How to modify Silverlight template at runtime?

Question

I have a custom control containing a path that has a templated tooltip. I want to be able to get a reference to a grid in the template at runtime so that I can modify it's children depending on use.

I thought I could use GetTemplateChild to get a reference to the grid in the template from within the OnApplyTemplate method of the control but this method is not firing.

public override void OnApplyTemplate()
{
  base.OnApplyTemplate();

  _tooltipDetails = (Grid)GetTemplateChild("TooltipDetailsGrid");
}

How else might I be able to do this?

Here is the user control's XAML.

<UserControl
    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" x:Class="MiX.AssetManagement.UI.Timeline.Silverlight.TimelineBarRibbonItem"
    FontSize="9.333" Foreground="White" mc:Ignorable="d">
    <UserControl.Resources>
        <ControlTemplate x:Key="ToolTipControlTemplateTimelineView" TargetType="ToolTip">
            <StackPanel Orientation="Horizontal" Margin="16,0,0,0">
                <VisualStateManager.VisualStateGroups>
                    <VisualStateGroup x:Name="OpenStates">
                        <VisualState x:Name="Closed"/>
                        <VisualState x:Name="Open"/>
                    </VisualStateGroup>
                </VisualStateManager.VisualStateGroups>
                <Border CornerRadius="4">
                    <Border.Background>
                        <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                            <GradientStop Color="#7F000000" Offset="0"/>
                            <GradientStop Color="#B2000000" Offset="1"/>
                        </LinearGradientBrush>
                    </Border.Background>
                    <Grid Margin="4">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition/>
                            <ColumnDefinition/>
                        </Grid.ColumnDefinitions>
                        <Border x:Name="Info" Height="16" Width="16" BorderThickness="2" CornerRadius="8" HorizontalAlignment="Left" VerticalAlignment="Top">
                            <Border.BorderBrush>
                                <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                                    <GradientStop Color="White" Offset="0"/>
                                    <GradientStop Color="#7FFFFFFF" Offset="1"/>
                                </LinearGradientBrush>
                            </Border.BorderBrush>
                            <Path Fill="White" Stretch="Fill" Margin="5.229,2.089,5.035,2.82" RenderTransformOrigin="0.5,0.5" UseLayoutRounding="False" Data="M0.77471197,5.0623446 L2.4198356,5.0623446 L2.4198356,10.18 L0.77471197,10.18 z M0.72914064,3.0891075 L2.4654069,3.0891075 L2.4654069,4.3332038 L0.72914064,4.3332038 z">
                                <Path.RenderTransform>
                                    <TransformGroup>
                                        <ScaleTransform/>
                                        <SkewTransform/>
                                        <RotateTransform/>
                                        <TranslateTransform/>
                                    </TransformGroup>
                                </Path.RenderTransform>
                            </Path>
                        </Border>
                        <ContentPresenter d:LayoutOverrides="Width, Height" Margin="20,0,0,0"/>
                        <Grid Grid.Column="1" x:Name="TooltipDetailsGrid">
                            <TextBlock Text="Tooltip in a Grid"/>
                        </Grid>
                    </Grid>
                </Border>
            </StackPanel>
        </ControlTemplate>
    </UserControl.Resources>

    <Path x:Name="RibbonItem" Cursor="Hand">
        <Path.Fill>
            <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                <GradientStop Color="#FF66CC33"/>
                <GradientStop Color="#FF339900" Offset="1"/>
            </LinearGradientBrush>
        </Path.Fill>
        <ToolTipService.ToolTip>
            <ToolTip x:Name="RibbonItemTooltip" Content="" Foreground="#FFFFFFFF" FontSize="9.333" Placement="Mouse" Template="{StaticResource ToolTipControlTemplateTimelineView}"/>
        </ToolTipService.ToolTip>
        <Path.Data>
            <GeometryGroup x:Name="RibbonItemGeometryGroup">
                <RectangleGeometry x:Name="RibbonItemBackground" />
            </GeometryGroup>
        </Path.Data>
    </Path>
</UserControl>

Answer 1

I have resolved this in a slightly different way. Rather than modify the template at runtime I have created an instance of the template for each use case. I can then apply the correct template when I create the instance and elements in the template bind to control class to populate the tooltip with the appropriate values.

This is probably a better approach as the structure of the tooltips is now clearly visible in the XAML, rather than being hidden away in the code.

Answer 2

You need to be handling code in the ToolTip Classes OnApplyTemplate method. Here is my untested stab at what you need to do:-

Inherit from ToolTip and override the OnApplyTemplate method in this new class:-

 public MyToolTip : ToolTip
 {
     public override void OnApplyTemplate()
     {
         //Perhaps to stuff
         base.OnApplyTemplate();
         //Perhaps to other stuff
     }
 }

In your resources you now set the TargetType to local:MyToolTip and ensure your assembly namespace is placed with the local alias in the user control element.

Now in your Xaml:-

    <ToolTipService.ToolTip>
            <local:MyToolTip x:Name="RibbonItemTooltip" Content="" Foreground="#FFFFFFFF" FontSize="9.333" Placement="Mouse" Template="{StaticResource ToolTipControlTemplateTimelineView}"/>
    </ToolTipService.ToolTip>