NSProxy

Inherits From:
none (NSProxy is a root class)

Conforms To:
NSObject

Declared In:
Foundation/NSProxy.h

Class Description

NSProxy implements the basic methods required of a root class, including those defined in the NSObject protocol. However, as an abstract class it doesn't provide an initialization method, and it raises an exception upon receiving any message it doesn't respond to. A concrete subclass must therefore provide an initialization or creation method and override the forwardInvocation: and methodSignatureForSelector: methods to handle messages that it doesn't implement itself. A subclass's implementation of forwardInvocation: should do whatever is needed to process the invocation, such as forwarding the invocation over the network or loading the real object and passing it the invocation. methodSignatureForSelector: is required to provide argument type information for a given message; a subclass's implementation should be able to determine the argument types for the messages it needs to forward and should construct an NSMethodSignature accordingly. See the NSDistantObject, NSInvocation, and NSMethodSignature class specifications for more information.

Adopted Protocols

NSObject

- autorelease

- class

- conformsToProtocol:

- description

- hash

- isEqual:

- isKindOfClass:

- isMemberOfClass:

- isProxy

- performSelector:

- performSelector:withObject:

- performSelector:withObject:withObject:

- release

- respondsToSelector:

- retain

- retainCount

- self

- superclass

- zone

Creating instances

+ alloc

+ allocWithZone:

Deallocating instances

- dealloc

Getting the class

+ class

Handling unimplemented methods

- forwardInvocation:

- methodSignatureForSelector:

Getting a description

- description

Class Methods

alloc

Returns a new instance of the receiving class, as described in the NSObject class specification under the alloc class method.

allocWithZone:

Returns a new instance of the receiving class, as described in the NSObject class specification under the allocWithZone: class method.

class

Returns self. Since this is a class method, it returns the class object.

See also: + class (NSObject), - class (NSObject protocol)

load

This method is invoked whenever a class or category is added to the Objective-C runtime; implement this method to perform class-specific behavior upon loading. It is sent to classes and categories that are both dynamically loaded and statically linked, but only if the newly-loaded class or category implements a method that can respond. As an example, when Interface Builder loads a palette, the load method is sent to each class and category in the palette.

load is usually invoked before initialize. It is usually the very first method sent to the class, although this isn't guaranteed. The order in which classes are loaded is also not guaranteed, to the point that superclasses aren't even guaranteed to be loaded before all of their subclasses. Because you can't rely on other classes being loaded at the point when your class is sent a load message, you should be extremely careful when messaging other classes from within your load method.

Note that although load is essentially replaces NEXTSTEP's finishLoading: method, the circumstances surrounding their invocation is slightly different. Consult your NEXTSTEP Developer documentation if you are porting code that uses finishLoading:.

See also: + load (NSObject)

respondsToSelector:

Returns YES if the receiving class responds to aSelector messages, NO otherwise.

Instance Methods

class

- (Class)class

Returns the class of the receiver (not the class of the real object).

conformsToProtocol:

- (BOOL)conformsToProtocol:(Protocol)aProtocol

Uses forwardInvocation: to send the conformsToProtocol: message to the real object and returns the result. Note that NSProxy's implementation of forwardInvocation: merely raises an exception.

dealloc

Deallocates the memory occupied by the receiver, as described in the NSObject class specification under the dealloc instance method.

description

Returns an NSString containing the real class name and the id of the receiver as a hexadecimal number.

forwardInvocation:

Passes anInvocation on to the real object that the proxy represents. NSProxy's implementation merely raises NSInvalidArgumentException. Override this method in your subclass to handle anInvocation appropriately, at the very least by setting its return value.

For example, if your proxy merely forwards messages to an instance variable named realObject, it can implement forwardInvocation: like this:

- (void)forwardInvocation:(NSInvocation *)anInvocation
{
    [anInvocation setTarget:realObject];
    [anInvocation invoke];
    return;
}

isKindOfClass:

- (BOOL)isKindOfClass:(Class)aClass

Uses forwardInvocation: to send the isKindOfClass: message to the real object and returns the result. Note that NSProxy's implementation of forwardInvocation: merely raises an exception.

isMemberOfClass:

- (BOOL)isMemberOfClass:(Class)aClass

Uses forwardInvocation: to send the isMemberOfClass: message to the real object and returns the result. Note that NSProxy's implementation of forwardInvocation: merely raises an exception.

isProxy

- (BOOL)isProxy

Returns YES. Subclasses shouldn't override this method to return NO.

methodSignatureForSelector:

Raises NSInvalidArgumentException. Override this method in your concrete subclass to return a proper NSMethodSignature for aSelector and the class that your proxy objects stand in for. Be sure to avoid an infinite loop when necessary by checking that aSelector isn't the selector for this method itself and by not sending any message that might invoke this method.

For example, if your proxy merely forwards messages to an instance variable named realObject, it can implement methodSignatureForSelector: like this:

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector
{
    return [realObject methodSignatureForSelector:aSelector];
}

See also: - methodSignatureForSelector: (NSObject)

respondsToSelector:

- (BOOL)respondsToSelector:(SEL)aSelector

Uses forwardInvocation: to send the respondsToSelector: message to the real object and returns the result. Note that NSProxy's implementation of forwardInvocation: merely raises an exception.

Copyright © 1997, Apple Computer, Inc. All rights reserved.