Question

I have create a lookless control to be used in a Silverlight 4 project. This control contains a button and I would like to capture the click event. The Generic.xaml contains

<Style TargetType="TU:MyControl">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="TU:MyControl" >
                <Border Background="{TemplateBinding Background}"
                        BorderBrush="{TemplateBinding BorderBrush}"
                        BorderThickness="{TemplateBinding BorderThickness}" d:DesignWidth="550" d:DesignHeight="228">
                    <Grid Background="Silver">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="150*"/>
                            <ColumnDefinition Width="60"/>
                            <ColumnDefinition Width="150*"/>
                        </Grid.ColumnDefinitions>
                        <Border Grid.Column="0" Margin="2" BorderBrush="DarkGray" BorderThickness="3"></Border>
                        <Border Grid.Column="2" Margin="2" BorderBrush="DarkGray" BorderThickness="3"></Border>
                        <StackPanel Grid.Column="1">
                            <Button Name="PART_MyClick"  Height="32" Width="32" Margin="0,8,0,0"></Button>
                        </StackPanel>
                    </Grid>
                </Border>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

After researching the problem I beleive that I have to add the following attribute to my control class

[TemplatePart(Name = "PART_MyClick", Type = typeof(Button))]

Then in my controls constructor I have added the following code

var myClick = GetTemplateChild("PART_MyClick") as Button;
if(myClick != null)
{
    myClick.Click += (o, e) => DoThings();
}

when run though the myClick variable is always null so the event handler never gets attached. Could you please tell me where I am going wrong? Im a newbie so if this is the wrong approach completly then any advise on the correct approach would also be greatfully received

Answer 1

Override the OnApplyTemplate method and put your code there instead of the control’s constructor:

public override void OnApplyTemplate()
{
    base.OnApplyTemplate();
    var myClick = GetTemplateChild("PART_MyClick") as Button;
    if(myClick != null)
    {
        myClick.Click += (o, e) => DoThings();
    }
}

Because during the constructor call the visual tree for the control is not build up yet. From MSDN OnApplyTemplate:

Attach class-defined event handlers to parts of the template. For
example, you might want class logic to handle KeyDown events from a
TextBox template part so that UI states are updated, and other events
that are specific to your control are raised instead.