IOS NSInvocation用法简介-转
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
#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 ,原因为:0 1 两个参数已经被target 和selector占用。