I am trying to unit test a WPF control and need to simulate key down presses. I have seen a possible solution here, however when I try to pass in a PresentationSource I keep getting a null value (from either PresentationSource.FromVisual() or PresentationSource.FromDependencyObject()) which triggers an exception.
My question is how do I get a non-null PresentationSource that I can use in unit tests?
You can extend the PresentationSource class like this:
public class FakePresentationSource : PresentationSource
{
protected override CompositionTarget GetCompositionTargetCore()
{
return null;
}
public override Visual RootVisual { get; set; }
public override bool IsDisposed { get { return false; } }
}
And use it like this:
var uiElement = new UIElement();
uiElement.RaiseEvent(new KeyEventArgs(Keyboard.PrimaryDevice, new FakePresentationSource(), 0, Key.Delete)
{
RoutedEvent = UIElement.KeyDownEvent
});
A quicker solution for unit tests is just to mock the PresentationSource object. Note that it requires an STA thread. Sample uses Moq and nunit.
[Test]
[RequiresSTA]
public void test_something()
{
new KeyEventArgs(
Keyboard.PrimaryDevice,
new Mock<PresentationSource>().Object,
0,
Key.Back);
}
Figured this out after reading this post.
Basically, you need to put your control inside a Window and call Window.Show() on it. The post mentioned an WPF bug, but I didn't encounter this in WPF 4.
After calling Window.Show(), the presentation source will no longer be null and you will be able to send keys to the control.