Question

I have a UserControl that contains a TextBox. When the user control becomes visible, I give the TextBox focus. Could somebody clarify why I have to do this using the Dispatcher?

public MyUserControl() 
{
    InitializeComponent();
    this.IsVisibleChanged += VisibilityChanged;
}

Case 1 (works):

private void VisibilityChanged(object sender, DependencyPropertyChangedEventArgs e)
{
    if (this.Visibility == Visibility.Visible)
    {
        this.Dispatcher.BeginInvoke((Action)delegate
        {
            Keyboard.Focus(this.InputTextBox);
        }, DispatcherPriority.Render);
    }
}

Case 2 (does not work):

private void VisibilityChanged(object sender, DependencyPropertyChangedEventArgs e)
{
    if (this.Visibility == Visibility.Visible)
    {
        Keyboard.Focus(InputTextBox);
    }
}

Answer 1

could you call Keyboard.Focus(InputTextBox); in the event handler for InputTextBox.IsVisibleChanged instead of this.IsVisibleChanged?

If this works then I suspect the this.IsVisibleChanged event is raised before the layout panel has updated the children controls, i.e perhaps InputTextBox is still not visible when you put focus on it without BeginInvoke.