public static async Task ScrollToItem(this ScrollViewer scrollViewer, SelectorItem selectorItem)
{
// 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(-scrollViewer.ViewportWidth / 2.0, 0));
// touch selection works without animation so the workaround is needed
await Task.Delay(1);
scrollViewer.ChangeView(position.X, position.Y, null);
}
private static async Task ScrollIntoView(
ListViewBase listViewBase,
ScrollViewer scrollViewer,
SelectorItem selectorItem,
bool isVirtualizing,
double previousXOffset,
double previousYOffset,
ItemPosition itemPosition = ItemPosition.Default,
bool disableAnimation = false)
{
var transform = selectorItem.TransformToVisual((UIElement)scrollViewer.Content);
var position = transform.TransformPoint(new Point(0, 0));
if (isVirtualizing)
{
var tcs = new TaskCompletionSource <object>();
EventHandler <ScrollViewerViewChangedEventArgs> viewChanged = (s, e) => tcs.TrySetResult(null);
try
{
scrollViewer.ViewChanged += viewChanged;
scrollViewer.ChangeView(previousXOffset, previousYOffset, null, true);
await tcs.Task;
}
finally
{
scrollViewer.ViewChanged -= viewChanged;
}
}
var listViewBaseWidth = listViewBase.ActualWidth;
var selectorItemWidth = selectorItem.ActualWidth;
var listViewBaseHeight = listViewBase.ActualHeight;
var selectorItemHeight = selectorItem.ActualHeight;
previousXOffset = scrollViewer.HorizontalOffset;
previousYOffset = scrollViewer.VerticalOffset;
if (itemPosition == ItemPosition.Left)
{
scrollViewer.ChangeView(position.X, previousYOffset, null, disableAnimation);
}
else if (itemPosition == ItemPosition.Top)
{
scrollViewer.ChangeView(previousXOffset, position.Y, null, disableAnimation);
}
else if (itemPosition == ItemPosition.Center)
{
var CentreX = (listViewBaseWidth - selectorItemWidth) / 2.0;
var CentreY = (listViewBaseHeight - selectorItemHeight) / 2.0;
var finalXPosition = position.X - CentreX;
var finalYPosition = position.Y - CentreY;
scrollViewer.ChangeView(finalXPosition, finalYPosition, null, disableAnimation);
}
else if (itemPosition == ItemPosition.Right)
{
var finalXPosition = position.X - listViewBaseWidth + selectorItemWidth;
scrollViewer.ChangeView(finalXPosition, previousYOffset, null, disableAnimation);
}
else if (itemPosition == ItemPosition.Bottom)
{
var finalYPosition = position.Y - listViewBaseHeight + selectorItemHeight;
scrollViewer.ChangeView(previousXOffset, finalYPosition, null, disableAnimation);
}
else if (itemPosition == ItemPosition.Default)
{
var bottomXPosition = position.X - listViewBaseWidth + selectorItemWidth;
var finalXPosition = position.X;
if (previousXOffset < position.X && previousXOffset > bottomXPosition)
{
finalXPosition = previousXOffset;
}
else if (Math.Abs(previousXOffset - bottomXPosition) < Math.Abs(previousXOffset - position.X))
{
finalXPosition = bottomXPosition;
}
var rightYPosition = position.Y - listViewBaseHeight + selectorItemHeight;
var finalYPosition = position.Y;
if (previousYOffset < position.Y && previousYOffset > rightYPosition)
{
finalYPosition = previousYOffset;
}
else if (Math.Abs(previousYOffset - rightYPosition) < Math.Abs(previousYOffset - position.Y))
{
finalYPosition = rightYPosition;
}
scrollViewer.ChangeView(finalXPosition, finalYPosition, null, disableAnimation);
}
}
