/// <summary>
/// Handle the LazyLoading of items
/// </summary>
/// <param name="isInitialized">Is called with Flipview's Initialization</param>
/// <returns>Task (void)</returns>
async private Task LoadNextItemAsync(bool isInitialized = true)
{
try
{
if (this.ItemsSource != null && CanIncrementalLoadigTrigger())
{
IsBusy = true;
ISupportIncrementalLoading incrementalLoadingInterface = this.ItemsSource as ISupportIncrementalLoading;
if (incrementalLoadingInterface != null)
{
if (incrementalLoadingInterface.HasMoreItems)
{
if (!isInitialized)
{
await incrementalLoadingInterface.LoadMoreItemsAsync(1);
return;
}
for (int i = 1; i <= this.IncrementalLoadingThreshold; i++)
{
await incrementalLoadingInterface.LoadMoreItemsAsync((uint)this.DataFetchSize);
}
}
}
}
}
finally
{
IsBusy = false;
}
}
private async void OnItemAppearing(object sender, ItemVisibilityEventArgs e)
{
if (itemsSource == null || incrementalLoading == null)
{
return;
}
int position = itemsSource.IndexOf(e.Item);
if (PreloadCount <= 0)
{
PreloadCount = 1;
}
int preloadIndex = Math.Max(itemsSource.Count - PreloadCount, 0);
if ((position > lastPosition || (position == itemsSource.Count - 1)) && (position >= preloadIndex))
{
lastPosition = position;
if (!incrementalLoading.IsLoadingIncrementally &&
!IsRefreshing &&
incrementalLoading.HasMoreItems)
{
await incrementalLoading.LoadMoreItemsAsync();
}
}
}
public void LoadMoreItems(uint count)
{
Debug.Assert(_loadingOperation == null, "Expected _loadingOperation == null.");
_loadingOperation = _incrementalItemsSource.LoadMoreItemsAsync(count);
if (_loadingOperation != null)
{
_loadingOperation.Completed = OnLoadingOperationCompleted;
}
}
private async void ScrollViewer_ViewChanged(object sender, ScrollViewerViewChangedEventArgs e)
{
//incremental loading
if (incrementalCollection != null &&
scroll.VerticalOffset / scroll.ScrollableHeight >= INCREMENTAL_SCROLL_FACTOR &&
!loadingIncremental &&
incrementalCollection.HasMoreItems)
{
loadingIncremental = true;
await incrementalCollection.LoadMoreItemsAsync(30); //TODO choose your pagination increment for ISupportIncrementalLoading
loadingIncremental = false;
}
}
public IncrementalLoadingFlipView()
{
this.SelectionChanged += (sender, e) =>
{
if (this.SelectedIndex == this.Items.Count - 3)
{
ISupportIncrementalLoading list = this.ItemsSource as ISupportIncrementalLoading;
if (list?.HasMoreItems == true)
{
list?.LoadMoreItemsAsync((uint)this.Items.Count);
}
}
};
}
protected override async void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
base.OnPropertyChanged(propertyName);
if (propertyName == ItemsSourceProperty.PropertyName)
{
itemsSource = ItemsSource as IList;
if (itemsSource == null)
{
throw new Exception($"{nameof(IncrementalListView)} requires that {nameof(itemsSource)} be of type IList");
}
incrementalLoading = ItemsSource as ISupportIncrementalLoading;
if (incrementalLoading == null)
{
throw new Exception($"{nameof(IncrementalListView)} requires that {nameof(itemsSource)} be of type ISupportIncrementalLoading");
}
await incrementalLoading.LoadMoreItemsAsync();
}
}
public IAsyncOperation <LoadMoreItemsResult> LoadMoreItemsAsync(uint count)
{
return(_delegate.LoadMoreItemsAsync(count));
}
/// <summary>
/// Load more items from the source
/// </summary>
/// <param name="count">number of items to load</param>
/// <returns>Async operation of LoadMoreItemsResult</returns>
/// <exception cref="NotImplementedException">Not implemented yet...</exception>
public IAsyncOperation <LoadMoreItemsResult> LoadMoreItemsAsync(uint count)
{
ISupportIncrementalLoading sil = _source as ISupportIncrementalLoading;
return(sil?.LoadMoreItemsAsync(count));
}
/// <summary>
/// Invoked to load more items from the source.
/// </summary>
/// <param name="count">number of items to load</param>
/// <returns>Async operation of LoadMoreItemsResult</returns>
public IAsyncOperation <LoadMoreItemsResult> LoadMoreItemsAsync(uint count)
{
ISupportIncrementalLoading sourceAsSupportIncrementalLoading = _sourceCollection as ISupportIncrementalLoading;
return(sourceAsSupportIncrementalLoading?.LoadMoreItemsAsync(count));
}