Disposing WPF User Controls

Question

I have created a custom WPF user control which is intended to be used by a third party. My control has a private member which is disposable, and I would like to ensure that its dispose method will always get called once the containing window/application is closed. However, UserControl is not disposable.

I tried implementing the IDisposable interface and subscribing to the Unloaded event but neither get called when the host application closes. MSDN says that the Unloaded event may not be raised at all. And it might also be triggered more than once, that is when user changes theme.

If at all possible, I don't want to rely on consumers of my control remembering to call a specific Dispose method.

 public partial class MyWpfControl : UserControl
 {
     SomeDisposableObject x;

     // where does this code go?
     void Somewhere() 
     {
         if (x != null)
         {
             x.Dispose();
             x = null;
         }

     }
 }

The only solution I have found so far is to subscribe to the Dispatcher's ShutdownStarted event. Is this a reasonable approach?

this.Dispatcher.ShutdownStarted += Dispatcher_ShutdownStarted;

Ray_Booysen_42124 · Answer

Interesting blog post here: Dispose of a WPF UserControl (ish)

It mentions subscribing to Dispatcher.ShutdownStarted to dispose of your resources.

user_125523 · Answer

You have to be careful using the destructor. This will get called on the GC Finalizer thread. In some cases the resources that your freeing may not like being released on a different thread from the one they were created on.

user_91260 · Answer

I'm thinking unload is called all but at hard exist in 4.7. But, if you are playing around with older versions of .Net, try doing this in your loading method:

e.Handled = true;

I don't think older versions will unload until loading is handled. Just posting because I see others still asking this question, and haven't seen this proposed as a solution. I only touch .Net a few times a year, and ran into this a few years back. But, I wonder if it's as simple as unload not being called until loading has finished. Seems like it works for me, but again in newer .Net it seems to always call unload even if loading isn't marked as handled.

Admin · Answer

An UserControl has a Destructor, why don't you use that?

~MyWpfControl()
    {
        // Dispose of any Disposable items here
    }

Disposing WPF User Controls

7 Answers