Controls and IDisposable

After looking at how the Windows Forms designer handles components, I think it might be useful to have a quick look at how Controls are handled with regards to IDisposable.

Every Windows Forms control derives from the System.Windows.Forms.Control base class, which exposes the Controls property:

Public ReadOnly Property Controls() As ControlCollection

The implementation of the Control.Dispose(Boolean) is overridden in such a way that it iterates through the Controls collection calling the Dispose method for each member of the collection. The Windows Forms Designer "knows" this and the code it generates for Control-derived classes always adds controls to the Control.Controls collection that the Form class inherits from the Control class:

#Region " Windows Form Designer generated code "
...
<System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
Me.TextBox1 = New System.Windows.Forms.TextBox
...
Me.Controls.Add(Me.TextBox1)
End Sub
...
#End Region

This way, when the Form is being disposed, the contained controls are disposed automatically as well.

I don't really know why the Component containment support is not built into the Form class just like the Control containment represented by the Form.Controls collection. It would have been more consistent and also it would make the generated code smaller and more elegant. For example, it wouldn't have been necessary to neither generate the components member declaration, nor the Dispose(Boolean) method override. If someone is able to explain the reasoning behind this inconsistency, please let me know - I'm really curious about that.

If you've been designing a component that allocates UNMANAGED resources, please double check that you:

1. Implement the specific Public New(IContainer) constructor and add your component instance to the container by calling the IContainer.Add(Me) method in the constructor. (If you create your component using the Visual Studio .NET 'Component Class' template, it generates the specific constructor for you properly.)
2. Implement the IDisposable design pattern properly meaning that you do release the unmanaged resources and also that you do that exactly once.

Take a look here if you'd like to see an alternate IDisposable design pattern - more robust and elegant than its .NET counterpart, IMHO.