MvvmCross MvxSpinner does not update after re-entering

Question

Resolved

Please, I need some help!

Android Situation:

MSVisualStudio 2015 + Xamarin + Mvvmcross 4.4

One Activity and Several Fragments. Using default presenter.

1- View (Fragment) with MvxRecyclerView, a row is selected for editing.

2- Show new view (Fragment) with a MvxSpinner, and change its value (A) to another one (B). Remember: A & B are objects.

<Mvx.MvxSpinner
    android:id="@+id/spinner_academic_start_week"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    local:MvxDropDownItemTemplate="@layout/spinner_basic"
    local:MvxItemTemplate="@layout/item_spinner_basic"
    local:MvxBind="ItemsSource AcademicYearWeeksCollection; SelectedItem AcademicStartWeek; HandleItemSelected SelectAcademicStartWeekCommand" />

and there is a ViewModel with

public IList<AcademicYearWeeks> AcademicYearWeeksCollection { get { return _academicYearWeeksCollection; } }

where AcademicYearWeeks is a class with properties and so on.

3- Cancel edition and return to View with MvxRecyclerView.

4- Repeat click for edit same row.

5- Oooppps! Spinner shows B not A. Why????

Other considerations:

Fragment with spinner always is called using

ShowViewModel<CourseViewModel>(
    new
     {
        courseId = item.CourseId
     });

and its ViewModel associated

public void Init(int courseId)
{
    _courseId = courseId;
}

public override void Start()
{
    base.Start();

    LoadAcademicYearWeeksCollection();

    if (_courseId == 0)
        NewCourse();
    else
        LoadCourse();
}

and is closed using

Close(this)

I'll be very greatful!

Thanks.

Answer 1

When you create a fragment using MvxFragment attribute, by default the IsCacheableFragment is set to true. Therefore, as the fragment and it ViewModel are being cached and you get the behaviour you are experiencing when returning to the page for a second time.

Ideally you should just be able to set the IsCacheableFragment to false

[MvxFragment(typeof(MainViewModel), Resource.Id.content_frame,
    IsCacheableFragment = false)]

However, the behaviour of this feature is, I believe, undesired. As according to GitHub issue it sets your ViewModel to null.

Another approach you can try it to force the fragment and ViewModel pair to refresh themselves. In your fragments parent activity override ShowFragment and set the forceAddToBackStack to true for your ViewModel with the spinner on it

protected override void ShowFragment(string tag, int contentId, Bundle bundle, bool forceAddToBackStack = false, bool forceReplaceFragment = false)
{
    if (tag.Equals(typeof(<<Your View Model Type>>).FullName))
        forceReplaceFragment = true;

    base.ShowFragment(tag, contentId, bundle, forceAddToBackStack, forceReplaceFragment);
}