ListView WP8中的增量加载

Question

I have read the articles about how to do incremental loading when we scroll to bottom of the list view, but how to achieve lazy loading when we scroll to top of the list. I want to add more items to the top of the list when the user reaches the top. Is there any way we can achieve this.

Answer 1

Found a solution for this. Rotate both controls.

For eg->

<ListView x:Name="GridViewMain" IncrementalLoadingThreshold="2" RenderTransformOrigin="0.5,0.5"> <ListView.RenderTransform> <RotateTransform Angle="180"></RotateTransform> </ListView.RenderTransform> <ListView.ItemContainerStyle> <Style TargetType="ListViewItem"> <Setter Property="HorizontalContentAlignment" Value="Stretch"/> <Setter Property="VerticalContentAlignment" Value="Stretch"/> </Style> </ListView.ItemContainerStyle> <ListView.Resources> <DataTemplate x:Key="DataTemplateGridViewMain"> <Grid HorizontalAlignment="Stretch" Background="#FF7C1A9B" RenderTransformOrigin="0.5,0.5"> <Grid.RenderTransform> <RotateTransform Angle="180"/> </Grid.RenderTransform> <TextBlock HorizontalAlignment="Left" Text="{Binding}" VerticalAlignment="Center" FontSize="20" FontFamily="Tempus Sans ITC" /> </Grid> </DataTemplate> </ListView.Resources> <ListView.ItemTemplate> <StaticResource ResourceKey="DataTemplateGridViewMain" /> </ListView.ItemTemplate> </ListView>

Worked for me.

Answer 2

There is no built in solution.

Here's an example that checks the ListViews scroll position and loads additional items once it is at the top.

// Attach to the view changed event
_scrollViewer = listview.GetFirstDescendantOfType<ScrollViewer>();
if (_scrollViewer != null)
{
    _scrollViewer.ViewChanged += OnViewChanged;
}

And the handler.

private void OnViewChanged(object sender, ScrollViewerViewChangedEventArgs e)
{
    // If scrollviewer is scrolled up
    if (_scrollViewer.VerticalOffset < 150)
    {
        // Start loading new items...
    }
}

Handle with care:

When adding items at the top, scroll position will change.

The check is very simple, is will only work if the scrollviewer can actually scroll.