ISupportIncrementalLoading Interface

Definition

Namespace:

Microsoft.UI.Xaml.Data

Specifies a calling contract for collection views that support incremental loading.

public interface class ISupportIncrementalLoading

/// [Windows.Foundation.Metadata.ContractVersion(Microsoft.UI.Xaml.WinUIContract, 65536)]
/// [Windows.Foundation.Metadata.Guid(3640243590, 42570, 24568, 134, 142, 32, 78, 20, 79, 44, 244)]
struct ISupportIncrementalLoading

[Windows.Foundation.Metadata.ContractVersion(typeof(Microsoft.UI.Xaml.WinUIContract), 65536)]
[Windows.Foundation.Metadata.Guid(3640243590, 42570, 24568, 134, 142, 32, 78, 20, 79, 44, 244)]
public interface ISupportIncrementalLoading

Public Interface ISupportIncrementalLoading

Attributes

ContractVersionAttribute GuidAttribute

Examples

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 

Properties

HasMoreItems

Gets a sentinel value that supports incremental loading implementations.

Methods

LoadMoreItemsAsync(UInt32)

Initializes incremental loading from the view.

See also

• Binding
• XAML data Binding sample
• Data binding in depth