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+1 A:

We just experienced the same thing at work. This doesn't appear to be a bug in the WPFToolkit, rather there is an issue with Expression Blend which crops up because the people who made the original template got a little tricky.

First, go grab the default template. If you download the source they will be in Toolkit-Release/Calendar/Themes/Generic.xaml. The source can be found on the WPF Toolkit CodePlex site. http://wpf.codeplex.com/

The CalendarItemTemplate has this sort of a setup:

<Style TargetType="primitives:CalendarItem">
...
<Setter Property="Template">
   <Setter.Value>
      <ControlTemplate TargetType="primitives:CalendarItem">
          ...
          <Grid Name="PART_Root" >
              <Border 
                  ...  
                   <Border CornerRadius="1" BorderBrush="#FFFFFFFF" BorderThickness="2">
                       <Grid>
                           <Grid.Resources>
                               <ControlTemplate x:Key="HeaderButtonTemplate" TargetType="Button">
                           ...
                            <Button x:Name="PART_HeaderButton" Template="{StaticResource HeaderButtonTemplate}"    
                           ...

This is the original HeaderButtonTemplate:

<ControlTemplate x:Key="HeaderButtonTemplate" TargetType="Button">
    <Grid Cursor="Hand">
        <vsm:VisualStateManager.VisualStateGroups>
            <vsm:VisualStateGroup x:Name="CommonStates">
                <vsm:VisualState x:Name="Normal" />
                <vsm:VisualState x:Name="MouseOver">
                    <Storyboard>
                        <ColorAnimation Storyboard.TargetName="TextColor" Storyboard.TargetProperty="Color" To="#FF73A9D8" Duration="0" />
                    </Storyboard>
                </vsm:VisualState>
                <vsm:VisualState x:Name="Disabled">
                    <Storyboard>
                        <DoubleAnimation Storyboard.TargetName="buttonContent" Storyboard.TargetProperty="Opacity" To=".5" Duration="0" />
                    </Storyboard>
                </vsm:VisualState>
            </vsm:VisualStateGroup>
        </vsm:VisualStateManager.VisualStateGroups>
        <ContentPresenter
          x:Name="buttonContent"
          Content="{TemplateBinding Content}"
          ContentTemplate="{TemplateBinding ContentTemplate}"
          Margin="1,4,1,9"
          HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
          VerticalAlignment="{TemplateBinding VerticalContentAlignment}">
             <TextElement.Foreground>
                <SolidColorBrush x:Name="TextColor" Color="#FF333333"/>
            </TextElement.Foreground>
        </ContentPresenter>
    </Grid>
</ControlTemplate>

The part that concerns us is here:

<ContentPresenter
  x:Name="buttonContent"
  Content="{TemplateBinding Content}"
  ContentTemplate="{TemplateBinding ContentTemplate}"
  Margin="1,4,1,9"
  HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
  VerticalAlignment="{TemplateBinding VerticalContentAlignment}">
     <TextElement.Foreground>
        <SolidColorBrush x:Name="TextColor" Color="#FF333333"/>
    </TextElement.Foreground>
</ContentPresenter>

Notice the TextElement attached property setter that instantiates the SolidColorBrush. This is the named brush that is targeted by the storyboards.

When you do the "Edit Copy of Template" thing in Blend, it will inline some of the templates so that the Header button template will be set directly instead of being contained in the grid resources.

<Button x:Name="PART_HeaderButton" HorizontalAlignment="Center" VerticalAlignment="Center" FontSize="10.5" FontWeight="Bold" Focusable="False" Grid.Column="1" Grid.Row="0">
 <Button.Template>
  <ControlTemplate TargetType="{x:Type Button}">
   <Grid Cursor="Hand">

I don't know why it does this, when I edit a copy of a template I'm expecting an actual copy of the template. I suppose I understand that sometimes a template is referenced from outside, but in this case it's not - and even if it is it seems more prudent to copy it in its entirety and add it to the style/controltemplate resources. What is worse, as part of the reprocessing Blend modifies the contentpresenter definition in the template, turning it into this:

<ContentPresenter x:Name="buttonContent" 
    HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" 
    Margin="1,4,1,9" 
    VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
    ContentTemplate="{TemplateBinding ContentTemplate}"
    Content="{TemplateBinding Content}"
    TextElement.Foreground="#FF333333"  />

So, in other words no more named brush, and the storyboard target is now incorrect.

