Silverlight does not come with an Unloaded event like it’s big brother WPF. Here is a very simple behavior that adds support for it.
A Blend user simply has to supply the target method name and the target method context (Control or DataContext) and the method will be executed when the control has been removed from the visual tree.
using System;
using System.Reflection;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Interactivity;
using System.Windows.Media;
namespace SilverlighUnloadedBehavior
{ public enum TargetMethodExecuteMode
{ DataContext,
AssociatedObject
}
public class UnloadedBehavior : Behavior<Control>
{ #region MethodExecuteMode
public static readonly DependencyProperty MethodExecuteModeProperty =
DependencyProperty.Register("MethodExecuteMode", typeof(TargetMethodExecuteMode), typeof(UnloadedBehavior), new PropertyMetadata(TargetMethodExecuteMode.AssociatedObject, OnMethodExecuteModeChanged));
public TargetMethodExecuteMode MethodExecuteMode
{ get { return (TargetMethodExecuteMode)GetValue(MethodExecuteModeProperty); } set { SetValue(MethodExecuteModeProperty, value); } }
private static void OnMethodExecuteModeChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{ ((UnloadedBehavior)d).OnMethodExecuteModeChanged(e);
}
protected virtual void OnMethodExecuteModeChanged(DependencyPropertyChangedEventArgs e)
{ }
#endregion
#region TargetMethod
public static readonly DependencyProperty TargetMethodProperty =
DependencyProperty.Register("TargetMethod", typeof(string), typeof(UnloadedBehavior), new PropertyMetadata("", OnTargetMethodChanged));
public string TargetMethod
{ get { return (string)GetValue(TargetMethodProperty); } set { SetValue(TargetMethodProperty, value); } }
private static void OnTargetMethodChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{ ((UnloadedBehavior)d).OnTargetMethodChanged(e);
}
protected virtual void OnTargetMethodChanged(DependencyPropertyChangedEventArgs e)
{ }
#endregion
protected override void OnAttached()
{ base.OnAttached();
AssociatedObject.LayoutUpdated += AssociatedObject_LayoutUpdated;
}
private void AssociatedObject_LayoutUpdated(object sender, EventArgs e)
{ if (!InTree())
ExecuteTargetMethod();
}
protected bool InTree()
{ FrameworkElement element = AssociatedObject;
var rootElement = Application.Current.RootVisual as FrameworkElement;
while (element != null)
{ if (element == rootElement)
return true;
element = VisualTreeHelper.GetParent(element) as FrameworkElement;
}
return false;
}
private void ExecuteTargetMethod()
{ if(string.IsNullOrEmpty(TargetMethod))
return;
Type contextType;
object targetMethodObject;
switch(MethodExecuteMode)
{ case TargetMethodExecuteMode.DataContext:
targetMethodObject = AssociatedObject.DataContext;
if (targetMethodObject == null)
return;
contextType = AssociatedObject.DataContext.GetType();
break;
case TargetMethodExecuteMode.AssociatedObject:
targetMethodObject = AssociatedObject;
contextType = AssociatedObject.GetType();
break;
default:
throw new ArgumentOutOfRangeException();
}
if(targetMethodObject == null)
return;
MethodInfo method = contextType.GetMethod(TargetMethod);
if (method == null)
return;
method.Invoke(targetMethodObject, null);
}
protected override void OnDetaching()
{ AssociatedObject.LayoutUpdated -= AssociatedObject_LayoutUpdated;
base.OnDetaching();
}
}
}