在C#中使用线程时，窗体不会在父窗体的中心打开

delegate void SetFormPositionDelegate(Form form);

private void OpenChildForm()
{
    ChildForm childForm = new ChildForm();
    childForm.StartPosition = FormStartPosition.CenterScreen;

    if (this.InvokeRequired)
    {
        this.Invoke(new SetFormPositionDelegate(SetFormPosition), childForm);
    }
    else
    {
        SetFormPosition(childForm);
    }

    childForm.Show();
}

private void SetFormPosition(Form form)
{
    form.StartPosition = FormStartPosition.CenterScreen;
}