[iOS]使用NSProxy實現代理模式

// MyProxy.h

#import
<Foundation/Foundation.h>

@interface MyProxy :
NSProxy {

   
NSObject *object;

}

- (id)transformToObject:(NSObject *)anObject;

@end

// MyProxy.m

#import
"MyProxy.h"

@implementation MyProxy

- (void)dealloc

{

    [object
release];

   
object = nil;

    [super
dealloc];

}

- (void)fun

{

   
// Do someting virtual

    //
先做一些代理工作，然後建立一個後台線程，在後台線程中再調用真正的[object fun];

}

// Stupid transform implementation just by assigning a passed in object as transformation target. You can write your factory here and use passed in object as id for object that need
ot be created.

- (id)transformToObject:(NSObject *)anObject 

{

   
if(object != anObject) {

        [object
release];

    }

   
object = [anObject retain];

   
return object;

}

- (void)forwardInvocation:(NSInvocation *)invocation 

{

   
if (object !=
nil) {

        [invocation
setTarget:object];    

        

        [invocation
invoke];

    }

}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel 

{

   
NSMethodSignature *result;

   
if (object !=
nil) {

        result = [object
methodSignatureForSelector:sel];

    }
else {

       
// Will throw an exception as default implementation

        result = [super
methodSignatureForSelector:sel];

    }

   
return result;

}

@end

// RealSubject.h

#import
<Foundation/Foundation.h>

@implementation RealSubject : NSObject

- (void)fun;

@end

// RealSubject.m

#import
"RealSubject.h"

@implementation RealSubject

- (void)fun

{

    //
這個方法需要代理進行惰性調用

   
// Do something real

}

- (void)otherFun

{

    //
這個方法不需要代理做任何處理，可直接被調用

   
// Do something real

}

@end

// main.m

int main(int argc,
char *argv[]) 

{

   
NSAutoreleasePool * pool = [[NSAutoreleasePool
alloc]
init];

   
MyProxy *myProxy = [MyProxy
alloc];

   
RealSubject *realSub = [[RealSubject
alloc] init];

    [myProxy
transformToObject:realSub];

    [myProxy
fun];
// 直接調用myProxy的fun，執行代理工作

    [myProxy
otherFun];
// 依次調用myProxy的methodSignatureForSelector和forwardInvocation轉寄給realSub，realSub調用otherFun

    [realSubject
release];

    [myProxy
release];

    [pool
release];

   
return 0;

}

注意，調用MyProxy中未定義的方法otherFun會出現'MyProxy' may not respond to 'fun'的警告，可通過使用私人範疇或通過performSelector:withObject:來避免，如果有更好的方法，請告知。