Unable to Cast error when using <Style TargetType=

Question

I'm attempting to use a resource dictionary and the style TargetType property to change the look of the buttons in my solution. I am receiving a cast error at run time when the first button is loaded. Everything is working fine if I manually set the style in the button's properties, but the point is to change the look of all the buttons, not one at a time.

Here's the relevant exception:

System.Windows.Markup.XamlParseException occurred
  HResult=-2146233087
  Message='Initialization of 'System.Windows.Controls.Button' threw an exception.' Line number '6' and line position '72'.
  Source=PresentationFramework
  LineNumber=6
  LinePosition=72
  StackTrace:
       at System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, IXamlObjectWriterFactory writerFactory, Boolean skipJournaledProperties, Object rootObject, XamlObjectWriterSettings settings, Uri baseUri)
       at System.Windows.Markup.WpfXamlLoader.LoadBaml(XamlReader xamlReader, Boolean skipJournaledProperties, Object rootObject, XamlAccessLevel accessLevel, Uri baseUri)
       at System.Windows.Markup.XamlReader.LoadBaml(Stream stream, ParserContext parserContext, Object parent, Boolean closeStream)
       at System.Windows.Application.LoadComponent(Object component, Uri resourceLocator)
       at WpfTestApplication.Views.MainWindow.InitializeComponent() in d:\TFSC\CUDL\Research\Chris.Dailey\WpfTestApplication\WpfTestApplication\Views\MainWindow.xaml:line 1
       at WpfTestApplication.Views.MainWindow..ctor() in d:\TFSC\CUDL\Research\Chris.Dailey\WpfTestApplication\WpfTestApplication\Views\MainWindow.xaml.cs:line 28
  InnerException: System.InvalidCastException
       HResult=-2147467262
       Message=Unable to cast object of type 'MS.Internal.NamedObject' to type 'System.Windows.FrameworkTemplate'.
       Source=PresentationFramework
       StackTrace:
            at System.Windows.Controls.Control.OnTemplateChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
            at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
            at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
            at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
            at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
            at System.Windows.StyleHelper.ApplyStyleOrTemplateValue(FrameworkObject fo, DependencyProperty dp)
            at System.Windows.StyleHelper.InvalidateContainerDependents(DependencyObject container, FrugalStructList`1& exclusionContainerDependents, FrugalStructList`1& oldContainerDependents, FrugalStructList`1& newContainerDependents)
            at System.Windows.StyleHelper.DoStyleInvalidations(FrameworkElement fe, FrameworkContentElement fce, Style oldStyle, Style newStyle)
            at System.Windows.StyleHelper.UpdateStyleCache(FrameworkElement fe, FrameworkContentElement fce, Style oldStyle, Style newStyle, Style& styleCache)
            at System.Windows.FrameworkElement.OnStyleChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
            at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
            at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
            at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
            at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
            at System.Windows.DependencyObject.InvalidateProperty(DependencyProperty   dp, Boolean preserveCurrentValue)
            at System.Windows.FrameworkElement.UpdateStyleProperty()
            at System.Windows.FrameworkElement.OnInitialized(EventArgs e)
            at System.Windows.FrameworkElement.TryFireInitialized()
            at System.Windows.FrameworkElement.EndInit()
            at MS.Internal.Xaml.Runtime.ClrObjectRuntime.InitializationGuard(XamlType xamlType, Object obj, Boolean begin)
       InnerException: 

Here's the relevant code. The Resource Dictionary:

