ios - 需要有关 dispatch_sync 和 dispatch_async 的帮助

Question

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {

    [self dismissViewControllerAnimated:YES completion:^{}];

    [self.navigationController.tabBarController.view addSubview:self.waitingView];

    dispatch_queue_t currentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(currentQueue, ^{

        self.originalImgFromPicker = [info objectForKey:UIImagePickerControllerOriginalImage];

        CGSize size = self.originalImgFromPicker.size;
        if (size.width > 320)
        {
            size.height /= (size.width / 320);
            size.width = 320;
        }

        UIGraphicsBeginImageContext(size);
        [self.originalImgFromPicker drawInRect:CGRectMake(0,0,size.width,size.height)];
        self.resizedImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        self.originalImgFromPicker = nil;

        NSData *resizedImageBinary = UIImageJPEGRepresentation(self.resizedImage, 1.0);

        self.resizedImageBinaryString = [NSString base64StringFromData:resizedImageBinary length:resizedImageBinary.length];

        dispatch_sync(currentQueue, ^{
            [self.waitingView removeFromSuperview];
        });
    });
}

我正在处理图像，在此期间我使用带有事件指示器的透明 View 来阻止 UI。

但是这个 self.waitingView 消失需要很长时间才能消失。

当图像处理正在进行时，UI 实际上被 self.waitingView 阻止，这意味着当我尝试点击背后的控件时没有任何效果，但是当异步 block 中的图像处理完成时 self。 waitingView 仍保留在屏幕上，当我尝试点击任何控件时它会响应。

如果我什么都不做，它需要一些时间才能消失。

我想以快速的方式执行此操作，我在代码中做错了什么？

Answer 1

UI操作应该在主队列中完成

修改代码

         dispatch_sync(currentQueue, ^{
            [self.waitingView removeFromSuperview];
        });

到

        dispatch_sync(dispatch_get_main_queue(), ^{
            [self.waitingView removeFromSuperview];
        });

所以你的方法应该是这样的

    - (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {

    [self dismissViewControllerAnimated:YES completion:^{}];

    [self.navigationController.tabBarController.view addSubview:self.waitingView];

    dispatch_queue_t currentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(currentQueue, ^{

        self.originalImgFromPicker = [info objectForKey:UIImagePickerControllerOriginalImage];

        CGSize size = self.originalImgFromPicker.size;
        if (size.width > 320)
        {
            size.height /= (size.width / 320);
            size.width = 320;
        }

        UIGraphicsBeginImageContext(size);
        [self.originalImgFromPicker drawInRect:CGRectMake(0,0,size.width,size.height)];
        self.resizedImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        self.originalImgFromPicker = nil;

        NSData *resizedImageBinary = UIImageJPEGRepresentation(self.resizedImage, 1.0);

        self.resizedImageBinaryString = [NSString base64StringFromData:resizedImageBinary length:resizedImageBinary.length];

        dispatch_sync(dispatch_get_main_queue(), ^{
            [self.waitingView removeFromSuperview];
        });
    });
}