新开网络处理线程 不返回主线程处理UI刷新的报错

This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes. This will cause an exception in a future release.
Stack:(

使用GCD
将网络处理请求放在GCD里处理 返回主线程刷新UI即可

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.



    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSURL *url = [NSURL URLWithString:@"http://img6.faloo.com/Picture/0x0/0/747/747488.jpg"];

        NSURLRequest *request = [NSURLRequest requestWithURL:url];
        NSURLSession *session = [NSURLSession sharedSession];

        NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {


            NSLog(@"request == %@",request);

            NSLog(@"data  == %@",data);

            NSLog(@"response == %@",response);

            NSLog(@"error == %@",error);
            if (error == nil) {

                NSLog(@"===================================================================");
                NSString *dataStr = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
                NSLog(@"dataStr =====>>>  %@ ",dataStr);



                //返回主线程刷新ui
                dispatch_async(dispatch_get_main_queue(), ^{
                    UIImage *image = [UIImage imageWithData:data];

                    _imageView.image = image;

                });
            }

        }];

        [task resume];
    });



}

1. 你首先将工作从主线程移到全局线程。因为这是一个 dispatch_async() ，Block 会被异步地提交，意味着调用线程地执行将会继续。这就使得 viewDidLoad 更早地在主线程完成，让加载过程感觉起来更加快速。
2. 在这里，生成了一个新的图像。既然你要使用此新图像更新你的 UIImageView ，那么你就添加一个新的 Block 到主线程。记住——你必须总是在主线程访问 UIKit 的类。