Nrthugu

I have this code that attaches: OnTabbarControllerItemSelected; to tabbarController.ViewControllerSelected. From what I understand events like this that are attached should also be detached later.

Can someone give me advice on where I should do the detach. Also should I override the Dispose method for this code and if so how should I do that?

Code:

    protected override void OnElementChanged(VisualElementChangedEventArgs e)

    {

        base.OnElementChanged(e);



        if (e.NewElement != null)

        {

            _page = (MainPage)e.NewElement;

        }

        else

        {

            _page = (MainPage)e.OldElement;

        }



        if (e.OldElement != null)

        {

            Xamarin.Forms.Application.Current.PropertyChanged -= Current_PropertyChanged;

            return;

        }



        try

        {

            var tabbarController = (UITabBarController)this.ViewController;



            if (null != tabbarController)

            {

                Xamarin.Forms.Application.Current.PropertyChanged += Current_PropertyChanged; //subscribe to the App class' built in property changed event

                tabbarController.ViewControllerSelected += OnTabbarControllerItemSelected;



                UpdateTheme();

            }

        }

        catch (Exception exception)

        {

            Console.WriteLine(exception);

        }

    }

Would appreciate some advice on how I can detach this method in a similar way to the way that the Current_PropertyChanged method is being detached.

Have you tried tabbarController.ViewControllerSelected -= OnTabbarControllerItemSelected;?

From my understanding, event handler is just a delegate, a normal reference-type object under the control of GC. It doesn't need to be manually detached if it remains valid until the GC collects the event itself. This should be true in most cases (e.g. a handler inside the same window).

It's possible that you need to detach manually. That happens when a child object is listening to an event of parent object. If the child object could be Disposed before the parent, the handler becomes invalid (as it might refer to the disposed child object). In this case, you should always know when it becomes invalid (in the above case, the Dispose of the child object), and that's when and where you should detach it.

EDIT
From the code you provided it's not easy to tell but it's more likely you don't need to detach OnTabbarControllerItemSelected. But you probably need to be careful to Xamarin.Forms.Application.Current.PropertyChanged.

Also see this question.