Fortunately the fix is easy - use the original template as your starting point. Trouble is, blend doesn't like it and won't display because for some reason it can only set this attached property on the contentpresenter as part of the opening tag, not in the expanded mode or whatever it's called. Of course, it's probably quite possible to duplicate the functionality in another manner that is more blendable.

EDIT: Here is a quick way to hack up the template to make it blendable. And it really is a hack, though mostly a harmless one. I don't advocate doing things like this normally, but it does seem to work fine.

<ControlTemplate x:Key="HeaderButtonTemplate" TargetType="Button">
    <Grid Cursor="Hand">
     <vsm:VisualStateManager.VisualStateGroups>
      <vsm:VisualStateGroup x:Name="CommonStates">
       <vsm:VisualState x:Name="Normal" />
       <vsm:VisualState x:Name="MouseOver">
        <Storyboard>
         <ColorAnimation Storyboard.TargetName="TextColor" Storyboard.TargetProperty="Color" To="#FF73A9D8" Duration="0" />
        </Storyboard>
       </vsm:VisualState>
       <vsm:VisualState x:Name="Disabled">
        <Storyboard>
         <DoubleAnimation Storyboard.TargetName="buttonContent" Storyboard.TargetProperty="Opacity" To=".5" Duration="0" />
        </Storyboard>
       </vsm:VisualState>
      </vsm:VisualStateGroup>
     </vsm:VisualStateManager.VisualStateGroups>
     <!-- A dummy Rectangle that is essentially a container for the TextColor brush -->
     <Rectangle Width="0" Height="0">
      <Rectangle.Fill>
       <SolidColorBrush x:Name="TextColor" Color="#FF333333"/>
      </Rectangle.Fill> 
     </Rectangle>
     <ContentPresenter
                x:Name="buttonContent"
                Content="{TemplateBinding Content}"
                ContentTemplate="{TemplateBinding ContentTemplate}"
                Margin="1,4,1,9"
                HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                TextElement.Foreground="{Binding ElementName=TextColor}">
     </ContentPresenter>
    </Grid>
</ControlTemplate>

The essense of it is to house the brush as part of another object - technically visible if too small to be shown, and then do a binding on the contentpresenter - because it's done in the opening tag Blend doesn't complain. Yeah I know, this sort of smells, but it's the smallest rewrite of the original template that I can see to make it work.

Egor 2009-10-02 04:57:11

Accepted *and* an upvote. Thanks for the answer to a particularly thorny question!

David Veeneman 2009-10-02 13:02:49

Submitted as a bug on the Expression Blend Feedback page: https://connect.microsoft.com/Expression/feedback/ViewFeedback.aspx?FeedbackID=495224

David Veeneman 2009-10-02 15:09:29

You welcome - I edited my answer to provide a quick and sort of dirty way to make it blendable.

Egor 2009-10-02 20:05:53

David Veeneman 2009-10-03 11:25:53

Interesting - the template rewrite I can understand, I've never browsed xaml resources with Reflector+BamlViewer though I should. Without doing so I can't say what Blend has access to. But it seems that at the very least Blend should not freak out about assigning a textelement.foreground to a content presenter - especially when it works fine at runtime, in cider, and doesn't seem to break the rules.

Egor 2009-10-05 08:01:33

VisualStateManager.VisualStateGroups is just like hell. It doesn't let me compile the app with that custom style for calendar. It throws an exception on editor: The attachable property 'VisualStateGroups' was not found in type 'VisualStateManager'

Junior Mayhé 2009-10-27 16:34:36

That's strange, it compiled and ran just fine for me. The error also doesn't seem to make sense - are you sure that everything is referenced correctly?

Egor 2009-10-27 21:05:18

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