How to process CollectionView On SelectedItem event in ViewModel Code instead of Back-end Code of Content Page? Xamarin.Form

Question

I want to get data from the SelectedItem in CollectionView, but doing that I must work with SelectionChanged_EventHandler(object sender, SelectionChangedEventArgs e) which appear to be inside the Back-end code of the Content Page. I want to process this work inside my ViewModel code instead as I have to pass the data from SelectedItem to my ObservableCollection<> in the ViewModel code.

Is there any method that I can get data from the SelectedItem in CollectionView and also handle this event inside my ViewModel code?

Answer 1

Yes! There are several ways to do this:

1) Using SelectedItem Bindeable property to trigger the event

XAML:

<CollectionView
            SelectedItem="{Binding SelectedItem}" ..../>

ViewModel:

public Item SelectedItem
        {
            get { return _selectedItem; }
            set
            {
                if (value == _selectedItem)
                    return;

                _selectedItem = value;
                TriggerMethodThatYouWant();
                OnPropertyChanged(nameof(BackgroundTest));
            }
        }

2) Using a TapGestureRecognizer: this will trigger On Tapping, is different that selection but achieves the same

Xaml:

<CollectionView
                ItemsSource="{Binding Items}">
                <CollectionView.ItemTemplate>
                    <DataTemplate>
                        <StackLayout>
                            <StackLayout.GestureRecognizers>
                                <TapGestureRecognizer Command="{Binding tapCommand}" CommandParameter="{Binding .}"/>
                            </StackLayout.GestureRecognizers>
                      </DataTemplate>
                 </CollectionView.ItemTemplate>
<CollectionView>

Viewmodel: You will have to create the command and the method

    public Command<Item> tapCommand { get; }