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");
    }
}

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");
    }
}