Wpf event when DataContext is modified

Question

You know how a TextBox will have its content modified when the DataContext changes (not replaced, just modified)? Well I want to be notified just like the UI is, with some sort of event on the DataContext. So far, I haven't found a way to do this, and I'm about to give up and simply subscribe to all the events on each INotifyPropertyChanged in my DataContext. I know there's the DataContextChanged / DataContextChanging in the Window class, but so far I either can't get it to work, or this only fires when the DataContext is replaced completely. Is there a way to do this?

Answer 1

Think about what is being asked. If any property changes on a data context a general event is to fire.

What process is available which can do that operation externally ?

Decentralized Solution

Properties do not provide a change notification unless they are manually programmed to do so themselves; hence why INotifyPropertyChange is the route to normally use.

Centralized Solution

Otherwise a separate manager will need to reflect off of the instance taking a snapshot of all the properties. Then on a timer the manager will poll the instance for a current snapshot and compare that one to the old snapshot. If a change is detected an event can be fired and the new snapshot replaces the old.

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Answer 2

DataContextChanged event is only fired when the DataContext of the Window has changed completely (set to null, or a new instance, etc.). I believe you are down the correct path, and inside your ViewModel, you will need to subscribe to NotifyPropertyChanged . In the event handler, you can switch on the corresponding property like so:

private void OnNotifyPropertyChanged(object sender, PropertyChangedEventArgs e)
{
    switch (e.Property)
    {
        case "Property1":
            break;
        case "Property2":
            break;
        case "Property3":
            break;
    }
}