performSelectorOnMainThread
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[selfperformSelectorOnMainThread:@selector(fetchedData:) withObject:datawaitUntilDone:YES];
会创建一个新的线程实行fetchedData函数,并传入参数data,并且会等待函数退出后再继续执行。
- (void)fetchedData:(NSData *)responseData {
。。。}
在多线程操作中,有一个著名的错误,叫做“Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread”,一旦出现这个错误,程序会立即crashed。
这是由于,apple不允许程序员在主线程以外的线程中对ui进行操作(Bug?)
而笔者在一次http异步操作中也出现过这个错误。当时使用了NSOperation进行了http异步请求,然后使用kvo模式注册观察者,当数据下载完毕后,在主线程中接收下载完毕的通知,并在observeValueForKeyPath方法中使用[tableview reloadData]更新UI。
这样也导致了上述错误。
解决的方法是使用performSelectorOnMainThread进行ui的更新:
[self performSelectorOnMainThread:@selector(refresh) withObject:nil waitUntilDone:NO];
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