I have defined the following DataTemplate
for ListBox
items in an external resource dictionary:
<DataTemplate x:Key="MyListBoxItemTemplate" DataType="{x:Type entities:Track}">
<StackPanel>
<TextBlock Text="Here's the slider:" />
<Slider Name="MySlider" Height="23" Minimum="0" />
</StackPanel>
</DataTemplate>
I need to provide an event handler method for Slider's ValueChanged
event. I don't know where am I supposed to write that code as it is impractical to specify event handler for a control within a template.
I've been googling for the solution and found that I should add the event handler in the override of the OnApplyTemplate()
method. My guess is that it should look something like this or similar:
public override void OnApplyTemplate()
{
base.OnApplyTemplate();
// Is the following initialization even going to work!?!?
Slider MySlider = this.FindName("MySlider") as Slider;
SeekSlider.ValueChanged +=
new RoutedPropertyChangedEventHandler<double>(SeekSlider_ValueChanged);
}
But where should I write this method? Does OnApplyTemplate overriding only applies to ControlTemplates or is my scenario included as well? Should I provide ControlTemplate instead of DataTemplate? Is the body of the method I have provided correct?
Please help. Thanks.
Using the OnApplyTemplate
approach will work if you if you're working with the ControlTemplate
for a Control. For example, if you've subclassed TextBox
you could do this like
public class MyTextBox : TextBox
{
public override void OnApplyTemplate()
{
MySlider MySlider = GetTemplateChild("MySlider") as MySlider;
if (MySlider != null)
{
MySlider.ValueChanged += new RoutedPropertyChangedEventHandler<double>(MySlider_ValueChanged);
}
base.OnApplyTemplate();
}
void MySlider_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
{
//...
}
}
I don't think this approach will work in your situation however. You could use the Loaded event for ListBoxItem
and find the Slider
in the visual tree in the event handler
<ListBox ...>
<ListBox.ItemContainerStyle>
<Style TargetType="ListBoxItem">
<EventSetter Event="Loaded" Handler="ListBoxItem_Loaded"/>
</Style>
</ListBox.ItemContainerStyle>
<!--...-->
</ListBox>
Code behind
private void ListBoxItem_Loaded(object sender, RoutedEventArgs e)
{
ListBoxItem listBoxItem = sender as ListBoxItem;
Slider MySlider = GetVisualChild<Slider>(listBoxItem);
MySlider.ValueChanged += new RoutedPropertyChangedEventHandler<double>(MySlider_ValueChanged);
}
void MySlider_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
{
}
GetVisualChild
private static T GetVisualChild<T>(DependencyObject parent) where T : Visual
{
T child = default(T);
int numVisuals = VisualTreeHelper.GetChildrenCount(parent);
for (int i = 0; i < numVisuals; i++)
{
Visual v = (Visual)VisualTreeHelper.GetChild(parent, i);
child = v as T;
if (child == null)
{
child = GetVisualChild<T>(v);
}
if (child != null)
{
break;
}
}
return child;
}