Question

I am trying to find a way to remove an activity from the stack- We have a flow in our app: activity/viewmodel a -> activity/viewmodel b ->activity/viewmodel c. In c the user have the posibility of choosing a date or go back. If he goes back he should be returned to b. However if he chooses a date he is fowarded to a new instance of activity/viewmodel b and the “old” instance of activity/viewmodel b is obsolete and should be removed.

A suggestion from Stuart Lodge (on a similar thread, just for mono touch) was to use RequestRemoveBackStep() but I am not sure how to use it and I cant find an example.

Can anyone point me in the right direction?

Regards

Answer 1

The RequestRemoveBackStep() method is a member of the IMvxViewDispatcher interface and is implemented on some platforms:

public interface IMvxViewDispatcher : IMvxMainThreadDispatcher
{
    bool RequestNavigate(MvxShowViewModelRequest request);
    bool RequestClose(IMvxViewModel whichViewModel);
    bool RequestRemoveBackStep();
}

from https://github.com/slodge/MvvmCross/blob/vnext/Cirrious/Cirrious.MvvmCross/Interfaces/Views/IMvxViewDispatcher.cs

However, its not entirely simple to always do this… so on Droid, for example, it is currently implemented as:

    public bool RequestRemoveBackStep()
    {
        // not supported on Android? Not sure how to do this currently...
        return false;
    }

from https://github.com/slodge/MvvmCross/blob/vnext/Cirrious/Cirrious.MvvmCross.Droid/Views/MvxAndroidViewDispatcher.cs

There are issues logged about this functionality – e.g. https://github.com/slodge/MvvmCross/issues/80 – but it seems likely that this functionality might simply be dropped from future Mvx implementations – especially as it’s not very easy to do for every view on every platform.

---

If you need this type of functionality now, then you’ll need to find your own way of implementing this functionality… depending on what your specific use case is (sorry – the details of your current use case aren’t clear to me from the question).

There are several technical routes available including:

• using NoHistory flags
• using RequestClose(oldviewModel) calls
• adding logic to your Presenter
• using a Messenger to request views close themselves.