private void DataGridLoaded(DataGrid dataGrid)
{
if (VisualTreeHelperEx.FindVisualChildren <ScrollViewer>(dataGrid).FirstOrDefault() is ScrollViewer scrollViewer)
{
// N.B this doesn't work well if VerticalScrollBar is used to scroll- works for mouse-wheel.
if (MouseFactor > 1)
{
scrollViewer.ScrollChanged += AssociatedObject_ScrollChanged;
}
scrollViewer
.ScrollChanges()
.Select(a => ScrollViewerOnScrollChanged(scrollViewer, dataGrid, a))
.Where(a => a.HasValue)
.Select(a => a.Value)
.ObserveOnDispatcher()
.Subscribe(a =>
{
var(firstVisible, lastVisible) = a;
FirstIndex = firstVisible;
LastIndex = lastVisible;
Size = (lastVisible - firstVisible) + 1;
});
}
void AssociatedObject_ScrollChanged(object sender, ScrollChangedEventArgs e)
{
if (scrollViewer.VerticalOffset == scrollPosition)
{
return;
}
scrollPosition = scrollViewer.VerticalOffset + e.VerticalChange * MouseFactor;
if (scrollPosition >= scrollViewer.ScrollableHeight)
{
scrollViewer.ScrollToBottom();
}
else
{
scrollViewer.ScrollToVerticalOffset(scrollPosition);
}
}
static (int, int)? ScrollViewerOnScrollChanged(ScrollViewer scrollViewer, DataGrid dataGrid, ScrollChangedEventArgs a)
{
//AssociatedObject_ScrollChanged();
if (VisualTreeHelperEx.FindVisualChildren <ScrollBar>(scrollViewer).Single(s => s.Orientation == Orientation.Vertical) is ScrollBar verticalScrollBar)
{
int totalCount = dataGrid.Items.Count;
var firstVisible = (verticalScrollBar.Value);
var lastVisible = (firstVisible + totalCount - verticalScrollBar.Maximum);
return((int)firstVisible, (int)lastVisible);
// GetVisibibleItems(firstVisible, lastVisible, dataGrid).ToArray();
}
return(null);
//static IEnumerable<object> GetVisibibleItems(int firstVisible, int lastVisible, DataGrid dataGrid)
//{
// for (int i = firstVisible; i <= lastVisible; i++)
// {
// yield return dataGrid.Items[i];
// }
//}
}
