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NSURLConnection和NSRunLoop


主线程中创建一个NSURLConnection并异步运行

[self performSelectorOnMainThread:@selector(start) withObject:nil waitUntilDone:YES];
- (void)start
{
    //step 1:请求地址
    NSURL *url = [NSURL URLWithString:@"www.2cto.com"];
    //step 2:实例化一个request
    NSURLRequest *request =[NSURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:30.0];
    //step 3:创建链接
    self.connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];//直接执行了
    if (self.connection) {
        NSLog(@"链接成功");
    }else {
        NSLog(@"链接失败");
    }
}

问题:
当前线程是主线程
创建的NSURLConnection实例执行在主线程。主线程有一个执行的runloop实例来支持NSURLConnection的异步执行,
此时runloop的执行模式为NSDefaultRunLoopMode,这样的mode下,假设主线程执行拖动操作,runloop不处理NSURLConnection的回调事件。
由于拖动操作发生过程中。使当前线程的runloop执行在UITrackingRunLoopMode模式下,这样的模式下的runloop会暂定处理其它事件(异步请求回调、timer事件等)。


解决方法,改动代码为:

[self performSelectorOnMainThread:@selector(start) withObject:nil waitUntilDone:YES];
- (void)start
{
    //step 1:请求地址
    NSURL *url = [NSURL URLWithString:@"www.2cto.com"];
    //step 2:实例化一个request
    NSURLRequest *request =[NSURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:30.0];
    //step 3:创建链接
    self.connection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];//临时不执行
    [connection scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];//用NSRunLoopCommonModes
    [connection start];    
    if (self.connection) {
        NSLog(@"链接成功");
    }else {
        NSLog(@"链接失败");
    }
}





NSURLConnection和NSRunLoop