I run in a trouble. WPF, compiled XAML: on changed text handler run but not all controls initizlzed

Question

Answer 1

Try this:

private void textBox1_TextChanged( object sender, TextChangedEventArgs e )
{
    if( !IsLoaded ) return;

    Debug.Assert( textBox2 != null );
    textBox2.Text = textBox1.Text;
}

If required, handle the Loaded event of window too:

private void Window_Loaded( object sender, RoutedEventArgs e )
{
    textBox2.Text = textBox1.Text;
}