To get a dynamic “paged” loading for your list view, follow the steps below:
Make a new usercontrol in your forms project. Derive from ContentView instead from ListView. By deriving from listview, you simply can not Count the items binded to the ItemsSource property, which is the base of the Fetching logic.
public class InfiniteScrollListView : ContentView
Make a countable ItemsSource bindable property for your new usercontrol.
public static readonly BindableProperty ItemsSourceProperty = BindableProperty.Create(
propertyName: "ItemsSource",
returnType: typeof(IList),
declaringType: typeof(View),
defaultValue: null,
defaultBindingMode: BindingMode.TwoWay,
propertyChanged: null);
public IList ItemsSource
{
get { return (IList)GetValue(ItemsSourceProperty); }
set { SetValue(ItemsSourceProperty, value); }
}
We need to get the usercontrol to display a listview for us. Make a new instance of a listview. You can specify a caching strategy for the listview, which can be useful on lists have a lot of items. Set the contenview’s content to the new listview instance.
public InfiniteScrollListView()
{
_listViewInstance = new ListView(cachingStrategy: ListViewCachingStrategy.RecycleElement);
_listViewInstance.HorizontalOptions = LayoutOptions.Fill;
_listViewInstance.VerticalOptions = LayoutOptions.Fill;
_listViewInstance.ItemAppearing += InfiniteScrollListView_ItemAppearing;
_listViewInstance.SetBinding(ListView.ItemsSourceProperty, new Binding(nameof(ItemsSource), BindingMode.TwoWay, source: this));
Content = _listViewInstance;
}
~InfiniteScrollListView()
{
if (_listViewInstance != null)
_listViewInstance.ItemAppearing -= InfiniteScrollListView_ItemAppearing;
}
The ItemAppearing event is the most important event in our Infinite scrolling listview instance. It’s called, when an item is displayed “phisically” on the screen. Let’s make an eventhandler for it. We are using a new Bindable Property for fetching data command, which will be called, when the last item of the ItemsSource has been displayed, and an another Bindable property, to turn off the fetching if the Data access layer could not provide more elements for the query. The _lastElementIndex will be the e.ItemIndex.
if (_lastItemDisplayedIndex == (ItemsSource?.Count - 1 ?? int.MinValue))
{
if (HasMoreItems)
{
if (FetchDataCommand?.CanExecute(null) == true)
{
FetchDataCommand?.Execute(null);
}
}
}