How to get the current item in view for Semantic Zoom control

Question

I am using Semantic Zoom control to show the list of Contacts in my WinRT application. When I manually scroll the list, I want to get the current item which is in view (there will be more than one items in view, but I would like to get the closest one which is in view). So that I can save the scrolling position to set it as it is when user navigates back to this list of contact. Any suggestion? I tried getting the current Selected Index but it never got updated while scrolling through the list:

int lastViewedItem = ((ListViewBase)this.semanticZoom.ZoomedInView).SelectedIndex;

On navigating back

(ListViewBase)this.semanticZoom.ZoomedInView).SelectedIndex = lastViewedItem;

 ((ListViewBase)this.semanticZoom.ZoomedInView).ScrollIntoView(((ListViewBase)this.semanticZoom.ZoomedInView).SelectedItem);

Filip Skakun · Accepted Answer · 2015-02-27T06:34:07.847

I've created an extension to do just for any known ItemsControl that I knew here.

using System;
using System.Collections;
using Windows.Foundation;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;

/// <summary>
/// Gets the first visible element.
/// </summary>
/// <param name="itemsControl">The ItemsControl.</param>
/// <returns>The first visible item or null if not found.</returns>
public static object GetFirstVisibleItem(this ItemsControl itemsControl)
{
    var index = GetFirstVisibleIndex(itemsControl);

    if (index == -1)
    {
        return null;
    }

    var list = itemsControl.ItemsSource as IList;

    if (itemsControl.ItemsSource != null &&
        list != null &&
        list.Count > index)
    {
        return list[index];
    }

    if (itemsControl.Items != null &&
        itemsControl.Items.Count > index)
    {
        return itemsControl.Items[index];
    }

    throw new InvalidOperationException();
}

/// <summary>
/// Gets the index of the first visible element.
/// </summary>
/// <param name="itemsControl">The ItemsControl.</param>
/// <returns>The index of the first visible item or -1 if not found.</returns>
public static int GetFirstVisibleIndex(this ItemsControl itemsControl)
{
    // First checking if no items source or an empty one is used
    if (itemsControl.ItemsSource == null)
    {
        return -1;
    }

    var enumItemsSource = itemsControl.ItemsSource as IEnumerable;

    if (enumItemsSource != null && !enumItemsSource.GetEnumerator().MoveNext())
    {
        return -1;
    }

    // Check if a modern panel is used as an items panel
    var sourcePanel = itemsControl.ItemsPanelRoot;

    if (sourcePanel == null)
    {
        throw new InvalidOperationException("Can't get first visible index from an ItemsControl with no ItemsPanel.");
    }

    var isp = sourcePanel as ItemsStackPanel;

    if (isp != null)
    {
        return isp.FirstVisibleIndex;
    }

    var iwg = sourcePanel as ItemsWrapGrid;

    if (iwg != null)
    {
        return iwg.FirstVisibleIndex;
    }

    // Check containers for first one in view
    if (sourcePanel.Children.Count == 0)
    {
        return -1;
    }

    if (itemsControl.ActualWidth == 0)
    {
        throw new InvalidOperationException("Can't get first visible index from an ItemsControl that is not loaded or has zero size.");
    }

    for (int i = 0; i < sourcePanel.Children.Count; i++)
    {
        var container = (FrameworkElement)sourcePanel.Children[i];
        var bounds = container.TransformToVisual(itemsControl).TransformBounds(new Rect(0, 0, container.ActualWidth, container.ActualHeight));

        if (bounds.Left < itemsControl.ActualWidth &&
            bounds.Top < itemsControl.ActualHeight &&
            bounds.Right > 0 &&
            bounds.Bottom > 0)
        {
            return itemsControl.IndexFromContainer(container);
        }
    }

    throw new InvalidOperationException();
}

You code to get the FirstVisibleItem works awesome. But, when I try and call ScrollIntoView for that item, it doesn't work 20% of the time. I know it's not a part of the discussion in this thread though :) — tavier, Feb 27 '15 at 13:01

How to get the current item in view for Semantic Zoom control

1 Answers1