Weird XAML errors after upgrading WPF app to .NET 5 - wpf

Question

I have a XAML view that I created in a .NET Framework WPF app, and I'm trying to upgrade the app to .NET 5:
<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:AutoPBW="clr-namespace:AutoPBW;assembly=AutoPBW"
xmlns:scm="clr-namespace:System.ComponentModel;assembly=WindowsBase"
xmlns:shell="clr-namespace:System.Windows.Shell;assembly=PresentationFramework"
mc:Ignorable="d"
x:Name="window"
x:Class="AutoPBW.WPF.MainWindow"
Title="AutoPBW" Height="397" Width="653" Loaded="window_Loaded" Closing="window_Closing" Icon="AutoPBW.ico">
<Window.Resources>
<!-- this CollectionViewSource gives a null reference exception on the d:DesignSource attribute -->
<CollectionViewSource x:Key="playerGameViewSource" d:DesignSource="{d:DesignInstance {x:Type AutoPBW:PlayerGame}, CreateList=True}"/>
<Style x:Key="ListItemStyle" TargetType="{x:Type ListBoxItem}">
<Style.Resources>
</Style.Resources>
<Setter Property="Template">
<Setter.Value>
<!-- this ControlTempate gives an error saying that the Item.MouseOver.Background resource could not be found -->
<ControlTemplate TargetType="{x:Type ListBoxItem}">
<Border x:Name="Bd" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Padding="{TemplateBinding Padding}" SnapsToDevicePixels="true">
<ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
</Border>
<ControlTemplate.Triggers>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="IsMouseOver" Value="True"/>
</MultiTrigger.Conditions>
<!-- here is where the Item.MouseOver.Background resource is actually referenced -->
<Setter Property="Background" TargetName="Bd" Value="{StaticResource Item.MouseOver.Background}"/>
<Setter Property="BorderBrush" TargetName="Bd" Value="{StaticResource Item.MouseOver.Border}"/>
</MultiTrigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
<Grid>
<!-- this is where the actual UI is defined, no errors here -->
</Grid>
</Window>
I have removed a few irrelevant sections, but the comments denote where I encountered compile errors.
The errors I see are:
XDG0062 Object not set to an instance of an object.
and
XDG0062 Cannot find resource named 'Item.MouseOver.Background'. Resource names are case sensitive.
How can I solve these errors?
Thanks! 🙂

Answer 1

Oh, I figured it out. I had my TargetFramework set incorrectly in my project file. It should have been net5-windows, but I had it set to net5.0-windows.