FormStartPosition.CenterParent does not work

Question

In the following code, only the second method works for me (.NET 4.0). FormStartPosition.CenterParent does not center the child form over its parent. Why?

Answer 1

I realize this is an old question, but I was recently having the same problem and for reasons I won't get in to, I did not want to use the form.ShowDialog() method and my application was not an MDI application, therefore the CenterParent method was not having any effect. This is how I solved the problem, by computing the coordinates for the form that I wanted centered and triggering the new location in the main form's LocationChanged event. Hopefully this will help someone else having this problem.

In the example below, the parent form is called MainForm and the form I want centered in MainForm is called pleaseWaitForm.

private void MainForm_LocationChanged(object sender, EventArgs e)
    {
        Point mainFormCoords = this.Location;
        int mainFormWidth = this.Size.Width;
        int mainFormHeight = this.Size.Height;
        Point mainFormCenter = new Point();
        mainFormCenter.X = mainFormCoords.X + (mainFormWidth / 2);
        mainFormCenter.Y = mainFormCoords.Y + (mainFormHeight / 2);
        Point waitFormLocation = new Point();
        waitFormLocation.X = mainFormCenter.X - (pleaseWaitForm.Width / 2);
        waitFormLocation.Y = mainFormCenter.Y - (pleaseWaitForm.Height / 2);
        pleaseWaitForm.StartPosition = FormStartPosition.Manual;
        pleaseWaitForm.Location = waitFormLocation;           
    } 

If you have a resizable parent form and you wanted your sub form to also be centered whenever the main form is resized, you should, in theory, be able to place this code in a method and then call the method on both the LocationChanged and SizeChanged events.