将焦点放在WPF中的自定义（用户）控件上

<Window x:Class=\"WpfApplication14.MainWindow\"
        xmlns=\"http://schemas.microsoft.com/winfx/2006/xaml/presentation\"
        xmlns:x=\"http://schemas.microsoft.com/winfx/2006/xaml\"
        Title=\"MainWindow\" Height=\"350\" Width=\"525\"
        PreviewKeyDown=\"Window_PreviewKeyDown\">
    <Grid>
        <TextBox Name=\"textBox1\" 
                 Margin=\"91,66,292,223\" Width=\"120\" 
                 Text=\"Good morning, miss Hilton!\"/>
        <Canvas Name=\"canvas1\" Focusable=\"True\"
                Margin=\"124,112,179,99\" Width=\"200\"
                Background=\"AliceBlue\"
                MouseDown=\"canvas1_MouseDown\"
                PreviewKeyDown=\"canvas1_PreviewKeyDown\"  />
    </Grid>
</Window>

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void canvas1_MouseDown(object sender, MouseButtonEventArgs e)
    {
        Console.WriteLine(\"canvas_MouseDown 0, canvas1.IsFocused? {0}\",
            canvas1.IsFocused);

        canvas1.Focus();

        Console.WriteLine(\"canvas_MouseDown 1, canvas1.IsFocused? {0}\",
            canvas1.IsFocused);
    }

    private void canvas1_PreviewKeyDown(object sender, KeyEventArgs e)
    {
        Console.WriteLine(\"canvas_PreviewKeyDown, canvas1.IsFocused? {0}\",
            canvas1.IsFocused);

        if (canvas1.IsFocused)
            MoveCanvas(e.Key);
    }

    private void Window_PreviewKeyDown(object sender, KeyEventArgs e)
    {
        //Console.WriteLine(\"Window_PreviewKeyDown, canvas1.IsFocused? {0}\",
        //    canvas1.IsFocused);

        //if (canvas1.IsFocused)
        //    MoveCanvas(e.Key);
    }

    void MoveCanvas(Key key)
    {
        int delta = 10;
        switch (key)
        {
            case Key.Left: canvas1.Margin = new Thickness(
                canvas1.Margin.Left - delta,
                canvas1.Margin.Top,
                canvas1.Margin.Right,
                canvas1.Margin.Bottom);
                break;
            case Key.Up: canvas1.Margin = new Thickness(
                canvas1.Margin.Left,
                canvas1.Margin.Top - delta,
                canvas1.Margin.Right,
                canvas1.Margin.Bottom + delta);
                break;
            case Key.Right: canvas1.Margin = new Thickness(
                canvas1.Margin.Left,
                canvas1.Margin.Top,
                canvas1.Margin.Right - delta,
                canvas1.Margin.Bottom);
                break;
            case Key.Down: canvas1.Margin = new Thickness(
                canvas1.Margin.Left,
                canvas1.Margin.Top + delta,
                canvas1.Margin.Right,
                canvas1.Margin.Bottom - delta);
                break;
            default:
                break;
        }
    }
}

   canvas_MouseDown 0, canvas1.IsFocused? False \' before click \'
   canvas_MouseDown 1, canvas1.IsFocused? True  \' after click \' 
Window_PreviewKeyDown, canvas1.IsFocused? True  \' up 1 \'
canvas_PreviewKeyDown, canvas1.IsFocused? True  \' up 1 \'
Window_PreviewKeyDown, canvas1.IsFocused? False \' up 2 \'
Window_PreviewKeyDown, canvas1.IsFocused? False \' up 3 \'