So the problem is that I was using xamarin forms listview and everything was working fine. Now I've decided to switch to sflistview and when I implemented group header template, the listview was empty. Here are the codes.
XAML.
<syncfusion:SfListView.GroupHeaderTemplate>
<DataTemplate>
<ViewCell>
<Label Text="{x:Binding Key}" />
</ViewCell>
</DataTemplate>
</syncfusion:SfListView.GroupHeaderTemplate>
Code behind.
var groupedData = return_response_data.OrderBy(x => x.Months)
.ThenByDescending(x => x.Days)
.GroupBy(x => x.DateSet)
.Select(x => new ObservableGroupCollection<string, PhotoModel>(x))
.ToList();
var binding = new ObservableCollection<ObservableGroupCollection<string, PhotoModel>>(groupedData);
InfoList.ItemsSource = binding;
Binding variable has two groups and 8 entries in each. My listview is showing me two empty frames right now. Don't know what's the problem. It was working fine with xamarin forms listview and I don't need group descriptor.