Question

I’m trying to pass a TextBlock to a converter through binding

<DataTemplate>
    <Grid>
        <DockPanel LastChildFill="False" x:Name="dpInfo">
            <Image Source = "{Binding Data.Picture}" Height="42" HorizontalAlignment="Left" Stretch="Uniform" VerticalAlignment="Center" Width="32" Margin="16,0,0,0" DockPanel.Dock="Left"/>
            <TextBlock Text= "{Binding Data.Name}" x:Name="tbUserName" VerticalAlignment="Center" Padding="10,0,0,0" TextTrimming="CharacterEllipsis" DockPanel.Dock="Left"/>
            <TextBlock Text=  "{Binding Data.ScribbleCount, StringFormat=' ({0})', Mode=TwoWay}" VerticalAlignment="Center" DockPanel.Dock="Left"/>
        </DockPanel>
        <Rectangle x:Name="rctClickableArea" MouseLeftButtonDown="User_MouseLeftButtonDown" Fill="Black" Opacity="0">
            <Rectangle.ToolTip>
                <ToolTip DataContext="{Binding Path=PlacementTarget.DataContext, RelativeSource={x:Static RelativeSource.Self}}">
                    <ToolTip.Visibility>
                        <MultiBinding Converter="{StaticResource TooltipVisibilityConverter}">
                            <MultiBinding.Bindings>
                                <Binding Path="Data.Name"/>
                                <Binding ElementName="tbUserName"/>
                            </MultiBinding.Bindings>
                        </MultiBinding>
                    </ToolTip.Visibility>

                    <TextBlock Text="{Binding Data.Name}"/>

                </ToolTip>
            </Rectangle.ToolTip>
        </Rectangle>
    </Grid>
</DataTemplate>

The binding to the DataContext (Binding Path=”Data.Name”) works but the binding (Binding ElementName=”tbUserName”) does not work, where tbUserName is a TextBlock in the dbInfo DockPanel. Do you have any ideas on how to bind this correctly?

Answer 1

You might be having two issues…

NameScoping …

ElementName binding has stringent restrictions about NameScoping…

Basically, when an ElementName is used
in a binding, the NameScope of the target object is used to locate the
element with the specified name. If that element doesn’t have a
NameScope specifically on it, the FrameworkElement.FindScope method
continues up the logical tree and falls back to the inheritance
context if there is no logical parent. The name scope is the object in
which all named objects have been registered.

So in your case referring element outside the ToolTip’s context fails. Now for this to work correct you will have to bridge the broken scope using something like Tag property…

 <Rectangle Tag="{Binding ElementName tbUserName}" ...>
    <Rectangle.ToolTip>
       <ToolTip ...>
          <ToolTip.Visibility ... >
             <MultiBinding>
                 <Binding Path="Data.Name" />
                 <Binding Path="Tag"
                          RelativeSource="{RelativeSource
                             AncestorType={x:Type Rectangle}}" ...>

Visibility of ToolTip

Instead of binding to visibility of tooltip, you could use a data-trigger with multi binding on rectangle itself and set the tooltip that you want, based on the condition value…

    <Window.Resources>
       <local:TooltipVisibilityConverter x:Key="TooltipVisibilityConverter"/>
       <TextBlock x:Key="MyToolTip" Text="{Binding Data.Name}"/>
     </Window.Resources>

    <!-- Rest of the code --->

    <Rectangle.Style>
        <Style TargetType="{x:Type Rectangle}">
            <Style.Triggers>
                <DataTrigger Value="True">
                    <DataTrigger.Binding>
                          <MultiBinding
                                Converter="{StaticResource
                                   TooltipVisibilityConverter}">
                                <MultiBinding.Bindings>
                                    <Binding Path="Data.Name"/>
                                    <Binding ElementName="HelloTB"/>
                                </MultiBinding.Bindings>
                            </MultiBinding> 
                        </DataTrigger.Binding>
                        <Setter Property="ToolTip"
                                Value="{StaticResource MyToolTip}"/>
                    </DataTrigger>
                </Style.Triggers>
            </Style>
    </Rectangle.Style>

Notice that TooltipVisibilityConverter now returns a boolean for sake of simplicity.