Event fires more and more times

Question

I have a silverlight mvvm application that loads main view with 2 user controls loaded into 2 ContentControls, one with listbox showing items and other with edit button. Whe

Answer 1

You can't use lambdas when you want to unregister from events.

this.globalEvents.OnSaveButtonClicked += (s, e) => SaveData(); 

This will create one instance - let's call it instance A - of type EventHandler and add it as a handler.

this.globalEvents.OnSaveButtonClicked -= (s, e) => SaveData(); 

This will not remove instance A from the event but create a new instance - instance B - and tries to remove it from the event.

To fix this problem, either create a little method or save that anonymous method in a field:

class ViewModel
{

    private EventHandler _saveButtonClickedHandler;
    // ...

    public ViewModel()
    {
        _saveButtonClickedHandler = (s, e) => SaveData();
        this.globalEvents.OnSaveButtonClicked += _saveButtonClickedHandler;
        // ...
    }

    public void Dispose()
    {
        this.globalEvents.OnSaveButtonClicked -= _saveButtonClickedHandler;
        // ...
    }

    // ...
}