How do I add Dispose functionality to a C# UserControl?

Question

I have a class which implements UserControl. In .NET 2005, a Dispose method is automatically created in the MyClass.Designer.cs partial class file that looks like this:

  protected override void Dispose(bool disposing)
  {
     if (disposing && (components != null))
     {
        components.Dispose();
     }
     base.Dispose(disposing);
  }

If I want to add my own Dispose functionality, where would I put it? Since this file is generated, I don't want to add code here and risk it getting blown away.

Frenzy

Answer 1

In such a case I move the generated Dispose method to the main file and extend it. Visual Studio respects this.

An other approach would be using a partial method (C# 3.0).

Shillyshally

The Dispose method in Designer file could be extended to include a call to a partial method, which may be implemented in the main file. – Shillyshally

Since the MyClass.Designer.cs file is already a partial file, you can simply add the needed logic to the Dispose method already generated. Visual Studio will not overwrite the method once it's been created so you're safe to modify it. – Ecclesiolatry

Answer 2

All Component classes implement a Disposed event. You can add an event handler for that event and clean up things in there.

For example, in your UserControl you could add following method:

private void OnDispose(object sender, EventArgs e)
{
    // do stuff on dispose
}

And in constructor (or in Load event handler) add the following line:

Disposed += OnDispose;

Cavalry

@Jacob Seleznev: Not sure why more people didn't upvote this. Maybe they didn't see it? I consider the Disposed event the proper way to add disposal functionality to any class that supports it. – Jat

+1 - I agree with supercat that this is better than the current accepted answer. – Broadwater

I believe, that events are supposed to be handled from outside the class, not from the inside. I guess, that anyone may overwrite the event handler with his own and prevent the resources from being freed. The proper way to handle internal matters of a control is to override a proper virtual method provided by base class. – Shatterproof

If you need to perform logic on the components of the control, such as a BindingSource, using the Disposed event won't do the trick - the components have already been disposed by then. Taking control of the Dispose method appears to be the only way to completely control the flow here. In my case this was necessary to call BindingSource.Clear() to force the internally generated BindingList to detach PropertyChanged event handlers and prevent a memory leak. – Unclasp

Because the information conveyed by the disposing parameter in void Dispose(bool disposing) cannot be accessed through the Disposed event (or at least I cannot find it; the documentation for the Control.Disposing member does not indicate that it shares the semantics of the disposing parameter). Thus, only unmanaged resources can safely be disposed of with the Disposed event. – Wheeler

Answer 3

I believe in this case the code-generator honors your code. It should be safe to put it in the codebehind.

Grazing

Yes, it's not in the "genereted code" section of the file. – Poleyn

Answer 4

In VS 2005 (and 2008) you can update the Dispose method and it will not get removed when you edit the control from the designer.

Church

Answer 5

You can move it out from the .designer.cs file and into the main .cs file if you want. As has been said already, it won't be overwritten.

Gynarchy

Answer 6

You just need to overload the public void Dispose() method in the Component Class that the user control inherits.

make sure you pass the call to the base method as well as doing your dispose functionally or you'll break the functionality unless you fully implement it

Gerda

This is a great idea. For every Microsoft-implemented subclass of System.Windows.Forms.Control that you need more control over Dispose(bool disposing), you can subclass it and override Dispose there, adding a call to some virtual DisposeCore method like described in another question’s answer. You can read the value of the disposing parameter and still avoid editing the designer files. Win/win. – Wheeler

Answer 7

I would think the cleanest way would be to have your control subscribe to its own Disposed() event and do your cleanup in there.

Ruffianism

Answer 8

there is a Unloaded event for the UserControl that you can use to clean up,

Ayres

This question is about a WinForms UserControl, which does not have an Unloaded event. Perhaps you mean a WPF or Silverlight control? – Somewhat