ISupportIncrementalLoading Interface
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Specifies a calling contract for collection views that support incremental loading.
public interface class ISupportIncrementalLoading
/// [Windows.Foundation.Metadata.ContractVersion(Windows.Foundation.UniversalApiContract, 65536)]
/// [Windows.Foundation.Metadata.Guid(2136926610, 30356, 20076, 165, 27, 227, 75, 244, 61, 231, 67)]
struct ISupportIncrementalLoading
[Windows.Foundation.Metadata.ContractVersion(typeof(Windows.Foundation.UniversalApiContract), 65536)]
[Windows.Foundation.Metadata.Guid(2136926610, 30356, 20076, 165, 27, 227, 75, 244, 61, 231, 67)]
public interface ISupportIncrementalLoading
Public Interface ISupportIncrementalLoading
- Attributes
Device family |
Windows 10 (introduced in 10.0.10240.0)
|
API contract |
Windows.Foundation.UniversalApiContract (introduced in v1.0)
|
The following code example demonstrates how to implement this interface. For the complete code listing, see the XAML data Binding sample.
#pragma region Overridable methods
virtual Concurrency::task<Windows::Foundation::Collections::IVector<Platform::Object^>^> LoadMoreItemsOverride(Concurrency::cancellation_token c, unsigned int count)
{
return Concurrency::task<Windows::Foundation::Collections::IVector<Platform::Object^>^>(
[=]() -> Windows::Foundation::Collections::IVector<Platform::Object^>^ {
auto items = ref new Platform::Collections::Vector<Platform::Object^>();
return items;
});
}
virtual bool HasMoreItemsOverride()
{
return false;
}
#pragma endregion
IncrementalLoadingBase()
{
_storage = ref new Platform::Collections::Vector<Platform::Object^>();
_storage->VectorChanged += ref new Windows::Foundation::Collections::VectorChangedEventHandler<Platform::Object^>(this, &IncrementalLoadingBase::_storageVectorChanged);
_busy = false;
_isVectorChangedObserved = false;
}
public:
virtual Windows::Foundation::IAsyncOperation<Windows::UI::Xaml::Data::LoadMoreItemsResult>^ LoadMoreItemsAsync(unsigned int count)
{
if (_busy)
{
throw ref new Platform::FailureException("Only one operation in flight at a time");
}
_busy = true;
return Concurrency::create_async([=](Concurrency::cancellation_token c) {
return LoadMoreItemsAsync(c, count)
.then([=](Windows::UI::Xaml::Data::LoadMoreItemsResult result) -> Windows::UI::Xaml::Data::LoadMoreItemsResult {
_busy = false;
return result;
});
});
}
property bool HasMoreItems
{
virtual bool get() { return HasMoreItemsOverride(); }
}
#pragma endregion
#region ISupportIncrementalLoading
public bool HasMoreItems
{
get { return HasMoreItemsOverride(); }
}
public Windows.Foundation.IAsyncOperation<LoadMoreItemsResult> LoadMoreItemsAsync(uint count)
{
if (_busy)
{
throw new InvalidOperationException("Only one operation in flight at a time");
}
_busy = true;
return AsyncInfo.Run((c) => LoadMoreItemsAsync(c, count));
}
#endregion
#region INotifyCollectionChanged
public event NotifyCollectionChangedEventHandler CollectionChanged;
#endregion
#region Private methods
async Task<LoadMoreItemsResult> LoadMoreItemsAsync(CancellationToken c, uint count)
{
try
{
var items = await LoadMoreItemsOverrideAsync(c, count);
var baseIndex = _storage.Count;
_storage.AddRange(items);
// Now notify of the new items
NotifyOfInsertedItems(baseIndex, items.Count);
return new LoadMoreItemsResult { Count = (uint)items.Count };
}
finally
{
_busy = false;
}
}
void NotifyOfInsertedItems(int baseIndex, int count)
{
if (CollectionChanged == null)
{
return;
}
for (int i = 0; i < count; i++)
{
var args = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, _storage[i + baseIndex], i + baseIndex);
CollectionChanged(this, args);
}
}
#endregion
#region Overridable methods
protected abstract Task<IList<object>> LoadMoreItemsOverrideAsync(CancellationToken c, uint count);
protected abstract bool HasMoreItemsOverride();
#endregion
#region State
List<object> _storage = new List<object>();
bool _busy = false;
#endregion
Has |
Gets a sentinel value that supports incremental loading implementations. |
Load |
Initializes incremental loading from the view. |