最近有人问NSInvocation怎么用，于是写了个NSInvocation的小例子

转自：http://blog.csdn.net/volcan1987/article/details/6690208

直接上代码

main.h

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#import <Foundation/Foundation.h>

#import "MyClass.h"



int main (int argc, const char * argv[])

{



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



MyClass *myClass = [[MyClass alloc] init];

NSString *myString = @"My string";



//普通调用

NSString *normalInvokeString = [myClass appendMyString:myString];

NSLog(@"The normal invoke string is: %@", normalInvokeString);



//NSInvocation调用

SEL mySelector = @selector(appendMyString:);

NSMethodSignature * sig = [[myClass class]

instanceMethodSignatureForSelector: mySelector];



NSInvocation * myInvocation = [NSInvocation invocationWithMethodSignature: sig];

[myInvocation setTarget: myClass];

[myInvocation setSelector: mySelector];



[myInvocation setArgument: &myString atIndex: 2];



NSString * result = nil;

[myInvocation retainArguments];

[myInvocation invoke];

[myInvocation getReturnValue: &result];

NSLog(@"The NSInvocation invoke string is: %@", result);



[myClass release];



[pool drain];

return 0;

}

MyClass.h

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#import <Foundation/Foundation.h>





@interface MyClass : NSObject {



}



- (NSString *)appendMyString:(NSString *)string;



@end

MyClass.m

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#import "MyClass.h"





@implementation MyClass



- (id)init

{

self = [super init];

if (self) {

// Initialization code here.

}



return self;

}



- (NSString *)appendMyString:(NSString *)string

{

NSString *mString = [NSString stringWithFormat:@"%@ after append method", string];



return mString;

}



- (void)dealloc

{

[super dealloc];

}



@end

这里说明一下[myInvocation setArgument: &myString atIndex: 2];为什么index从2开始

文档中的说明

Indices 0 and 1 indicate the hidden arguments self and _cmd, respectively; you should set these values directly with the setTarget: and setSelector: methods. Use indices 2 and greater for the arguments normally passed in a message.意思就是0和1是隐藏参数，而这两个参数是要在setTarget和setSelector设置的，所以我们调用方法中的参数就要从2开始了，如果有多个参数，那么就依次递增，ok，就写这么多