I’ve been a WPF developer for about 10 years now, and I’ve seen a lot of idiocy from it in all shapes and sizes, but today I just stumbled upon a fresh batch of male cow manure that just absolutely takes the cake. Every cake in existence, actually.

Putting a converter at the top of a Window’s resources list somehow breaks resources of UI objects that come after it.

Here is the simplest example of an application that reproduces this issue, with the least amount of code I can muster:

<Window x:Class="WpfApp1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:converters="clr-namespace:WpfApp1.Converters"
        xmlns:system="clr-namespace:System;assembly=mscorlib"
        SizeToContent="WidthAndHeight"
        WindowStartupLocation="CenterScreen">
    <Window.Resources>
        <converters:BaseConverter x:Key="test"/>

        <Grid x:Key="TestItemTemplateGrid" x:Shared="false">
            <Button Content="{Binding StringFormat='Button {0}'}" Width="300"/>
        </Grid>
    </Window.Resources>

    <ItemsControl>
        <system:Int32>0</system:Int32>
        <system:Int32>1</system:Int32>
        <system:Int32>2</system:Int32>
        <system:Int32>3</system:Int32>
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <ContentControl Content="{StaticResource TestItemTemplateGrid}" Margin="0,5,0,0"/>
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>
</Window>

The converter:

using System;
using System.Globalization;
using System.Windows.Data;
using System.Windows.Markup;

namespace WpfApp1.Converters
{
    public class BaseConverter : MarkupExtension, IValueConverter
    {
        public virtual object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return Binding.DoNothing;
        }

        public virtual object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return Binding.DoNothing;
        }

        public override object ProvideValue(IServiceProvider serviceProvider)
        {
            return this;
        }
    }
}

This is just a simple attempt to load a variable amount of items inside an ItemsControl, where each item is a ContentControl that populates itself to be a Grid defined in a resource.

This is what the app is supposed to look like based on this xaml:

But here is what it actually looks like:

It’s like the x:Shared is breaking and becoming true or something, just because a converter resource came before it.

Things I’ve tested:

• The converter’s key name doesn’t matter
• The converter’s type and/or method implementations don’t matter
• The ItemsControl having a bound ItemsSource vs hard-coded entries doesn’t matter
• The actual content inside the Grid doesn’t matter

Of course, removing the <converters:BaseConverter x:Key="test"/> fixes it, but here’s the real kicker: Putting it last in the resources list instead ALSO fixes it.

…Wow. Just, wow. What is this? Am I dead? Am I dreaming? Is April fools day programmed into WPF, but it’s bugged (like everything else) and came a month late? Can someone explain this? I’m losing my mind here.

The project file, in case it matters:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net5.0-windows</TargetFramework>
    <UseWPF>true</UseWPF>
  </PropertyGroup>

</Project>