Before you get started, we recommend you have a look at Microsoft's comprehensive guide on Customizing a ContentPage. It is important that you understand how Xamarin renders the same page on different platforms using ContentPage , ExportRenderer and PageRenderer . In this guide, you will learn how to create a fully featured document viewer and editor as page renderer on each platform.
Complete sample code can be found here:
The rendering process can be taken advantage of to implement platform-specific customization by creating a custom renderer for a ContentPage on each platform. The process for doing this is as follows:
An unaltered ContentPage can be added to the shared Xamarin.Forms project, as shown in the following XAML code example:
ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="CustomRenderer.AdvancedViewerPage" Title="Advanced Viewer Page"> ContentPage.Content> ContentPage.Content> ContentPage>
Similarly, the code-behind file for the ContentPage should also remain unaltered, as shown in the following code example:
public partial class AdvancedViewerPage : ContentPage public AdvancedViewerPage() // Document viewer contains toolbar, let's hide the global one NavigationPage.SetHasNavigationBar(this, false); InitializeComponent(); > >
An instance of the AdvancedViewerPage will be used to display document viewer on each platform. Customization of the control will be carried out in the custom renderer, so no additional implementation is required in the AdvancedViewerPage class.
The empty AdvancedViewerPage must be displayed by the Xamarin.Forms application. This occurs when a button on the MainPage instance is tapped, which in turn executes the OnOpenAdvancedViewerButtonClicked method, as shown in the following code example:
async void OnOpenAdvancedViewerButtonClicked(object sender, EventArgs e) await Navigation.PushAsync(new AdvancedViewerPage()); >
This code simply navigates to the AdvancedViewerPage , on which custom renderers will customize the page's appearance on each platform.
The AdvancedViewerPage instance is rendered by platform-specific AdvancedViewerPageRenderer classes, which all derive from the PageRenderer class for that platform. This results in each AdvancedViewerPage instance being rendered with document viewer, as shown in the following GIF:
The following code example shows the page renderer for the iOS platform:
[assembly: ExportRenderer(typeof(AdvancedViewerPage), typeof(AdvancedViewerPageRenderer))] namespace CustomRenderer.iOS public class AdvancedViewerPageRenderer : PageRenderer private PTTabbedDocumentViewController mTabViewController; protected override void OnElementChanged(VisualElementChangedEventArgs e) base.OnElementChanged(e); if (e.OldElement != null || Element == null) return; > try SetupUserInterface(); SetupEventHandlers(); > catch (Exception ex) System.Diagnostics.Debug.WriteLine(@" ERROR: ", ex.Message); > > //. > >
where the document viewer can be setup as follows:
void SetupUserInterface() mTabViewController = new PTTabbedDocumentViewController(); UINavigationController navigationController = new UINavigationController(mTabViewController); AddChildViewController(navigationController); View.AddSubview(navigationController.View); navigationController.DidMoveToParentViewController(this); NSUrl fileURL = NSBundle.MainBundle.GetUrlForResource("sample", "pdf"); mTabViewController.OpenDocumentWithURL(fileURL); >
The following code example shows the page renderer for the Android platform:
[assembly: ExportRenderer(typeof(AdvancedViewerPage), typeof(AdvancedViewerPageRenderer))] namespace CustomRenderer.Droid public class AdvancedViewerPageRenderer : PageRenderer private DocumentView mDocumentView; public ViewerPageRenderer(Context context) : base(context) > protected override void OnElementChanged(ElementChangedEventArgsPage> e) base.OnElementChanged(e); if (e.OldElement != null || Element == null) return; > try SetupUserInterface(); SetupEventHandlers(); AddView(view); > catch (Exception ex) System.Diagnostics.Debug.WriteLine(@" ERROR: ", ex.Message); > > //. > >
where the document viewer can be setup as follows:
void SetupUserInterface() activity = this.Context as Activity; view = activity.LayoutInflater.Inflate(Resource.Layout.AdvancedViewerLayout, this, false); mDocumentView = view.FindViewByIdDocumentView>(Resource.Id.document_view); var context = this.Context; FragmentManager childManager = null; if (context is AppCompatActivity) var activity = context as AppCompatActivity; var manager = activity.SupportFragmentManager; var fragments = manager.Fragments; if (fragments.Count > 0) childManager = fragments[0].ChildFragmentManager; > if (childManager != null) mDocumentView.OpenDocument(GetFile(), "", GetConfig(), childManager); > > >
The document viewer is highly customizable and can be configured to remove/modify many components.
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