Show a child form in the centre of Parent form in C#

Question

I create a new form and call from the parent form as follows:

loginForm = new SubLogin();   
loginForm.Show();

I need to display the child form at the centre of the parent. So,in the child form load I do the foll:`

Point p = new Point(this.ParentForm.Width / 2 - this.Width / 2, this.ParentForm.Height / 2 - this.Height / 2);
this.Location = p;

But this is throwing error as parent form is null. I tried setting the Parent property as well, but didn't help. Any inputs on this?

Answer 1

Try:

loginForm.StartPosition = FormStartPosition.CenterParent;
loginForm.ShowDialog(this);

Of course the child for will now be a blocking form (dialog) of the parent window, if that isn't desired then just replace ShowDialog with Show..

loginForm.Show(this);

You will still need to specify the StartPosition though.

Answer 2

On the SubLogin Form I would expose a SetLocation method so that you can set it from your parent form:

public class SubLogin : Form
{
   public void SetLocation(Point p)
   {
      this.Location = p;
   }
}

Then, from your main form:

loginForm = new SubLogin();   
Point p = //do math to get point
loginForm.SetLocation(p);
loginForm.Show();

Answer 3

Assuming your code is running inside your parent form, then something like this is probably what you're looking for:

loginForm = new SubLogin();
loginForm.StartPosition = FormStartPosition.CenterParent
loginForm.Show(this);

For the record, there's also a Form.CenterToParent() function, if you need to center it after creation for whatever reason too.

Answer 4

The parent probably isn't yet set when you are trying to access it.

Try this:

loginForm = new SubLogin();
loginForm.Show(this);
loginForm.CenterToParent()

Answer 5

You need this:

Replace Me with this.parent, but you need to set parent before you show that form.

  Private Sub ÜberToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ÜberToolStripMenuItem.Click

        'About.StartPosition = FormStartPosition.Manual ' !!!!!
        About.Location = New Point(Me.Location.X + Me.Width / 2 - About.Width / 2, Me.Location.Y + Me.Height / 2 - About.Height / 2)
        About.Show()
    End Sub