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