C# button up/down/left/right not detected : <p>A week ago I used this for detecting the <code>up/down/left/right keys</code> in my 
wpf application:</p>

<pre><code>private void Invaders_KeyDown(object sender, KeyEventArgs e)
{
    MessageBox.Show(e.KeyCode.ToString());
    switch (e.KeyCode.ToString())
    {
        case "Up":
            MessageBox.Show("Up");
            break;
        case "Down":
            MessageBox.Show("Down");
            break;
        case "Left":
            MessageBox.Show("Left");
            break;
        case "Right":
            MessageBox.Show("Right");
            break;
    }
}
</code></pre>

<p>But today I started a new application and this does not work anymore? It detects everything except <code>up/down/left/right</code>. What could be going on here?</p>
