public static async Task AnimateToItemAsync(ListViewBase list, object targetItem, ScrollToPosition scrollToPosition)
{
var scrollViewer = list.GetFirstDescendant <ScrollViewer>();
if (scrollViewer == null)
{
// If ScrollViewer is not found, do nothing.
return;
}
// ScrollToItemAsync will only scroll to the item if it actually exists in the list (that is, it has been
// been realized and isn't just a virtual item)
if (await ScrollToItemAsync(list, targetItem, scrollViewer, scrollToPosition))
{
// Happy path; the item was already realized and we could just scroll to it
return;
}
// This is the unhappy path. Because of virtualization, the item has not actually been created yet.
// So we make our best guess about the location of the item
var targetPoint = await GetApproximateTargetAsync(list, scrollViewer, targetItem);
// And then we scroll toward that position. The interruptCheck parameter will be run as we're scrolling
// to see if the item exists yet; if it does, AnimateToOffsetAsync will be canceled and we'll finish
// off with a smooth scroll to the item
await AnimateToOffsetAsync(scrollViewer, targetPoint.X, targetPoint.Y,
async() => await ScrollToItemAsync(list, targetItem, scrollViewer, scrollToPosition));
}
public static (int firstVisibleItemIndex, int lastVisibleItemIndex, int centerItemIndex) GetVisibleIndexes(ListViewBase listViewBase, ItemsLayoutOrientation itemsLayoutOrientation)
{
int firstVisibleItemIndex = -1;
int lastVisibleItemIndex = -1;
int centerItemIndex = -1;
var scrollViewer = listViewBase.GetFirstDescendant <ScrollViewer>();
var presenters = listViewBase.GetChildren <ListViewItemPresenter>();
if (presenters != null || scrollViewer == null)
{
int count = 0;
foreach (ListViewItemPresenter presenter in presenters)
{
if (CollectionViewExtensions.IsListViewItemVisible(presenter, scrollViewer, itemsLayoutOrientation))
{
if (firstVisibleItemIndex == -1)
{
firstVisibleItemIndex = count;
}
lastVisibleItemIndex = count;
}
count++;
}
centerItemIndex = (lastVisibleItemIndex + firstVisibleItemIndex) / 2;
}
return(firstVisibleItemIndex, lastVisibleItemIndex, centerItemIndex);
}
async Task JumpTo(ListViewBase list, object targetItem, ScrollToPosition scrollToPosition)
{
var tcs = new TaskCompletionSource <object>();
void ViewChanged(object s, ScrollViewerViewChangedEventArgs e) => tcs.TrySetResult(null);
var scrollViewer = list.GetFirstDescendant <ScrollViewer>();
try
{
scrollViewer.ViewChanged += ViewChanged;
if (scrollToPosition == ScrollToPosition.Start)
{
list.ScrollIntoView(targetItem, ScrollIntoViewAlignment.Leading);
}
else if (scrollToPosition == ScrollToPosition.MakeVisible)
{
list.ScrollIntoView(targetItem, ScrollIntoViewAlignment.Default);
}
else
{
// Center and End are going to be more complicated.
}
await tcs.Task;
}
finally
{
scrollViewer.ViewChanged -= ViewChanged;
}
}
public static async Task JumpToItemAsync(ListViewBase list, object targetItem, ScrollToPosition scrollToPosition)
{
var scrollViewer = list.GetFirstDescendant <ScrollViewer>();
var tcs = new TaskCompletionSource <object>();
Func <Task> adjust = null;
async void ViewChanged(object s, ScrollViewerViewChangedEventArgs e)
{
if (e.IsIntermediate)
{
return;
}
scrollViewer.ViewChanged -= ViewChanged;
if (adjust != null)
{
// Handle adjustments for non-natively supported scroll positions
await adjust();
}
tcs.TrySetResult(null);
}
try
{
scrollViewer.ViewChanged += ViewChanged;
switch (scrollToPosition)
{
case ScrollToPosition.MakeVisible:
list.ScrollIntoView(targetItem, ScrollIntoViewAlignment.Default);
break;
case ScrollToPosition.Start:
list.ScrollIntoView(targetItem, ScrollIntoViewAlignment.Leading);
break;
case ScrollToPosition.Center:
list.ScrollIntoView(targetItem, ScrollIntoViewAlignment.Leading);
adjust = () => AdjustToCenterAsync(list, scrollViewer, targetItem);
break;
case ScrollToPosition.End:
list.ScrollIntoView(targetItem, ScrollIntoViewAlignment.Leading);
adjust = () => AdjustToEndAsync(list, scrollViewer, targetItem);
break;
}
await tcs.Task;
}
finally
{
scrollViewer.ViewChanged -= ViewChanged;
}
}
async Task AnimateTo(ListViewBase list, object targetItem, ScrollToPosition scrollToPosition)
{
var scrollViewer = list.GetFirstDescendant <ScrollViewer>();
var targetContainer = list.ContainerFromItem(targetItem) as UIElement;
if (targetContainer == null)
{
var horizontalOffset = scrollViewer.HorizontalOffset;
var verticalOffset = scrollViewer.VerticalOffset;
await JumpTo(list, targetItem, scrollToPosition);
targetContainer = list.ContainerFromItem(targetItem) as UIElement;
await ChangeViewAsync(scrollViewer, horizontalOffset, verticalOffset, true);
}
if (targetContainer == null)
{
// Did not find the target item anywhere
return;
}
// TODO hartez 2018/10/04 16:37:35 Okay, this sort of works for vertical lists but fails totally on horizontal lists.
var transform = targetContainer.TransformToVisual(scrollViewer.Content as UIElement);
var position = transform?.TransformPoint(new Windows.Foundation.Point(0, 0));
if (!position.HasValue)
{
return;
}
// TODO hartez 2018/10/05 17:23:23 The animated scroll works fine vertically if we are scrolling to a greater Y offset.
