Error creating window handle.

I have been chasing a bug in a VB.NET Windows Forms application today. The error log was filled with Win32Exception Error creating window handle. Digging in the usage log I loacted the following code.

   1: Public Sub DataBindRadioButton(ByVal radioButton As Windows.Forms.RadioButton, ByVal radioButtonTrueValue As Object, ByVal radioButtonFalseValue As Object, ByRef dataSource As Object, ByVal dataMember As String)

   2:      Dim propertyHolder As New propertyHolder(radioButton, radioButtonTrueValue, radioButtonFalseValue, dataSource, dataMember)

   3:      propertyHolder.Name = radioButton.Name & "propertyHolder"

   4:  

   5:      For Each control As control In radioButton.FindForm.Controls

   6:          If control.Name = propertyHolder.Name Then

   7:              radioButton.FindForm.Controls.Remove(control)

   8:              Exit For

   9:          End If

  10:      Next

  11:  

  12:      radioButton.FindForm.Controls.Add(propertyHolder)

  13:  End Sub

propertyHolder is a Control.

So whats the memory leak here?

radioButton.FindForm.Controls.Remove(control), since we remove the control from the container(Form). We now inherit the responsibility to clean up.

So a non leaking version would be.

   1: Public Sub DataBindRadioButton(ByVal radioButton As Windows.Forms.RadioButton, ByVal radioButtonTrueValue As Object, ByVal radioButtonFalseValue As Object, ByRef dataSource As Object, ByVal dataMember As String)

   2:       Dim propertyHolder As New propertyHolder(radioButton, radioButtonTrueValue, radioButtonFalseValue, dataSource, dataMember)

   3:       propertyHolder.Name = radioButton.Name & "propertyHolder"

   4:  

   5:       For Each control As control In radioButton.FindForm.Controls

   6:           If control.Name = propertyHolder.Name Then

   7:               radioButton.FindForm.Controls.Remove(control)

   8:       control.Dispose()

   9:               Exit For

  10:           End If

  11:       Next

  12:  

  13:       radioButton.FindForm.Controls.Add(propertyHolder)

  14:   End Sub

So remember to dispose a control when you dynamically remove it from its container.

The application also had a while loop that in some conditions never exited, and called the above method.