C# :: WPF / How To Check If Page Content Is Completely Rendered

In my program I have to load a page in a second window based on user's decision. This is how I do it:

case 1:
Page1 p1 = new Page1();
secondwindow.frame.Source = new Uri("p1.xaml", UriKind.Relative);
secondwindow.Show();
break;
case 2:
Page2 p2 = new Page2();
secondwindow.frame.Source = new Uri("p2.xaml", UriKind.Relative);
secondwindow.Show();
break;

The user should not be able to navigate between these two pages, and between choosing one or the other page, the user will have some interaction with the main window. For the user interaction with the main window, the second window gets hidden:

if (secondWindow != null)
{
secondwindow.Hide();
}

Now if the user selects the first page and and then the second page, when I show the second window, I can see the first page for a fraction of a second, and then second page gets rendered. I wanted to know if there is a way to make sure the rendering is complete before using:

secondwindow.Show();