Question

Somewhere on _VisibleChanged event I am changing the ActiveControl:

private void ResultNumeric_VisibleChanged(object sender, EventArgs e)
{
    if (this.Visible)
    {
        this.ActiveControl = this.resNumResult;
    }
}

Now if I follow one work flow of the program, my app is crashing. I looked at the StackTrace and it has a call to REMOVE in it which will set the Parent to null and actually crash is also coming from a place that I am calling a method on a a parent this is null.

   at System.Windows.Forms.ContainerControl.AfterControlRemoved(Control control, Control oldParent)
   at System.Windows.Forms.SplitContainer.AfterControlRemoved(Control control, Control oldParent)
   at System.Windows.Forms.Control.ControlCollection.Remove(Control value) 

So is it this change of ActiveControl that is causing the Remove method to be called?

Answer 1

I don’t think that setting the ActiveControl removes a control from form’s ControlCollection. The error must be somewhere else. Do you have a remove of a control somewhere else in your code?