System.ArgumentException: 'Value does not fall within the expected range.' on Content Dialog

Question

I'm triyng to make a login system in my UWP (WinUI3) app and when I try to lauch de Login Content Dialog it crashes throwing this error:

System.ArgumentException: 'Value does not fall within the expected range.'

on await messageDialog.ShowAsync();

Code on app.xaml.cs:

protected override async void OnLaunched(Microsoft.UI.Xaml.LaunchActivatedEventArgs args)
{

    m_window = new MainWindow();
    m_window.Activate();

    Login();

}

protected async void Login()
{
    var messageDialog = new ContentDialogs.LoginDialog();
    await messageDialog.ShowAsync();

    if (App.Aplicacao.Utilizador == null)
    {
        m_window.Close();
        return;
    }
}

Content Dialog XAML:

<ContentDialog
    x:Class="xizSoft.ContentDialogs.LoginDialog"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:xizSoft.ContentDialogs"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Background="{ThemeResource SystemControlAcrylicWindowBrush}">

    <Grid>
    </Grid>
</ContentDialog>

Code-behind:

public LoginDialog()
{
    this.InitializeComponent();
}

Answer 1

Wait until the contents of the window has been loaded and set the XamlRoot property of the ContentDialog.

This is how you would display the dialog on startup:

protected override async void OnLaunched(Microsoft.UI.Xaml.LaunchActivatedEventArgs args)
{
    m_window = new MainWindow();
    m_window.Activate();

    if (m_window.Content is FrameworkElement fe)
        fe.Loaded += (ss, ee) => Login();
}

protected void Login()
{
    var messageDialog = new ContentDialogs.LoginDialog();
    messageDialog.XamlRoot = m_window.Content.XamlRoot;
    await messageDialog.ShowAsync();

    if (App.Aplicacao.Utilizador == null)
    {
        m_window.Close();
        return;
    }
}

private Window m_window;