Retrieve XAML control from code behind

VisualTreeExtension.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Windows.Foundation;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Media;

namespace appNamespace.Helpers {
    public static class VisualTreeExtensions {
        public static T GetChildOfType<T>(this DependencyObject depObj) where T : DependencyObject {
            if (depObj == null) return null;

            for (int i = 0; i < VisualTreeHelper.GetChildrenCount(depObj); i++) {
                var child = VisualTreeHelper.GetChild(depObj, i);

                var result = (child as T) ?? GetChildOfType<T>(child);
                if (result != null) return result;
            }
            return null;
        }

        public static T GetParentOfType<T>(this DependencyObject depObj) where T : DependencyObject {
            if (depObj == null) return null;

            var parent = VisualTreeHelper.GetParent(depObj);

            var result = (parent as T) ?? GetParentOfType<T>(parent);
            if (result != null) return result;
            return null;
        }

        public async static Task ScrollToIndex(this ListViewBase listViewBase, int index) {
            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.ContainerFromIndex(index) 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(listViewBase.Items[index]);

                // this time the item shouldn't be null again
                selectorItem = (SelectorItem)listViewBase.ContainerFromIndex(index);
            }

            // 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);
        }

        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);
        }

        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 static async Task ChangeViewAsync(this ScrollViewer scrollViewer, double? horizontalOffset, double? verticalOffset, bool disableAnimation) {
            var tcs = new TaskCompletionSource<object>();

            EventHandler<ScrollViewerViewChangedEventArgs> viewChanged = (s, e) => tcs.TrySetResult(null);
            try {
                scrollViewer.ViewChanged += viewChanged;
                scrollViewer.ChangeView(horizontalOffset, verticalOffset, null, disableAnimation);
                await tcs.Task;
            }
            finally {
                scrollViewer.ViewChanged -= viewChanged;
            }
        }

    }
}