private void PhotosPage_Loaded(object sender, RoutedEventArgs args) { //var scrollViewer = ItemsGridView.GetScrollViewer(); //if (scrollViewer == null) return; //scrollViewer.LayoutUpdated += (s, _) => //{ // Debug.WriteLine(scrollViewer.VerticalOffset); // //scrollViewer.ScrollableHeight == scrollViewer.VerticalOffset //到底 //}; //return; var scrollViewer = ItemsGridView.FindDescendant <ScrollViewer>(); var scrollbars = scrollViewer.GetDescendantsOfType <ScrollBar>().ToList(); var verticalBar = scrollbars.FirstOrDefault(x => x.Orientation == Orientation.Vertical); scrollViewer.ViewChanged += (_, e) => { if (e.IsIntermediate) { return; } TopAppBarButton.Visibility = scrollViewer.VerticalOffset == 0 ? Visibility.Collapsed : Visibility.Visible; }; TopAppBarButton.Click += (s, e) => { scrollViewer.ChangeView(null, 0, null, false); }; RefreshAppBarButton.Click += AppBarButton_Click; }