Scroll ListViewItem to be at the top of a ListView

Question

In WPF, I know I can use ListView.ScrollIntoView to scroll a particular item into view, but it will always do the least amount of scrolling so that the item is shown.

How can I make it scroll so that the item I want to show is scrolled to the top of the ListView?

I've thought about calling ScrollIntoView twice, once for the item I want at the top, and once for the last shown item, but I don't know how to find out what the last shown item.

Hymenium

Answer 1

We can do this by obtaining the ScrollViewer that is present in the ListView's ControlTemplate. If you have access to a ScrollViewer then there are a lot of different scrolling methods exposed.

First, we can create a ListView that we want to add this effect to:

<ListView ItemsSource="{Binding Percents}"
      SelectionChanged="OnSelectionChanged"
      x:Name="uiListView"/>

public List<int> Percents { get; set; }

public Window1()
{
    InitializeComponent();

    Percents = new List<int>();
    for (int i = 1; i <= 100; i++)
    {
        Percents.Add(i);
    }
    this.DataContext = this;
}

We will also need something that we can use to obtain the ScrollViewer from the ListView. I've used something similar to this before to work with custom scrolling, and we can use it here as well.

public static DependencyObject GetScrollViewer(DependencyObject o)
{
    if (o is ScrollViewer)
    { return o; }

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

        var result = GetScrollViewer(child);
        if (result == null)
        {
            continue;
        }
        else
        {
            return result;
        }
    }

    return null;
}

Now, we just need to handle the SelectionChanged event. Because we are trying to scroll an item to the top of the list, the best option is to scroll to the bottom, and then re-scroll up to our selected item. As you said, ScrollIntoView will scroll just until the item is visible, and so once the selected item reaches the top as it scrolls back up, it will cease leaving us with our selected item at the very top of the list.

private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
{
    ScrollViewer scrollViewer = GetScrollViewer(uiListView) as ScrollViewer;
    scrollViewer.ScrollToBottom();

    uiListView.ScrollIntoView(e.AddedItems[0]);
}

Labannah

Note, if you are using the WPF Extended Toolkit, you can get the ScrollViewer in one line of code: VisualTreeHelperEx.FindDescendantByType<ScrollViewer>(YourListView); – Branle

Nice @Mr.Bungle! Just adding a little: VisualTreeHelperEx is in Xceed.Wpf.Toolkit.Core.Utilities namespace. Had to dig a little to find it that deep ;-) – Kilocycle

Answer 2

This is an alternative to the answer of @rmoore that avoids scrolling to the bottom. Also note that this is only usefull in cases where SelectionMode=Single.

In case that ScrollViewer.CanContentScroll=True the ScrollViewer can scroll directly to the SelectedIndex.

private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
{
    ScrollViewer scrollViewer = GetScrollViewer(uiListView) as ScrollViewer;      
    scrollViewer.ScrollToVerticalOffset(listView.SelectedIndex);
}

and in case ScrollViewer.CanContentScroll=False some additional XAML is required:

<ListView ScrollViewer.CanContentScroll="False" ItemsSource="{Binding Percents}" x:Name="uiListView">
    <ListView.ItemContainerStyle>
        <Style TargetType="{x:Type ListViewItem}">
            <EventSetter Event="Selected" Handler="OnSelected"/>
        </Style>
     </ListView.ItemContainerStyle>
</ListView>

And the ScrollViewer can move to the vertical offset of the top of the ListViewItem.

private void OnSelected(object sender, RoutedEventArgs e)
{
    ScrollViewer scrollViewer = GetScrollViewer(uiListView) as ScrollViewer;      

    ListViewItem listViewItem = (ListViewItem)e.Source;
    Point offset = listViewItem.TranslatePoint(new Point(), scrollViewer);
    scrollViewer.ScrollToVerticalOffset(scrollViewer.VerticalOffset + offset.Y);
}

Kimberli

Note that ScrollViewer.CanContentScroll="False" disables virtualization. – Hermitage