UWP create new window for each file opened

Question

I'm trying to make an app open a window for each file.

-- Code ---

App.cs:

    protected async override void OnFileActivated(FileActivatedEventArgs Args)
    {
        //Opens Main Page
        base.OnFileActivated(Args);
        var RF = new Frame();
        var MW = new MainPage();
        AppWindow appWindow = await AppWindow.TryCreateAsync();
        var TB = appWindow.TitleBar;
        RF.Navigate(typeof(MainPage), Args);
        ElementCompositionPreview.SetAppWindowContent(appWindow, RF);
        appWindow.Equals(MW);
        Window.Current.Equals(MW);
        await appWindow.TryShowAsync();
        TB.ButtonHoverBackgroundColor = Colors.White;
        TB.ButtonHoverForegroundColor = Colors.Black;
        TB.ButtonBackgroundColor = Colors.Transparent;
        TB.ButtonPressedBackgroundColor = Colors.WhiteSmoke;
        TB.ButtonPressedForegroundColor = Colors.Black;
        TB.ButtonInactiveBackgroundColor = Colors.Transparent;
        TB.ButtonInactiveForegroundColor = Color.FromArgb(1, 3, 165, 252);
        TB.ExtendsContentIntoTitleBar = true;
        Window.Current.Activate();
    }

MainPage.cs:

    protected override async void OnNavigatedTo(NavigationEventArgs EvArgs)
    {
        //File opened arguments
        base.OnNavigatedTo(EvArgs);
        var Args = EvArgs.Parameter as IActivatedEventArgs;
        var FArgs = Args as FileActivatedEventArgs;
        string Value = GetText(REB);
        string SecValue = GetText(RTB);
        if (Args != null)
        {
            //Check if the app is opened by file
            if (Args.Kind == ActivationKind.File)
            {
                //Set file content
                TXTFile = FArgs.Files[0] as StorageFile;
                if (Value == "")
                {
                    var Str = await TXTFile.OpenReadAsync();
                    ContentDialog ED2 = FileSaveDialog;
                    ED2.PrimaryButtonClick += ED2_PrimaryButtonClick;
                    void ED2_PrimaryButtonClick(ContentDialog Sender, ContentDialogButtonClickEventArgs DialogEvArgs)
                    {
                        //Save the file if it isn't saved
                        Save();
                    }
                    ED2.SecondaryButtonClick += ED2_SecondaryButtonClick;
                    void ED2_SecondaryButtonClick(ContentDialog Sender, ContentDialogButtonClickEventArgs DialogEvArgs)
                    {
                        //Don't save the file
                        //Set document content
                        REB.Document.LoadFromStream(TextSetOptions.FormatRtf, Str);
                        RTB.Document.LoadFromStream(TextSetOptions.FormatRtf, Str);
                        Str.Dispose();
                    }
                    ED2.CloseButtonClick += ED2_CloseButtonClick;
                    void ED2_CloseButtonClick(ContentDialog Sender, ContentDialogButtonClickEventArgs DialogEvArgs)
                    {
                        //Cancel the action
                    }
                    await ED2.ShowAsync();
                    Str.Dispose();
                }
                else
                {
                    //Set document content
                    var Str = await TXTFile.OpenReadAsync();
                    REB.Document.LoadFromStream(TextSetOptions.FormatRtf, Str);
                    RTB.Document.LoadFromStream(TextSetOptions.FormatRtf, Str);
                    Str.Dispose();
                }
            }
        }
        else
        {
            //If there are no arguments, the file, and the RichEditBox should both remain empty 
        }
    }

    public string GetText(RichEditBox RichEditor)
    {
        RichEditor.Document.GetText(TextGetOptions.FormatRtf, out string Text);
        var Range = RichEditor.Document.GetRange(0, Text.Length);
        Range.GetText(TextGetOptions.FormatRtf, out string Value);
        return Value;
    }

Note:

• the GetText method used is equivalent to RichEditBox.Document.GetText(TextGetOptions.FormatRtf, out string Value);
• REB is the main workspace for the user to type in
• RTB is the box that is compared with REB to see if the contents are saved or not (if the contents are saved, the GetText method should return their values equal)

Expected behavior: If the app has a window active with text, the app should open a file on double click in a secondary window. Else, if the text is equal to "", the app should replace it with whatever is in the file.

Actual behavior: The app overrides the text, crashes, makes windows randomly, or creates black windows that can only be killed with Task Manager or Visual Studio

Answer 1

I'm not sure what is the file type that you are using so I didn't check the text part. But I have to say that the way you are creating a new window is not correct. If you want to open a new window every time when you open a new file, you don't have to call Window.Current.Activate(); every time. I've made a simple demo that you could check.

In App.xaml.cs:

   protected async override void OnFileActivated(FileActivatedEventArgs args)
    {
        Frame rootFrame = Window.Current.Content as Frame;

        // Do not repeat app initialization when the Window already has content,
        // just ensure that the window is active
        if (rootFrame == null)
        {
            // Create a Frame to act as the navigation context and navigate to the first page
            rootFrame = new Frame();
            // Place the frame in the current Window
            Window.Current.Content = rootFrame;

            rootFrame.Navigate(typeof(MainPage), args.Files);

            Window.Current.Activate();
        }
        else 
        {
            AppWindow appWindow = await AppWindow.TryCreateAsync();

            Frame appWindowContentFrame = new Frame();
            appWindowContentFrame.Navigate(typeof(MainPage),args.Files);

            ElementCompositionPreview.SetAppWindowContent(appWindow, appWindowContentFrame);

            await appWindow.TryShowAsync();
        }
    }

When you launch the app for the first time, you should go through the normal launch process. When the app is launched more than onetime, then you could create a new window with AppWindow.

In MainPage.cs

  protected override void OnNavigatedTo(NavigationEventArgs e)
    {
        // this is the file you need
        var d = e.Parameter;
    }

You could try this code first to make sure that your window is created and shown correctly.