Raise event when stubbed property is changed

[yordans]

How to raise event when stubbed property (automatically tracking its value) is changed (setter called)?

e.g.
mock.SetupProperty(m => m.Foo).Raises(m => m.FooChanged += null);
mock.Object.Foo = 5; // raises the FooChanged event on ISomething

[yordans]

I want the event to be fired automatically when a stubbed property is changed but it seems that this functionality is missing.

[stakx]

@yordans - It appears that you've already answered your own question for the most part:

public interface IFoo
{
    int Foo { get; set; }
    event EventHandler FooChanged;
}

var mock = new Mock<IFoo>();
mock.Object.FooChanged += (s, e) => Console.WriteLine("Foo property changed.");
mock.SetupSet(m => m.Foo = It.IsAny<int>()).Raises(m => m.FooChanged += null, EventArgs.Empty);
mock.Object.Foo = 5;

The above will fire the event whenever the property is set, not when it is changed. If you want the latter, you'll need something more elaborate:

int value = default(int);  // this will act as the "backing field" for the property
mock.SetupGet(m => m.Foo).Returns(() => value);
mock.SetupSet(m => m.Foo = It.IsAny<int>()).Callback((int newValue) =>
{
    bool shouldRaiseChangedEvent = newValue != value;
    value = newValue;
    if (shouldRaiseChangedEvent)
    {
        mock.Raise(m => m.FooChanged += null, EventArgs.Empty);
    }
});

Not so different from how you'd implement INotifyPropertyChanged. (SetupProperty is actually implemented in a very similar way to the above, it just lacks the logic to determine value changes and trigger an event.)

If you want an API that creates such a setup for any pair of a property P and an event PChanged, it should be easy to create it as an extension method. Because neither the member names nor the property type will be known in advance, you'll have to build the expressions for Setup and Raise yourself (using the static Expression factory methods) instead of letting the compiler do it for you.

Does this answer your question?

[yordans]

It is fine the event to be fired when the property is set, but the real problem is that I want the mock to "track" sets/gets to this property (i.e. Stub) + firing event.

mock.SetupSet(m => m.Foo = It.IsAny<int>())

won't track the property Foo.

[stakx]

What exactly do you mean by "tracking a property"?

sets/gets to this property (i.e. Stub) + firing event

Did you notice the second part of my above post? Because that's exactly what it does.

[yordans]

When setup property in this way:
mock.SetupProperty(m => m.Foo);
it is a Stub and it tracks its changes, so if latter call mock.Object.Foo = 5 and then get the value, it will be 5.

And the question is could this kind of stubbed property be setup to raise an event when changed?

[stakx]

And the question is could this kind of stubbed property be setup to raise an event when changed?

I'll once again refer you to my first post above which shows you just how to do that. (And no, SetupProperty currently doesn't offer a way to do this out of the box.)

[yordans]

Thank you for your responses. I think the issue can be closed.

Is it planned SetupProperty to offer a way for raising events out of the box?

[stakx]

Is it planned SetupProperty to offer a way for raising events out of the box?

No, such an extension isn't planned at the moment.

[jhv2017kam]

@stakx When implementing what you describe here I ran in to the problem that property.ToPropertyInfo(); used in the newest version of SetupProperty is placed in an internal extensions class would it be possible to have ToProperty be part of the public API?

[stakx]

@jhv2017kam, no, that helper method definitely does not belong in Moq's public API... it's strictly an implementation detail. But it should be easy enough to replicate in your own code.