ViewModel event fires multiple times

Question

I'm using MVVM Light for my application and I have also implemented the INavigationService for going back/for between pages.

So in a common scenario, it's like this

MainPage > Categories > Rounds > DataPage.

In the DataPage, I'm making a request to fetch the results and depending on the result returned from the callback I call the .GoBack() method to pop the current page from the stack and return to Rounds.

What I have noticed is that if I hit first the DataPage and the .GoBack() gets called and then tap on a different round the callback method will be fired twice, and if I go back and in again thrice, and continues like this.

Essentially this means that the .GoBack() will be called again and the navigation gets messed up.

I believe this has to do with not cleaning up the previous VM's, I tried changing this behavior with the UnRegister / Register class from SimpleIOC but no luck.

Sounds like you're hooking up the event when you enter but not unhooking it when you leave. I'd remove the callback from the event inside the callback. — Slepz
@Slepz I was trying to do that and did it another way now, check my proposed answer and tell me your comment. — Dimitris Batsougiannis

Dimitris Batsougiannis Dimitris Batsougiannis · Accepted Answer · 2017-06-01T18:58:38

In the ViewModel class

public void UnsubscribeFromCallBack()
{
  this.event -= method;
}

In the .xaml.cs page

    protected override void OnDisappearing()
    {
        base.OnDisappearing();
        PageViewModel vm = (this.BindingContext as PageViewModel);
        vm.UnSubscribeFromCallback();
    }

ViewModel event fires multiple times

1 Answers