How to modify Silverlight template at runtime? - silverlight

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

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>

Answer 2

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.