performSelector:withObject:afterDelay: 精要概览(持续更新)
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- (void)performSelector:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay;
--1--
知识点:这个方法是单线程的,也就是说只有当前调用此方法的函数执行完毕后,selector方法才会被调用。
- (void)mainMethod{ [self performSelector:@selector(delayMethod) withObject:nil afterDelay:1]; NSLog(@"调用方法==开始"); sleep(5); NSLog(@"调用方法==结束");}- (void)delayMethod{ NSLog(@"执行延迟方法");}执行结果(注意log打印的顺序): 调用方法==开始 调用方法==结束 执行延迟方法
实战经验:正因为本方法是一个单线程的,所以有些时候,我们会遇到虽然调用了这个方法,但是不执行的问题。这时,我们需要将原代码改造如下:
改造前代码:无法执行延迟方法
-(void)someMethod{ [self performSelector:@selector(labelDidDisappeared:) withObject:label afterDelay:2]; //因为某些原因,不被调用,没有执行}-(void)labelDidDisappeared:(UILabel *)label{ [label removeFromSuperview]; [label release];}
改造后代码: 可以正常执行延迟方法
-(void)someMethod{ //关键 [self performSelectorOnMainThread:@selector(labelWillDisappeared:) withObject:label waitUntilDone:NO]; } -(void)labelWillDisappeared:(UILabel *)label{ [self performSelector:@selector(labelDidDisappeared:) withObject:label afterDelay:2];}-(void)labelDidDisappeared:(UILabel *)label{ [label removeFromSuperview]; [label release];}
知识扩展:以下两个方法均是多线程方法
- (void)performSelectorInBackground:(SEL)aSelector withObject:(id)arg
和
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait;
参考:http://blog.csdn.net/baxiaxx/article/details/7878338 感谢原作者的无私和奉献!
--2--
知识点:该方法只能接受一个参数。如果需要传递多个参数怎么办呢? 让selector调用的方法接受的参数类型修改为Dictionary类型。
注意:
(1)如果调用的selector不接受参数则,withObject:nil
(2) 通过performSelector:withObjcet:afterDelay调用的方法不能有返回值
知识扩展:performSelector 带多个参数
//第一个试验:带一个参数- (void) fooOneIput:(NSString*) first { NSLog(@"Logs %@", first);}//然后调用它[self performSelector:@selector(fooOneInput:) withObject:@"first"];//第二个试验:带多个参数- (void) fooFirstInput:(NSString*) first secondInput:(NSString*) second { NSLog(@"Logs %@ then %@", first, second);}//然后调用它[self performSelector:@selector(fooFirstInput:secondInput:) withObject:@"first" withObject:@"second"];
实战经验:经实验,只有performSelector: withObject: 方法可以带多个参数,其它类似的perform方法均不行,包括和此方法最类似的performSelectorInBackground:withObject: 方法。
http://www.cnblogs.com/ygm900/archive/2013/07/03/3169706.html- performSelector:withObject:afterDelay: 精要概览(持续更新)
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