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

直接上代码

main.h

#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

#import <Foundation/Foundation.h>


@interface MyClass : NSObject {

}

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

@end

MyClass.m

#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