Xamarin QLPreviewController + NavigationPage 在 iOS 10 上损坏

Question

将设备更新到iOS10后，QLPreviewController停止正确显示文档。它显示白色屏幕。我已经从应用程序中提取了示例场景。

它包含带有两个按钮的单页，应该加载两个不同的文档：

<?xml version="1.0" encoding="utf-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
        xmlns:local="clr-namespace:QuickLookIOS10Test"
        x:Class="QuickLookIOS10Test.QuickLookIOS10TestPage">
    <StackLayout Orientation="Vertical">
        <Button Text="Load first doc" Clicked="OnLoadFirstClicked"/>
        <Button Text="Load second doc" Clicked="OnLoadSecondClicked"/>
        <Button Text="Navigate forward" Clicked="OnForwardClicked"/>

        <local:QLDocumentView
            x:Name="DocumentView"
            BackgroundColor="Silver"
            HorizontalOptions="FillAndExpand"
            VerticalOptions="FillAndExpand"/>
    </StackLayout>
</ContentPage>

其中：

public class QLDocumentView : View
{
    public static readonly BindableProperty FilePathProperty =
        BindableProperty.Create(nameof(FilePath), typeof(string), typeof(QLDocumentView), null);

    public string FilePath
    {
        get { return (string)GetValue(FilePathProperty); }
        set { SetValue(FilePathProperty, value); }
    }
}

涉及自定义渲染器：

public class QLDocumentViewRenderer : ViewRenderer<QLDocumentView, UIView>
{
    private QLPreviewController controller;

    public override SizeRequest GetDesiredSize(double widthConstraint, double heightConstraint)
    {
        //This is a fix to prevent incorrect scaling after rotating from portrait to landscape.
        //No idea why does this work :( Bug #101639
        return new SizeRequest(Size.Zero, Size.Zero);
    }

    protected override void OnElementChanged(ElementChangedEventArgs<QLDocumentView> e)
    {
        base.OnElementChanged(e);

        if (Control == null)
        {
            controller = new QLPreviewController();
            SetNativeControl(controller.View);
        }

        RefreshView();
    }

    protected override void OnElementPropertyChanged(object sender,
                                                     System.ComponentModel.PropertyChangedEventArgs e)
    {
        base.OnElementPropertyChanged(sender, e);

        if (e.PropertyName == QLDocumentView.FilePathProperty.PropertyName)
        {
            RefreshView();
        }
    }

    private void RefreshView()
    {
        DisposeDataSource();

        if (Element?.FilePath != null)
        {
            controller.DataSource = new DocumentQLPreviewControllerDataSource(Element.FilePath);
        }

        controller.ReloadData();
    }

    protected override void Dispose(bool disposing)
    {
        base.Dispose(disposing);

        if (disposing)
        {
            DisposeDataSource();
            DisposeController();
        }
    }

    private void DisposeDataSource()
    {
        var dataSource = controller.DataSource;
        controller.DataSource = null;
        dataSource?.Dispose();
    }

    private void DisposeController()
    {
        controller?.Dispose();
        controller = null;
    }

    private class DocumentQLPreviewControllerDataSource : QLPreviewControllerDataSource
    {
        private readonly string fileName;

        public DocumentQLPreviewControllerDataSource(string fileName)
        {
            this.fileName = fileName;
        }

        public override nint PreviewItemCount(QLPreviewController controller)
        {
            return 1;
        }

        public override IQLPreviewItem GetPreviewItem(QLPreviewController controller, nint index)
        {
            NSUrl url = NSUrl.FromFilename(fileName);
            return new QlItem(url);
        }

        private sealed class QlItem : QLPreviewItem
        {
            private readonly NSUrl itemUrl;

            public QlItem(NSUrl uri)
            {
                itemUrl = uri;
            }

            public override string ItemTitle { get { return string.Empty; } }

            public override NSUrl ItemUrl { get { return itemUrl; } }

            protected override void Dispose(bool disposing)
            {
                base.Dispose(disposing);

                if (disposing)
                {
                    this.itemUrl?.Dispose();
                }
            }
        }
    }
}

如果应用程序设置主页面如下：

MainPage = new NavigationPage(new QuickLookIOS10TestPage());

它在 iOS 9.3 上有效，但在 iOS 10 上无效。如果我删除 NavigationPage:

MainPage = new QuickLookIOS10TestPage();

它适用于两个 iOS 版本。

按钮点击背后的代码只是设置控件的文件路径属性。

Sample app demonstrating the problem

Xamarin 表单 2.3.2.127

Xamarin Studio 6.1.1（内部版本 15）

Answer 1

我遇到过同样的问题。在iOS10中的QuickLook中看起来像something was changed or even broken，但解决方案很简单：

public class PdfViewerControlRenderer : ViewRenderer<PdfViewerControl, UIView>
{
    private readonly bool IsOniOS10;

    private UIViewController _controller;
    private QLPreviewController _qlPreviewController;

    public PdfViewerControlRenderer()
    {
        IsOniOS10 = UIDevice.CurrentDevice.CheckSystemVersion(10, 0);
    }

    protected override void OnElementChanged(ElementChangedEventArgs<PdfViewerControl> e)
    {
        if (e.NewElement != null)
        {
            _controller = new UIViewController();
            _qlPreviewController = new QLPreviewController();

            //...
            // Set QuickLook datasource here
            //...

            if (!IsOniOS10)
            {
                _controller.AddChildViewController(_qlPreviewController);
                _controller.View.AddSubview(_qlPreviewController.View);
                _qlPreviewController.DidMoveToParentViewController(_controller);
            }
            SetNativeControl(_controller.View);
        }
    }

    public override void LayoutSubviews()
    {
        base.LayoutSubviews();
        _controller.View.Frame = Bounds;
        _controller.View.AutoresizingMask = UIViewAutoresizing.FlexibleWidth | UIViewAutoresizing.FlexibleHeight;
        _qlPreviewController.View.Frame = Bounds;
        if (IsOniOS10)
        {
            _controller.View.AddSubview(_qlPreviewController.View);
            _qlPreviewController.DidMoveToParentViewController(_controller);
        }
    }
}

结果：

Xamarin QLPreviewController + NavigationPage 在 iOS 10 上损坏

Xamarin QLPreviewController + NavigationPage broken on iOS 10

quicklook

xamarin.ios

xamarin.forms