public static async Task ScrollIntoViewAsync(this ListViewBase listViewBase, object item)
{
var tcs = new TaskCompletionSource <object>();
//var scrollViewer = listViewBase.GetScrollViewer();
var scrollViewer = listViewBase.GetChildOfType <ScrollViewer>();
EventHandler <ScrollViewerViewChangedEventArgs> viewChanged = (s, e) => tcs.TrySetResult(null);
try {
scrollViewer.ViewChanged += viewChanged;
listViewBase.ScrollIntoView(item, ScrollIntoViewAlignment.Leading);
await tcs.Task;
} finally {
scrollViewer.ViewChanged -= viewChanged;
}
}
public async static Task ScrollToItem(this ListViewBase listViewBase, object item)
{
bool isVirtualizing = default(bool);
double previousHorizontalOffset = default(double), previousVerticalOffset = default(double);
// get the ScrollViewer withtin the ListView/GridView
//var scrollViewer = listViewBase.GetScrollViewer();
var scrollViewer = listViewBase.GetChildOfType <ScrollViewer>();
// get the SelectorItem to scroll to
var selectorItem = listViewBase.ContainerFromItem(item) as SelectorItem;
// when it's null, means virtualization is on and the item hasn't been realized yet
if (selectorItem == null)
{
isVirtualizing = true;
previousHorizontalOffset = scrollViewer.HorizontalOffset;
previousVerticalOffset = scrollViewer.VerticalOffset;
// call task-based ScrollIntoViewAsync to realize the item
await listViewBase.ScrollIntoViewAsync(item);
// this time the item shouldn't be null again
selectorItem = (SelectorItem)listViewBase.ContainerFromItem(item);
}
// calculate the position object in order to know how much to scroll to
var transform = selectorItem.TransformToVisual((UIElement)scrollViewer.Content);
var position = transform.TransformPoint(new Point(0, 0));
// when virtualized, scroll back to previous position without animation
if (isVirtualizing)
{
await scrollViewer.ChangeViewAsync(previousHorizontalOffset, previousVerticalOffset, true);
}
// scroll to desired position with animation!
scrollViewer.ChangeView(position.X, position.Y, null);
}