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

Small Change to JYelton's answer

Form2_Load(object sender, EventArgs e)
{
    if (Owner != null && Parent == null && StartPosition == FormStartPosition.CenterParent)
    Location = new Point(Owner.Location.X + Owner.Width / 2 - Width / 2,
        Owner.Location.Y + Owner.Height / 2 - Height / 2);
}

Answer 2

If you set the owner of the child form like so:

Form2 f = new Form2();
f.Show(this);

You can then center it easily like this:

Form2_Load(object sender, EventArgs e)
{
    if (Owner != null)
        Location = new Point(Owner.Location.X + Owner.Width / 2 - Width / 2,
            Owner.Location.Y + Owner.Height / 2 - Height / 2);
}

Answer 3

I found a solution that will center modeless window position to parent's position, and the child window can be still covered by parent window. You just have to call

f2.Show(f1);

which will set f2 owner to f1, f2 will show over the f1 at it's center position.

Next you set

f2.Owner = null;

and there you go, f2 is a separate window, with correct startup position.

Answer 4

JYelton's answer worked for me, but the form is only centered the first time Show() is called. If you want to Hide() the form, and then have it re-centered on the parent every time Show() is called you need use the following in your form:

public new void Show(IWin32Window owner)
{
    base.Show(owner);

    if (Owner != null)
        Location = new Point(Owner.Location.X + Owner.Width / 2 - Width / 2,
            Owner.Location.Y + Owner.Height / 2 - Height / 2);
}

Answer 5

I found setting the location manually is the only reliable option in some more complex cases when form is auto-sized and dynamically modified.

However rather than computing the coordinates manually, I'd suggest using existing method:

this.CenterToParent();

Answer 6

An old question, I know, but I had the same issue but for a different reason.

The Form I was opening had an overridden OnLoad method:

protected override void OnLoad(EventArgs e)
{
   //... etc.
}

but was not calling the base implementation as it must do:

protected override void OnLoad(EventArgs e)
{
   //... etc.
   base.OnLoad(e);
}

When overriding OnLoad(EventArgs) in a derived class, be sure to call the base class's OnLoad(EventArgs) method so that registered delegates receive the event.