How can I trigger an event of a (sealed) Windows Form Component programmatically?

Question

To be more specific: I want a unit test to trigger SaveFileDialog's FileOk event in order to test whether my own code (which wraps SFD and does some additional things before and after ShowDialog) is working as intended.

Thanks in advance for any help on this.

Answer 1

If you hide the SaveFileDialog behind an interface, you can use a stub or mock implementation to test your code. I would not recommend using real forms or controls in unit tests, because most of them have a hard dependency on an active message loop.

public interface ISaveFileDialog
{
    event CancelEventHandler FileOk;
}

public class SaveFileDialogStub : ISaveFileDialog
{
    public event CancelEventHandler FileOk;

    public void RaiseFileOk(CancelEventArgs e)
    {
        FileOk(this, e);
    }
}

public class ClassUnderTest
{
    public ClassUnderTest(ISaveFileDialog dialog)
    {
        dialog.FileOk += OnFileOk;
    }

    void OnFileOk(object sender, CancelEventArgs e)
    {
        //...
    }
}

Answer 2

The trouble is, events don't expose a "raise" operation* - they expose "subscribe" and "unsubscribe". It's up to the implementation how they implement subscribe/unsubscribe.

However, in the case of SaveFileDialog (or any FileDialog) there's the OnFileOk protected method which will raise the event. You could either derive from SafeFileDialog and expose a public method which will call OnFileOk or just call OnFileOk using reflection. That will then call the event handlers for FileOk. I'm not sure I particularly like either of these plans of attack, but without more information about what you're trying to do I thought I'd just answer the question instead of questioning too much :)

---

* In fact, .NET itself does have the idea of the "raise" part of an event, hence EventInfo.GetRaiseMethod. However, this goes against the general idea of an event IMO, and the C# compiler never generates the raise part. I don't believe the standard libraries usually expose it either.

Answer 3

I believe it might be possible to use PrivateObject to invoke a private/protected method on your class.