Error & crash when showing ContentDialog without XamlRoot

[mrlacey]

Describe the bug

ArgumentException is thrown when attempting to open a ContentDialog in a WinUI3 Desktop app when the XamlRoot is not set.
X-Ref docs

Steps to reproduce the bug

1. Create a new blank WinUI3 Desktop app
2. Add this class

public sealed partial class MyCustomDialog : ContentDialog
{
    public MyCustomDialog()
    {
        this.InitializeComponent();
    }
}

3. With this XAML

<ContentDialog
    x:Class="App206.MyCustomDialog"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="TITLE"
    PrimaryButtonText="Button1"
    SecondaryButtonText="Button2">

    <Grid>
        <TextBlock>hello</TextBlock>
    </Grid>
</ContentDialog>

4. Change myButton_Click in MainPage.xaml.cs to be:

private async void myButton_Click(object sender, RoutedEventArgs e)
{
    var dialog = new MyCustomDialog();
    await dialog.ShowAsync();
}

5. Run the app and click the button.

System.ArgumentException
  HResult=0x80070057
  Message=Value does not fall within the expected range.
  Source=WinRT.Runtime
  StackTrace:
   at WinRT.ExceptionHelpers.ThrowExceptionForHR(Int32 hr)
   at ABI.Microsoft.UI.Xaml.Controls.IContentDialog.global::Microsoft.UI.Xaml.Controls.IContentDialog.ShowAsync()
   at Microsoft.UI.Xaml.Controls.ContentDialog.ShowAsync()
   at App206.MainWindow.<myButton_Click>d__1.MoveNext() in C:\Users\matt\source\repos\App206\App206\App206\MainWindow.xaml.cs:line 35

Expected behavior

The dialog will not be be shown because there is no XamlRoot but:

• The app should not crash.
  and/or
• There should be a more descriptive error message displayed indicating the issue.

Screenshots

Version Info

NuGet package version:
Microsoft.WinUI 3.0.0-preview3.201113.0

Windows app type:

UWP	Win32
No	Yes

Windows 10 version	Saw the problem?
Insider Build (20175.1000)	Yes
May 2020 Update (19041)	Yes
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Xbox
Surface Hub
IoT

Additional context

This works without issue in a UWP app (WinUI2 and 3)

[mrlacey]

X-Ref #1679 which discusses other ContentDialog related issues and possible improvements.

[sylveon]

I believe you're forgetting to set the XamlRoot

[mrlacey]

I believe you're forgetting to set the XamlRoot

Yes, this was the issue.

Will update the OP to reflect the need not to crash and provide a more descriptive error message.

[github-actions]

This issue is stale because it has been open 180 days with no activity. Remove stale label or comment or this will be closed in 5 days.

[mrlacey]

At the very least this needs a more helpful error message.

This gives no clue as to the cause and so doesn't help solve the cause of the crash.

System.ArgumentException - Message=Value does not fall within the expected range.

[nickrandolph]

Let's bump the priority on this issue - it's seriously nuts that developers have to set xamlroot on a dialog.