In WPF, I've three objects exposing the same DependencyProperty (let's say it's an integer). I want all three property values to remain synchronized, i.e. that whenever the int value changes in an object, this value is propagated to the two other objects. I think of multibinding to do the job, but I don't know how to detect which object changed, thus which value should be used and propagated to the other objects.

Edited: here is my tentative code for multibinding, with the false hope that it would work without additional code:

// create the multibinding
MultiBinding mb = new MultiBinding() {
    Mode = BindingMode.TwoWay,
    UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged
};

// create individual bindings to associate object_2 and object_3 to object_1
Binding b2 = new Binding() {
    Source = object_2,
    Path = new PropertyPath("X")
};
Binding b3 = new Binding() {
    Source = object_3,
    Path = new PropertyPath("X")
};

// add individual bindings to multibinding
mb.Bindings.Add(b2);
mb.Bindings.Add(b3);

// bind object_2 and _3 to object_1
BindingOperations.SetBinding(object_1, TypeObject_1.XProperty, mb);

But actually, there is a runtime error, saying the binding set by the last instruction is lacking a converter. But again I don't know how to write this converter (there is nothing to convert (as this is the case in the related MS sample of code linking 3 rgb properties to a color property), only to forward the value of the property changed to the two other properties).

I understand I could solve the problem by creating an X_Changed event in the 3 types and then have each object registering to the two other objects event. I don't like this "manual" way and would prefer to bind the 3 properties together.