从模式页面（表单）调用时未显示 Xamarin Forms iOS UIImagePickerController答案

【问题标题】：Xamarin Forms iOS UIImagePickerController not shown when called from a modal page (formsheet)从模式页面（表单）调用时未显示 Xamarin Forms iOS UIImagePickerController
【发布时间】：2021-07-12 19:59:28
【问题描述】：

我目前正在尝试让这个示例工作： https://docs.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/dependency-service/photo-picker

但是在 iOS 上，UIImagePickerController 没有出现。我已经想通了，这是因为调用页面是一个模态页面（FormSheet）。我为模态页面设置了这个属性。

<Style x:Key="ModalPageStyle" TargetType="ContentPage" BasedOn="{StaticResource DefaultPageStyle}">
        <Setter Property="Shell.PresentationMode" Value="ModalAnimated" />
        <Setter Property="ios:Page.ModalPresentationStyle" Value="FormSheet" />
    </Style>

当我将页面改回正常页面时（通过删除Style），UIImagePickerController 工作正常。但是我需要从模态页面调用它。

我已经尝试将根 ViewController 设置为全屏。

public Task<Stream> GetImageStreamAsync()
        {
            // Create and define UIImagePickerController
            imagePicker = new UIImagePickerController
            {
                SourceType = UIImagePickerControllerSourceType.PhotoLibrary,
                MediaTypes = UIImagePickerController.AvailableMediaTypes(UIImagePickerControllerSourceType.PhotoLibrary),
                ModalPresentationStyle = UIModalPresentationStyle.FormSheet,
            };

            // Set event handlers
            imagePicker.FinishedPickingMedia += OnImagePickerFinishedPickingMedia;
            imagePicker.Canceled += OnImagePickerCancelled;

            // Present UIImagePickerController;
            UIWindow window = UIApplication.SharedApplication.KeyWindow;
            var viewController = window.RootViewController;
            if(viewController.ModalPresentationStyle != UIModalPresentationStyle.FullScreen)
                viewController.ModalPresentationStyle = UIModalPresentationStyle.FullScreen;

            viewController.PresentViewController(imagePicker, true, null);

            // Return Task object
            taskCompletionSource = new TaskCompletionSource<Stream>();
            return taskCompletionSource.Task;
        }

但是结果是一样的。无论如何都可以从模态页面显示UIImagePickerController？

【问题讨论】：

您一次只能在 ViewController 上显示一个模式。您需要调用 PresentViewController，而不是在 RootViewController 上，而是在您现在显示的模式（您的表单）上。
感谢您的帮助，我会试试这个并报告。

标签： ios xamarin uiimagepickercontroller

【解决方案1】：

感谢@Cheesebaron，我可以解决这个问题。这对我有用。

public Task<Stream> GetImageStreamAsync()
        {
            // Create and define UIImagePickerController
            imagePicker = new UIImagePickerController
            {
                SourceType = UIImagePickerControllerSourceType.PhotoLibrary,
                MediaTypes = UIImagePickerController.AvailableMediaTypes(UIImagePickerControllerSourceType.PhotoLibrary),
                //ModalPresentationStyle = UIModalPresentationStyle.FormSheet,
            };

            // Set event handlers
            imagePicker.FinishedPickingMedia += OnImagePickerFinishedPickingMedia;
            imagePicker.Canceled += OnImagePickerCancelled;

            // Present UIImagePickerController;
            UIViewController currentController = UIApplication.SharedApplication.KeyWindow.RootViewController;
            while (currentController.PresentedViewController != null)
                currentController = currentController.PresentedViewController;
   
            currentController.PresentViewController(imagePicker, true, null);

            // Return Task object
            taskCompletionSource = new TaskCompletionSource<Stream>();
            return taskCompletionSource.Task;
        }

感谢您的帮助！

【讨论】：