NullReferenceException when Disposing UserControl in Tab

Question

I am using C# WinForms.

I am using a usercontrol called AGauge. http://www.codearteng.com/2012/08/agauge-winforms-gauge-control.html I added the control to one of the tab pages in the Design view.

If I close the window without opening the tab page that contains the control, then I get a NullReferenceException (NullReferenceException occurred in AGauge.dll -- Object reference not set to an instance of an object)

If I open the tab page and then close the window, then everything works fine.

The exception happens in the Dispose() function when executing base.Dispose(disposing)

Since I don't have any view into the code in AGauge.dll, I am unsure what to do. I suppose I can create the controls at run-time when the tab page is opened, but that is not ideal.

Answer 1

I fixed the issue by creating the user control in the Selected() function of the tab control.

private void tb_Panel_Selected(object sender, TabControlEventArgs e)
{
    if (myUserControl == null)
    {
        this.myUserControl = new System.Windows.Forms.AGauge();
        ...
        ...
        this.Panel.Controls.Add(this.myUserControl)
    }
}