside it, it uses the current fill color (not stroke color) when drawing.

In iOS 4 and later, you may call this function from any thread of your app.

Availability

Available in iOS 2.0 and later.

Declared In

UIGraphics.h

UISaveVideoAtPathToSavedPhotosAlbum

Adds the movie at the specified path to the user’s Camera Roll album.

void UISaveVideoAtPathToSavedPhotosAlbum (
   NSString  *videoPath,
   id        completionTarget,
   SEL       completionSelector,
   void      *contextInfo
);

Parameters

videoPath

The filesystem path to the movie file you want to save to the Camera Roll album.

completionTarget

Optionally, the object whose selector should be called after the movie has been written to the Camera Roll album.

completionSelector

The method selector, of the completionTarget object, to call. This optional method should conform to the following signature:

- (void)               video: (NSString *) videoPath

    didFinishSavingWithError: (NSError *) error

                 contextInfo: (void *) contextInfo;

contextInfo

An optional pointer to any context-specific data that you want passed to the completion selector.

Discussion

When used with an image picker controller, you would typically call this function within your imagePickerController:didFinishPickingMediaWithInfo: delegate method implementation.

Before calling this function, call the UIVideoAtPathIsCompatibleWithSavedPhotosAlbum function to determine if it is possible to save movies to the Camera Roll album. For a code example, refer to Camera Programming Topics for iOS.

The use of the completionTarget, completionSelector, and contextInfo parameters is optional and necessary only if you want to be notified asynchronously when the function finishes writing the movie to the user’s Camera Roll or Saved Photos album. If you do not want to be notified, pass nil for these parameters.

When used on an iOS device without a camera, this method adds the movie to the Saved Photos album rather than to the Camera Roll album.

Availability

Available in iOS 3.1 and later.

Declared In

UIImagePickerController.h

UIVideoAtPathIsCompatibleWithSavedPhotosAlbum

Returns a Boolean value indicating whether the specified video can be saved to user’s Camera Roll album.

BOOL UIVideoAtPathIsCompatibleWithSavedPhotosAlbum (
   NSString  *videoPath
);

Parameters

videoPath: The filesystem path to the movie file you want to save.

Return Value

YES if the video can be saved to the Camera Roll album or NO if it cannot.

Discussion

Not all devices are able to play video files placed in the user’s Camera Roll album. Before attempting to save a video, call this function and check its return value to ensure that saving the video is supported for the current device. For a code example, refer to Camera Programming Topics for iOS.

When used on an iOS device without a camera, this method indicates whether the specified movie can be saved to the Saved Photos album rather than to the Camera Roll album.

Availability

Available in iOS 3.1 and later.

Declared In

UIImagePickerController.h

UI_USER_INTERFACE_IDIOM

Returns the interface idiom supported by the current device.

#define UI_USER_INTERFACE_IDIOM() \
   ([[UIDevice currentDevice] respondsToSelector:@selector(userInterfaceIdiom)] ? \
   [[UIDevice currentDevice] userInterfaceIdiom] : \
   UIUserInterfaceIdiomPhone)

Return Value

UIUserInterfaceIdiomPhone if the device is an iPhone or iPod touch or UIUserInterfaceIdiomPad if the device is an iPad.

Availability

Available in iOS 3.2 and later.

Related Sample Code

Declared In

UIDevice.h

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UIKit Function Reference

Overview

Functions by Task

Application Launch

Image Manipulation

Image and Movie Saving

Graphics

PDF Creation

String Conversions

Managing Edge Insets

Managing Offsets

Interface Orientation Macros

Device Orientation Macros

Interface Idiom Macro

Accessibility

Text Manipulations

Functions

CGAffineTransformFromString

Parameters

Return Value

Discussion

Availability

See Also

Declared In

CGPointFromString

Parameters

Return Value

Discussion

Availability

See Also

Declared In

CGRectFromString

Parameters

Return Value

Discussion

Availability

See Also

Declared In

CGSizeFromString

Parameters

Return Value

Discussion

Availability

See Also

Declared In

NSStringFromCGAffineTransform

Parameters

Return Value

Availability

See Also

Declared In

NSStringFromCGPoint

Parameters

Return Value

Availability

See Also

Declared In

NSStringFromCGRect

Parameters

Return Value

Availability

See Also

Related Sample Code

Declared In

NSStringFromCGSize

Parameters

Return Value

Availability

See Also

Declared In

NSStringFromUIEdgeInsets

Parameters

Return Value

Availability

See Also

Declared In

NSStringFromUIOffset

Parameters

Return Value

Availability