Xamarin Android Fragment show View before ViewModel is ready - android-fragments

Question

I have a problem with await async method. I have a fragment (SalesFragment) which contains TabLayout with two fragments (FirstSalesFragment and SecondSalesFragment). When I showing SalesFragment and there is in TabLayout selected FirstSalesFragment I have there in ViewModel async method which call API and gives me some data. But problem is in FirstSalesFragment I have Microcharts layout and I want show there Chart, but main problem is my entries for chart are from async method from Api and OnCreateView method just doesnt wait for my async method in ViewModel.
My FirstSales view just show but chart is empty because OnCreateView doesnt wait for Entries... I tried OnActivityCreated or OnStart method but its same...
My SalesFragment
public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
_view = base.OnCreateView(inflater, container, savedInstanceState);
var viewPager = _view.FindViewById<ViewPager>(Resource.Id.viewpager);
if (viewPager != null)
{
var fragments = new List<MvxViewPagerFragmentInfo>
{
new MvxViewPagerFragmentInfo(ViewModel.FirstSalesTab, typeof(FirstSalesFragment), typeof(FirstSalesViewModel)),
new MvxViewPagerFragmentInfo(ViewModel.SecondSalesTab, typeof(SecondSalesFragment), typeof(SecondSalesViewModel))
};
viewPager.Adapter = new MvxCachingFragmentStatePagerAdapter(Activity, ChildFragmentManager, fragments);
}
var tabLayout = _view.FindViewById<TabLayout>(Resource.Id.tabs);
tabLayout.SetupWithViewPager(viewPager);
return _view;
}
FirstSalesViewModel:
public class FirstSalesViewModel : BaseViewModel
{
private readonly ISessionInfo _session;
private readonly IInfoMessageReporter _infoMessageReporter;
public FirstSalesViewModel()
{
_session = Mvx.Resolve<ISessionInfo>();
_infoMessageReporter = Mvx.Resolve<IInfoMessageReporter>();
}
public async Task Initialize()
{
}
public void Init()
{
Task.Run(InitializeHourlySales);
}
private async Task InitializeHourlySales()
{
// Call API async service... initialize Entries here....
}
private List<Entry> _entries;
public List<Entry> Entries
{
get { return _entries; }
set
{
_entries = value;
RaisePropertyChanged(() => Entries);
}
}
}
}
FirstSalesFragment
public class FirstSalesFragment : BaseFragment<FirstSalesViewModel>
{
protected override int FragmentId => Resource.Layout.fragment_firstsales;
private View _view;
private ChartView _chartView;
public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
_view = base.OnCreateView(inflater, container, savedInstanceState);
_chartView = _view.FindViewById<ChartView>(Resource.Id.chartView);
if (_chartView != null)
{
InitializeChart();
}
return _view;
}
private void InitializeChart()
{
var tempEntries = ViewModel.Entries;
if (tempEntries == null || tempEntries.Count == 0)
{
_chartView.Chart = null;
return;
}
var tempChart = new LineChart
{
Entries = tempEntries,
LineMode = LineMode.Straight,
LineSize = 5,
LabelTextSize = 25,
AnimationDuration = new TimeSpan(0, 0, 5),
BackgroundColor = SKColor.Parse("#EEEEEE")
};
_chartView.Chart = tempChart;
}
}

Answer 1

Do your call to your async code in OnResume which supports using async.
I've modified your code sample a bit and made a call to your ViewModel.Init() in OnResume() for FirstSalesFragment.
FirstSalesViewModel
public class FirstSalesViewModel : BaseViewModel
{
...
public async Task Init()
{
await Task.Run(InitializeHourlySales);
}
private async Task InitializeHourlySales()
{
// Call API async service... initialize Entries here....
}
.....
FirstSalesFragment
...
public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
_view = base.OnCreateView(inflater, container, savedInstanceState);
_chartView = _view.FindViewById<ChartView>(Resource.Id.chartView);
return _view;
}
public async override void OnResume()
{
base.OnResume();
await ViewModel.Init();
if (_chartView != null)
{
InitializeChart();
}
}
...