[摘要]在 iOS中可以直接调用某个对象的消息方式有两种，其中一种就是NSInvocation，本文介绍IOS NSInvocation用法，并提供简单的示例代码供参考。
在 iOS中可以直接调用某个对象的消息方式有两种：
一种是performSelector:withObject；
再一种就是NSInvocation。
第一种方式比较简单，能完成简单的调用。但是对于>2个的参数或者有返回值的处理，那就需要做些额外工作才能搞定。那么在这种情况下，我们就可以使用NSInvocation来进行这些相对复杂的操作。
main.h
| 1 | #import <Foundation/Foundation.h> |
| 2 | #import "MyClass.h" |
| 3 | |
| 4 | int main (int argc, const char * argv[]) |
| 5 | { |
| 6 | |
| 7 | NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; |
| 8 | |
| 9 | MyClass *myClass = [[MyClass alloc] init]; |
| 10 | NSString *myString = @"My string"; |
| 11 | |
| 12 | //普通调用 |
| 13 | NSString *normalInvokeString = [myClass appendMyString:myString]; |
| 14 | NSLog(@"The normal invoke string is: %@", normalInvokeString); |
| 15 | |
| 16 | //NSInvocation调用 |
| 17 | SEL mySelector = @selector(appendMyString:); |
| 18 | NSMethodSignature * sig = [[myClass class] |
| 19 | instanceMethodSignatureForSelector: mySelector]; |
| 20 | |
| 21 | NSInvocation * myInvocation = [NSInvocation invocationWithMethodSignature: sig]; |
| 22 | [myInvocation setTarget: myClass]; |
| 23 | [myInvocation setSelector: mySelector]; |
| 24 | |
| 25 | [myInvocation setArgument: &myString atIndex: 2]; |
| 26 | |
| 27 | NSString * result = nil; |
| 28 | [myInvocation retainArguments]; |
| 29 | [myInvocation invoke]; |
| 30 | [myInvocation getReturnValue: &result]; |
| 31 | NSLog(@"The NSInvocation invoke string is: %@", result); |
| 32 | |
| 33 | [myClass release]; |
| 34 | |
| 35 | [pool drain]; |
| 36 | return 0; |
| 37 | } |
MyClass.h
| 1 | #import <Foundation/Foundation.h> |
| 2 | |
| 3 | |
| 4 | @interface MyClass : NSObject { |
| 5 | } |
| 6 | |
| 7 | - (NSString *)appendMyString:(NSString *)string; |
| 8 | |
| 9 | @end |
MyClass.m
| 1 | #import "MyClass.h" |
| 2 | |
| 3 | |
| 4 | @implementation MyClass |
| 5 | |
| 6 | - (id)init |
| 7 | { |
| 8 | self = [super init]; |
| 9 | if (self) { |
| 10 | // Initialization code here. |
| 11 | } |
| 12 | |
| 13 | return self; |
| 14 | } |
| 15 | |
| 16 | - (NSString *)appendMyString:(NSString *)string |
| 17 | { |
| 18 | NSString *mString = [NSString stringWithFormat:@"%@ after append method", string]; |
| 19 | |
| 20 | return mString; |
| 21 | } |
| 22 | |
| 23 | - (void)dealloc |
| 24 | { |
| 25 | [super dealloc]; |
| 26 | } |
| 27 | |
| 28 | @end |
这里说明一下[myInvocation setArgument: &myString atIndex: 2];为什么index从2开始 ，原因为：0 1 两个参数已经被target 和selector占用。