implement INotifyProperty changed on Static Property in WPF and Silverlight

Question

The question is how to implement INotifyPropertyChanged on a static property because the event you implement is not static, and cannot be called by a static property. Also, you cannot bind to a static property in silverlight.

I've seen this question pop up an a few forums with a variety of solutions, none of which were very satisfying.

Well, I think I've found an elegant solution, but it's so simple I feel like I must be missing something.

The answer is, to write a non-static property that accesses a static variable like so:

    private static double length;
    public double Length
    {
        get
        {
            return length;
        }
        set
        {
            length = value;
            NotifyPropertyChanged("Length");
        }
    }

I've tested it and it seems to work just fine. Am I missing something?

Answer 1

locks for multi-threading?

http://stackoverflow.com/questions/505515/c-thread-safety-with-get-set

Answer 2

Right, but it's not really a static property, is it?
it's a public instance property that uses a static backing field.
In essence, you're binding to a specific instance of a class.

Sorry, but I think you're doing it wrong.
Personally, without knowing you're scenario, I'm willing to guess that a static property binding isn't really the technical solution you need.
What's the problem you're trying to work through?
Why isn't it better addressed by a normal binding to a ViewModel?
What's the use case for doing something like this?

Personally, this looks like a perfect scenario to have a ViewModel register to a singleton service, and once a singleton event is raised change ViewModel properties.

Answer 3

Technically, you're still not binding to a static property - you're binding to an instance of the class, which is using the static field as a backing store. This will work, to some extent, but...

There is a fundamental problem with this - If you have more than one item bound to this same backing store (which seems like something you're attempting, since you're purposefully making it static), the INotifyPropertyChanged notifications will only happen on the instance where you are currently bound.

Say, for example, you had two UserControls, sitting side by side, both bound to a ViewModel containing this code. When control A sets this property, control B will never receive notifications (since it's A's INotifyPropertyChanged that runs), so it will appear out of sync.

If you really want to try to do something like this, you're probably better off having your backing store use a class that implements INotifyPropertyChanged, and "bubble" up the property through your ViewModel class. This way, multiple instances would all be notified correctly, and you could handle any multithreading/synchronization issues that might occur if necessary.

Alternatively, you may want to consider using a single instance property (with an instance field), inside of a Singleton. This, too, would give you shared notifications of your "static" property.

Answer 4

Why does the property have to be static? If it was just a regular instance property, this wouldn't be an issue.

Avoid shared mutable state when possible :)