Crash on WinUI 3 with ObservableCollection<> binded to ItemsSource, only in Release mode

Question

In my WinUI 3 app, I get no errors when the app is in Debug mode, but when I turn the Release mode, I get a System.NullReferenceException.

Looking at the stack it seems to me that the problem is related to the TreeView and the ItemsSource binding.

stack detail

Here is the XAML I use to produce the exception:

<?xml version="1.0" encoding="utf-8"?>
<Window
    x:Class="App1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:App1"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Title="App1">

    <StackPanel Orientation="Vertical">
        <TreeView ItemsSource="{x:Bind Menu}" />
    </StackPanel>
</Window>

and the code behind:

namespace App1;

/// <summary>
/// An empty window that can be used on its own or navigated to within a Frame.
/// </summary>
public sealed partial class MainWindow : Window
{
    public MainWindow()
    {
        this.InitializeComponent();
    }

    public ObservableCollection<MenuItemViewModel> Menu { get; set; } = new ObservableCollection<MenuItemViewModel>();
}

public class MenuItemViewModel
{
    public string Title { get; set; }
}

The Microsoft.WindowsAppSDK is Version="1.6.250228001"

I tried the following combinations of ItemsControl and collections:

TreeView+ ObservableCollection<>, the exception is raised in Release mode,
TreeView+ List<>, the exception is not raised
ListView + ObservableCollection<>, the exception is raised in Release mode,
ListView + List<>, the exception is not raised

What am I missing?

You could take a look at Andrew's solution about this.

Luting
– Luting

2025-03-25 07:09:22 +00:00
Commented Mar 25 at 7:09 — Luting
– Luting, Commented Mar 25 at 7:09

Andrew KeepCoding · Accepted Answer · 2025-03-18 04:37:17Z

1

It seems that you are hitting this.

Enabling AllowUnsafeBlocks:

<AllowUnsafeBlocks>true</AllowUnsafeBlocks>

or installing Microsoft.Windows.CSWinRT (v2.2.0 or later) NuGet package should fix your issue.

edited Mar 18 at 4:37

answered Mar 14 at 0:55

Andrew KeepCoding

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