未调用dismissViewController完成处理程序

Question

尝试使用链接中第一个答案中的代码（由 Kampai 提供）： How to use UIAlertController to replace UIActionSheet?

但是，在我的代码中甚至没有调用完成处理程序。

按下两个按钮后可以解除警报操作表，但完成处理程序内部没有任何工作。知道可能是什么问题吗？我是使用完成处理程序的新手，并试图在网上找到答案，但很少有人遇到与我相同的问题。

- (IBAction)takePhotoButtonPressed:(UIButton *)sender {
pressedButtonTagNumber = sender.tag;

UIAlertController *actionSheet = [UIAlertController alertControllerWithTitle:nil message:nil preferredStyle:UIAlertControllerStyleActionSheet];

[actionSheet addAction:[UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {

    // Cancel button tappped
    [self dismissViewControllerAnimated:YES completion:^{
    }];
}]];

[actionSheet addAction:[UIAlertAction actionWithTitle:@"Take a Photo" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
    NSLog(@"!");
    // Take a Photo button tapped
    [self dismissViewControllerAnimated:YES completion:^{
        NSLog(@"0"); // NOT CALLED
        // Initialize UIImagePickerController
        UIImagePickerController *takePhotoImagePickerController = [[UIImagePickerController alloc] init];            takePhotoImagePickerController.delegate = self;
        takePhotoImagePickerController.allowsEditing = YES;
        NSLog(@"1");
        // Check and assign image source
        if (![UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) {
            NSLog(@"2");
            UIAlertController *noCameraErrorSheet = [UIAlertController alertControllerWithTitle:@"Camera is not available" message:nil preferredStyle:UIAlertControllerStyleActionSheet];
            [noCameraErrorSheet addAction:[UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {
                // Cancel button tappped
                [self dismissViewControllerAnimated:YES completion:^{
                }];
            }]];
        } else {
            takePhotoImagePickerController.sourceType = UIImagePickerControllerSourceTypeCamera;
            // Present UIImagePickerController
            [self presentViewController:takePhotoImagePickerController animated:YES completion:NULL];
        }

    }];
}]];

解决方案：

@Paulw11 解决方案效果很好：

1) 无需为 UIAlertController 解除 ViewController。2）如果包装它正在解散（显然），则无法调用新的 UIAlertController 。3) 最好提前检查和禁用按钮。

UIAlertController *actionSheet = [UIAlertController alertControllerWithTitle:nil message:nil preferredStyle:UIAlertControllerStyleActionSheet];

[actionSheet addAction:[UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {
}]];

UIAlertAction *takePhotoActionButton = [UIAlertAction actionWithTitle:@"Take Photo" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
    [self takePhoto];
}];
UIAlertAction *uploadPhotoActionButton = [UIAlertAction actionWithTitle:@"Upload from Library" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
    [self uploadPhoto];
}];

// Disable take a photo button if source not available
if (![UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) {
    [takePhotoActionButton setEnabled:FALSE];
}
// Disable upload a photo button if source not available
if (![UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypePhotoLibrary]) {
    [uploadPhotoActionButton setEnabled:FALSE];
}

[actionSheet addAction:takePhotoActionButton];
[actionSheet addAction:uploadPhotoActionButton];

// Present action sheet.
[self presentViewController:actionSheet animated:YES completion:nil];

Answer 1

您不需要dismissViewController:animated:从操作处理程序中调用来删除警报。 UIAlertController在调用动作处理程序代码之前调用它来解除自身。

在您的操作处理程序中，您只需执行选择该操作时应该执行的任何操作：

在这种情况下：

• 在您的取消操作中，您无需执行任何操作
• 在你的“拍照”动作中，你拍照

此外，从用户体验的角度来看，最好禁用“拍照”或在他们选择后立即显示警报，而不是在他们尝试拍照后发出警报；换句话说，早点而不是晚点指出问题