// If we're scrolling back up to a lower Y offset, it just gives up and sends us to 0 (first item)
// Works fine if we disable animation, but that's not very helpful
scrollViewer.ChangeView(position.Value.X, position.Value.Y, null, false);
//if (scrollToPosition == ScrollToPosition.End)
//{
// // Modify position
//}
//else if (scrollToPosition == ScrollToPosition.Center)
//{
// // Modify position
//}
//else
//{
//}
}
internal static void JumpToIndexAsync(ListViewBase list, int index, ScrollToPosition scrollToPosition)
{
var scrollViewer = list.GetFirstDescendant <ScrollViewer>();
var con = list.ContainerFromIndex(index);
if (con is UIElement uIElement)
{
var width = uIElement.DesiredSize.Width;
var current = scrollViewer.HorizontalOffset;
var delta = (index * width) - current;
scrollViewer.ChangeView(current + delta, scrollViewer.VerticalOffset, scrollViewer.ZoomFactor, true);
}
}
public static (int firstVisibleItemIndex, int lastVisibleItemIndex, int centerItemIndex) GetVisibleIndexes(this ListViewBase listViewBase, ItemsLayoutOrientation itemsLayoutOrientation, bool goingNext)
{
int firstVisibleItemIndex = -1;
int lastVisibleItemIndex = -1;
var itemsPanel = (listViewBase.ItemsPanelRoot as ItemsStackPanel);
if (itemsPanel != null)
{
firstVisibleItemIndex = itemsPanel.FirstVisibleIndex;
lastVisibleItemIndex = itemsPanel.LastVisibleIndex;
}
else
{
var scrollViewer = listViewBase.GetFirstDescendant <ScrollViewer>();
var presenters = listViewBase.GetChildren <ListViewItemPresenter>();
if (presenters != null || scrollViewer == null)
{
int count = 0;
foreach (ListViewItemPresenter presenter in presenters)
{
if (IsListViewItemVisible(presenter, scrollViewer, itemsLayoutOrientation))
{
if (firstVisibleItemIndex == -1)
{
firstVisibleItemIndex = count;
}
lastVisibleItemIndex = count;
}
count++;
}
}
}
double center = (lastVisibleItemIndex + firstVisibleItemIndex) / 2.0;
int centerItemIndex = goingNext ? (int)Math.Ceiling(center) : (int)Math.Floor(center);
return(firstVisibleItemIndex, lastVisibleItemIndex, centerItemIndex);
}
void FindScrollViewer(ListViewBase listView)
{
var scrollViewer = listView.GetFirstDescendant <ScrollViewer>();
if (scrollViewer != null)
{
OnScrollViewerFound(scrollViewer);
return;
}
void ListViewLoaded(object sender, RoutedEventArgs e)
{
var lv = (ListViewBase)sender;
lv.Loaded -= ListViewLoaded;
FindScrollViewer(listView);
}
listView.Loaded += ListViewLoaded;
}
protected virtual void FindScrollViewer(ListViewBase listView)
{
var scrollViewer = listView.GetFirstDescendant <ScrollViewer>();
if (scrollViewer != null)
{
_scrollViewer = scrollViewer;
_scrollViewer.ViewChanged += OnScrollViewChanged;
return;
}
void ListViewLoaded(object sender, RoutedEventArgs e)
{
var lv = (ListViewBase)sender;
lv.Loaded -= ListViewLoaded;
FindScrollViewer(listView);
}
listView.Loaded += ListViewLoaded;
}
void OnListSizeChanged(object sender, Windows.UI.Xaml.SizeChangedEventArgs e)
{
var newSize = e.NewSize;
_carouselHeight = newSize.Height;
_carouselWidth = newSize.Width;
_scrollViewer = ListViewBase.GetFirstDescendant <ScrollViewer>();
if (_scrollViewer != null)
{
// TODO: jsuarezruiz This breaks the ScrollTo override. Review it.
_scrollViewer.ViewChanging += OnScrollViewChanging;
_scrollViewer.ViewChanged += OnScrollViewChanged;
}
UpdateItemsSource();
UpdateItemTemplate();
UpdateIsSwipeEnabled();
UpdateIsBounceEnabled();
}
protected override void FindScrollViewer(ListViewBase listView)
{
var scrollViewer = listView.GetFirstDescendant <ScrollViewer>();
if (scrollViewer != null)
{
_scrollViewer = scrollViewer;
// TODO: jsuarezruiz This breaks the ScrollTo override. Review it.
_scrollViewer.ViewChanging += OnScrollViewChanging;
_scrollViewer.ViewChanged += OnScrollViewChanged;
return;
}
void ListViewLoaded(object sender, Windows.UI.Xaml.RoutedEventArgs e)
{
var lv = (ListViewBase)sender;
lv.Loaded -= ListViewLoaded;
FindScrollViewer(listView);
}
listView.Loaded += ListViewLoaded;
}
