Question

I have a window that have a user control. This user control has a button which maximize the user control to full screen.

For achieving this I have created a temporary window which I scale to current screen bounds and set it content to the user control.

private void OnBtnMaximizeClick(object sender, RoutedEventArgs e)
    {
      if (this.btnMaximize.IsChecked == true)
      {
        if (tempfullScreenWindow == null)
        {
          tempfullScreenWindow = new Window();
          tempfullScreenWindow.WindowStyle = WindowStyle.None;
          tempfullScreenWindow.ResizeMode = ResizeMode.NoResize;
        }
        var ownerWindow = Window.GetWindow(this);

        Screen screen = this.GetContainingScreen(ownerWindow);

        tempfullScreenWindow.Left = screen.WorkingArea.Left;
        tempfullScreenWindow.Top = screen.WorkingArea.Top;
        tempfullScreenWindow.Width = screen.Bounds.Width;
        tempfullScreenWindow.Height = screen.Bounds.Height;

        // InvalidOperationException comes here (Specified element is already the logical child of another element. Disconnect it first.)
        tempfullScreenWindow.Content = this;  

        tempfullScreenWindow.Owner = ownerWindow;
        tempfullScreenWindow.ShowDialog();
      }
      else
      {
        if (tempfullScreenWindow != null)
        {
          tempfullScreenWindow.Close();
        }
      }
    }

How can I set the usercontrol as content of the newly created window, by detaching it from owner window and when temp window is closed, re-attach the same to parent window.

Answer 1

Use

mywindow.Content = new MyuserControl();

Make sure for a control can have only one parent at a time. Detach from first window first and then attach it to other.