    <ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">    <Style TargetType="{x:Type Button}">
    <Style TargetType="{x:Type Button}">
        <Setter Property="Control.Template" Value="{StaticResource ButtonTemplate}"
    </Style>
    <ControlTemplate x:Key="ButtonTemplate" TargetType="{x:Type Button}">
        <Border Name="Border" BorderBrush="Orange" BorderThickness="3" CornerRadius="3" Background="Red" TextBlock.Foreground="White">
            <Grid>
                <Rectangle Name="FocusCue" Visibility="Hidden" Stroke="Black" StrokeThickness="1" StrokeDashArray="1 2" SnapsToDevicePixels="True" ></Rectangle>
                <ContentPresenter RecognizesAccessKey="True" Margin="{TemplateBinding Padding}"></ContentPresenter>
            </Grid>
        </Border>
        <ControlTemplate.Triggers>
            <Trigger Property="IsMouseOver" Value="True">
                <Setter TargetName="Border" Property="Background" Value="DarkRed" />
            </Trigger>
            <Trigger Property="IsPressed" Value="True">
                <Setter TargetName="Border" Property="Background" Value="IndianRed" />
                <Setter TargetName="Border" Property="BorderBrush" Value="DarkKhaki" />
            </Trigger>
            <Trigger Property="IsKeyboardFocused" Value="True">
                <Setter TargetName="FocusCue" Property="Visibility" Value="Visible" />
            </Trigger>
            <Trigger Property="IsEnabled" Value="False">
                <Setter TargetName="Border" Property="TextBlock.Foreground" Value="Gray" />
                <Setter TargetName="Border" Property="Background" Value="MistyRose" />
            </Trigger>
        </ControlTemplate.Triggers>
    </ControlTemplate>
</ResourceDictionary>

The main window:

<Window x:Class="WpfTestApplication.Views.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
<WrapPanel>
    <Button x:Name="ButtonGradient" Click="ButtonGradient_OnClick">Gradient</Button>
    <Button x:Name="ButtonDrawing" Click="ButtonDrawing_OnClick">Drawing</Button>
    <Button x:Name="ButtonEventTester"  Click="ButtonEventTester_OnClick">Event Tester</Button>
    <Button x:Name="ButtonCommandTester"  Style="{x:Null}" Command="New">Execute a Command</Button>
</WrapPanel>

I would appreciate any input on what might be causing this. The outer error is completely useless, and I don't know enough about this to understand why a casting error might be occuring.

Answer 1

In Xaml code, order matters. Place your template above the style that references it.

When working with WPF resources, remember to declare the resources in the correct order.

A style or template that is referenced elsewhere must be defined before it can be used. In other words, if Style1 uses BrushA as a StaticResource, then BrushA must be defined before Style1. Otherwise, you’ll get fun errors like:

Unable to cast object of type 'MS.Internal.NamedObject' to type 'System.Windows.FrameworkTemplate'

Answer 2

I had a similar problem and it turned out that my style was using StaticResource instead of DynamicResource. http://blog.alner.net/archive/2010/05/07/wpf-style-and-template-resources_order-matters.aspx

Answer 3

Using VS2012 and your style above, I was able to successfully apply your ControlTemplate. I did wrap it in a Style first, but that's more a matter of preference.

The only other difference is that I had to guess what you did for your Border since that was not included.

The style below worked flawlessly at both design-time and run-time:

<Style TargetType="{x:Type Button}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type Button}">
                <Border Name="Border" Background="LightBlue">
                    <Grid>
                        <Rectangle Name="FocusCue" Visibility="Hidden" Stroke="Black" StrokeThickness="1" StrokeDashArray="1 2" SnapsToDevicePixels="True" ></Rectangle>
                        <ContentPresenter RecognizesAccessKey="True" Margin="{TemplateBinding Padding}"></ContentPresenter>
                    </Grid>
                </Border>
                <ControlTemplate.Triggers>
                    <Trigger Property="IsMouseOver" Value="True">
                        <Setter TargetName="Border" Property="Background" Value="DarkRed" />
                    </Trigger>
                    <Trigger Property="IsPressed" Value="True">
                        <Setter TargetName="Border" Property="Background" Value="IndianRed" />
                        <Setter TargetName="Border" Property="BorderBrush" Value="DarkKhaki" />
                    </Trigger>
                    <Trigger Property="IsKeyboardFocused" Value="True">
                        <Setter TargetName="FocusCue" Property="Visibility" Value="Visible" />
                    </Trigger>
                    <Trigger Property="IsEnabled" Value="False">
                        <Setter TargetName="Border" Property="TextBlock.Foreground" Value="Gray" />
                        <Setter TargetName="Border" Property="Background" Value="MistyRose" />
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>