Prism Library UWP Show multiple views for an app

Question

I am trying Show multiple views for an app for Prism Library UWP.

I got System.NullReferenceException for frame.Navigate(typeof(ScreenCapture)); like below:

        async void ExecuteNewWindow()
        {
            CoreApplicationView newView = CoreApplication.CreateNewView();
            int newViewId = 0;
            await newView.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
            {
                Frame frame = new Frame();
                frame.Navigate(typeof(ScreenCapture));
                Window.Current.Content = frame;
                // You have to activate the window in order to show it later.
                Window.Current.Activate();

                newViewId = ApplicationView.GetForCurrentView().Id;
            });
            bool viewShown = await ApplicationViewSwitcher.TryShowAsStandaloneAsync(newViewId);
        }

How to implement multiple view in Prism library for uwp.

Answer 1

Your project is Xamarin.Forms, but the parameter of frame.Navigate(typeof(ScreenCapture)); is uwp Page type. I checked your code, ScreenCapture is Forms ContentPage. For your requirement, you could use Dependency service to call ExecuteNewWindow and place ExecuteNewWindow in UWP project.

Interface

public interface INewPageService
{
     void  CreateNewPage();
}

Implement

[assembly: Dependency(typeof(INewPageService))]

namespace BlankApp1.UWP
{
   public class INewPageServiceImplement : INewPageService
    {
        public async void CreateNewPage()
        {
            CoreApplicationView newView = CoreApplication.CreateNewView();
            int newViewId = 0;
            await newView.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
            {
                Frame frame = new Frame();
                frame.Navigate(typeof(NewPage)); // uwp page
                Window.Current.Content = frame;
                // You have to activate the window in order to show it later.
                Window.Current.Activate();

                newViewId = ApplicationView.GetForCurrentView().Id;
            });
            bool viewShown = await ApplicationViewSwitcher.TryShowAsStandaloneAsync(newViewId);

         }
    }
}

Usage

DependencyService.Get<INewPageService>(DependencyFetchTarget.NewInstance).CreateNewPage();

Please don't forget register it in uwp app.xaml.cs file.

if (rootFrame == null)
{
    // Create a Frame to act as the navigation context and navigate to the first page
    rootFrame = new Frame();

    rootFrame.NavigationFailed += OnNavigationFailed;

    Xamarin.Forms.Forms.Init(e);
    DependencyService.Register<INewPageService, INewPageServiceImplement>();
    if (e.PreviousExecutionState == ApplicationExecutionState.Terminated)
    {
        //TODO: Load state from previously suspended application
    }

    // Place the frame in the current Window
    Window.Current.Content = rootFrame;
}