Safe event detachment base class for Windows Phone 7 behaviors - Init

<body> <h1>Safe event detachment base class for Windows Phone 7 behaviors</h1> <p><a href="http://feedads.g.doubleclick.net/~a/sXNaucEX5U2DS_Q1QNrc1mPeIwc/0/da"><img src="http://feedads.g.doubleclick.net/~a/sXNaucEX5U2DS_Q1QNrc1mPeIwc/0/di" border="0" ismap="true"></img></a><br/> <a href="http://feedads.g.doubleclick.net/~a/sXNaucEX5U2DS_Q1QNrc1mPeIwc/1/da"><img src="http://feedads.g.doubleclick.net/~a/sXNaucEX5U2DS_Q1QNrc1mPeIwc/1/di" border="0" ismap="true"></img></a></p><p>Some time ago I blogged about the <a href="http://dotnetbyexample.blogspot.com/2011/04/safe-event-detachment-pattern-for.html" target="_blank">Safe Event Detachment ‘pattern’ for behaviors</a> and even included a snippet that made implementing this pattern easier. When I started to use this pattern more often myself I observed quite some code duplication appearing and I don’t like that. What’s more – although the pattern works well under Silverlight and WPF, there are some unique situations in <a href="http://www.microsoft.com/windowsphone/" target="_blank">Windows Phone 7</a> that need some extra attention – particularly the situation in which the user is navigating <em>back</em> to a page containing such a behavior. For when the user is navigation <em>from</em> the page, the AssociatedObject’s <em>Unloaded</em> event fires and the behavior is de-activated. If the user then moves back to the page – the AssociatedObject’s <em>OnAttached</em> event is <em>not</em> fired and the behavior is not re-initialized. </p>So I set out to create a base class taking care of most of this initalization hooplah without bothering the developer too much. This turned out to be not so simple as I thought. But anyway – thinks worked out. The initial setup of the base class is like this:<pre style="font-size: 12px">using System; using System.Windows; using System.Windows.Interactivity; using System.Windows.Navigation; using Microsoft.Phone.Controls; namespace Wp7nl.Behaviors { /// <summary> /// A base class implementing the safe event detachment pattern for behaviors. /// Optional re-init after page back navigation. /// </summary> /// <typeparam name="T">The framework element type this behavior attaches to</typeparam> public abstract class SafeBehavior<T> : Behavior<T> where T : FrameworkElement { protected SafeBehavior() { IsCleanedUp = true; } /// <summary> ///Setting this value to true in the constructor makes the behavior ///re-init after a page back event. /// </summary> protected bool ListenToPageBackEvent { get; set; } /// <summary> /// The page this behavior is on /// </summary> protected PhoneApplicationFrame ParentPage; /// <summary> /// The uri of the page this behavior is on /// </summary> private Uri pageSource; protected override void OnAttached() { base.OnAttached(); InitBehavior(); } /// <summary> /// Does the initial wiring of events /// </summary> protected void InitBehavior() { if (IsCleanedUp) { IsCleanedUp = false; AssociatedObject.Loaded += AssociatedObjectLoaded; AssociatedObject.Unloaded += AssociatedObjectUnloaded; } } } }</pre> <p>The comments already give away which direction this is going to take: the behavior keeps track of the page it’s on <em>and that page’s u</em><em>ri</em> to track if the user is navigating back to this page. If you don’t want this behavior, do nothing. If you <em>need</em> to track the user navigating back to the page (and believe me, in Windows Phone 7 you want that in most of the cases), set ListenToPageBackEvent to true in the behavior’s constructor. The setting up of this tracking is done in the next method:</p><pre style="font-size: 12px">/// <summary> /// Does further event wiring and initialization after load /// </summary> /// <param name="sender"></param> /// <param name="e"></param> private void </body>