WPF and initial focus

Question

This works, too:

<Window FocusManager.FocusedElement="{Binding ElementName=SomeElement}">

   <DataGrid x:Name="SomeElement">
     ...
   </DataGrid>
</Window>

I had the bright idea to dig through Reflector to see where the Focusable property is used, and found my way to this solution. I just need to add the following code to my Window's constructor:

Loaded += (sender, e) =>
    MoveFocus(new TraversalRequest(FocusNavigationDirection.First));

This will automatically select the first control in the tab order, so it's a general solution that should be able to be dropped into any window and Just Work.

Based on the accepted answer implemented as an attached behavior:

using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;

namespace UI.Behaviors
{
    public static class FocusBehavior
    {
        public static readonly DependencyProperty FocusFirstProperty =
            DependencyProperty.RegisterAttached(
                "FocusFirst",
                typeof(bool),
                typeof(FocusBehavior),
                new PropertyMetadata(false, OnFocusFirstPropertyChanged));

        public static bool GetFocusFirst(Control control)
        {
            return (bool)control.GetValue(FocusFirstProperty);
        }

        public static void SetFocusFirst (Control control, bool value)
        {
            control.SetValue(FocusFirstProperty, value);
        }

        static void OnFocusFirstPropertyChanged(
            DependencyObject obj, DependencyPropertyChangedEventArgs args)
        {
            Control control = obj as Control;
            if (control == null || !(args.NewValue is bool))
            {
                return;
            }

            if ((bool)args.NewValue)
            {
                control.Loaded += (sender, e) =>
                    control.MoveFocus(new TraversalRequest(FocusNavigationDirection.Next));
            }
        }
    }
}

Use it like this:

<Window xmlns:Behaviors="clr-namespace:UI.Behaviors"
        Behaviors:FocusBehavior.FocusFirst="true">

I found another possible solution. Mark Smith posted a FirstFocusedElement markup extension for use with FocusManager.FocusedElement.

<UserControl x:Class="FocusTest.Page2"
    xmlns:FocusTest="clr-namespace:FocusTest"
    FocusManager.FocusedElement="{FocusTest:FirstFocusedElement}">