Centering selected item in a scroll viewer
Solution 1
Try ListView.ScrollIntoView()
or ListView.MakeVisible
first to scroll the container of the item into view and work around it being possibly virtualized out of the UI. Then use
ListView.ItemContainerGenerator
.
ContainerFromIndex
() to get the container of the item and then the VisualTreeHelper
to get its position relative to the ScrollViewer
. Then scroll the scrollviewer by the calculated offset.
*EDIT - Example positioning logic:
Get the VisualTreeHelperExtensions from WinRT XAML Toolkit to get access to the ScrollViewer
easily with GetFirstDescendantOfType()
extension method that wraps some calls to the VisualTreeHelper
.
XAML
<Page
x:Class="ListViewItemCentering.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:ListViewItemCentering"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d">
<Grid
Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<ListView
x:Name="listView">
<ListView.ItemTemplate>
<DataTemplate>
<Border
Width="400"
Height="100">
<ContentControl
Content="{Binding}"
FontSize="48"
Padding="20,10"/>
</Border>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
<Button
Content="Skip"
Width="200"
Height="100"
HorizontalAlignment="Right"
VerticalAlignment="Bottom"
Click="ButtonBase_OnClick"/>
</Grid>
</Page>
C#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Windows.Foundation;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using WinRTXamlToolkit.Controls.Extensions;
namespace ListViewItemCentering
{
/// <summary>
/// An empty page that can be used on its own or navigated to within a Frame.
/// </summary>
public sealed partial class MainPage : Page
{
private Random random = new Random();
public MainPage()
{
this.InitializeComponent();
this.listView.ItemsSource = Enumerable.Range(1, 1000);
this.listView.SelectionChanged += OnListViewSelectionChanged;
}
private async void OnListViewSelectionChanged(object sender, SelectionChangedEventArgs selectionChangedEventArgs)
{
if (listView.SelectedItem == null)
{
return;
}
var item = listView.SelectedItem;
// Calculations relative to screen or ListView
var listViewItem = (FrameworkElement)listView.ContainerFromItem(item);
if (listViewItem == null)
{
listView.ScrollIntoView(item);
}
while (listViewItem == null)
{
await Task.Delay(1); // wait for scrolling to complete - it takes a moment
listViewItem = (FrameworkElement)listView.ContainerFromItem(item);
}
var topLeft =
listViewItem
.TransformToVisual(listView)
.TransformPoint(new Point()).Y;
var lvih = listViewItem.ActualHeight;
var lvh = listView.ActualHeight;
var desiredTopLeft = (lvh - lvih) / 2.0;
var desiredDelta = topLeft - desiredTopLeft;
// Calculations relative to the ScrollViewer within the ListView
var scrollViewer = listView.GetFirstDescendantOfType<ScrollViewer>();
var currentOffset = scrollViewer.VerticalOffset;
var desiredOffset = currentOffset + desiredDelta;
scrollViewer.ScrollToVerticalOffset(desiredOffset);
// better yet if building for Windows 8.1 to make the scrolling smoother use:
// scrollViewer.ChangeView(null, desiredOffset, null);
}
private async void ButtonBase_OnClick(object sender, RoutedEventArgs e)
{
this.listView.SelectedIndex = random.Next(0, ((IEnumerable<int>)this.listView.ItemsSource).Count());
}
}
}
Solution 2
Yup, this worked for me out of the box with ScrollIntoView
private void CountKeyBoard_NavigationEvent(object sender, Controls.UserControls.NavigationEventArgs e)
{
if (lvInvDetails.SelectedItem != null && lvInvDetails.SelectedIndex != -1)
{
switch (e.Direction)
{
case Controls.UserControls.NavigationEventArgs.DirectionEnum.NEXT:
if (lvInvDetails.SelectedIndex >= (lvInvDetails.Items.Count - 1))
lvInvDetails.SelectedIndex = 0;
else
lvInvDetails.SelectedIndex++;
break;
case Controls.UserControls.NavigationEventArgs.DirectionEnum.PREVIOUS:
if (lvInvDetails.SelectedIndex > 0)
lvInvDetails.SelectedIndex--;
else
lvInvDetails.SelectedIndex = lvInvDetails.Items.Count - 1;
break;
}
lvInvDetails.ScrollIntoView(lvInvDetails.SelectedItem);
}
}
Hady
Updated on June 15, 2022Comments
-
Hady almost 2 years
I am trying to center a selected item in a ListView inside a ScrollViewer and struggling to calculate the vertical offset that I should be setting the ScrollViewer relative to the ListView.
The following links set me on the right track, but because of the limitation of the WinRT API, was not able to use them:
- Make ListView.ScrollIntoView Scroll the Item into the Center of the ListView (C#)
- http://blogs.msdn.com/b/delay/archive/2009/04/19/fewer-gotchas-to-getcha-enhancing-the-scrollintoviewcentered-method-for-wpf-s-listbox.aspx
The desired effect is as follows:
This is a sample setup in my XAML:
<ScrollViewer x:Name="MyScrollViewer"> <ListView x:Name="MyView" VerticalAlignment="Center" SelectionChanged="Selector_OnSelectionChanged"> <ListView.ItemTemplate> <DataTemplate> <Grid Width="80" Height="80" Margin="0"> <TextBlock Text="{Binding}" /> </Grid> </DataTemplate> </ListView.ItemTemplate> <ListView.Items> <x:String>1</x:String> <x:String>2</x:String> <x:String>3</x:String> <x:String>4</x:String> <x:String>5</x:String> <x:String>6</x:String> <x:String>7</x:String> <x:String>8</x:String> <x:String>9</x:String> </ListView.Items> </ListView> </ScrollViewer>
Knowing the index of the selected item, how do I calculate the vertical offset that I can use in my method:
private void Selector_OnSelectionChanged(object sender, SelectionChangedEventArgs e) { double maxVerticalOffset = MyScrollViewer.ExtentHeight - MyScrollViewer.ViewportHeight; int selectedItemIndex = MyView.SelectedIndex; double verticalOffset = ... MyScrollViewer.ChangeView(null, verticalOffset, null); }
-
Hady about 10 yearsAre you able to expand on the logic pertaining to using the
VisualTreeHelper
to position the selected listview item in the middle of the scroll viewer? -
Hady about 10 yearsNo luck with the above logic. Given that its a windows store app, I was able to initially get the listViewItem as follows:
ListViewItem listViewItem = (ListViewItem)listView.ContainerFromItem(listView.SelectedItem);
. However, your calculation which I didn't quite understand its logic is very off from being centered in the middle of the ScrollViewer. Perhaps you can post a tested example? -
Filip Skakun about 10 yearsRight, my desiredDelta was the wrong way round. Let me update with a solution.
-
Hady about 10 yearsFantastic. Your sample worked. I think the key mistake that I was making is that I was wrapping my
ListView
with aScrollViewer
control. I didn't know that theListView
presenter itself contained aScrollViewer
built in that I should be using to map coordinates to and from. -
ceth over 9 years@FilipSkakun, I can not find GetFirstDescendantOfType() for ListView. Why ? Thanks for your help.
-
Filip Skakun over 9 yearsYes, this is an extension method in
VisualTreeHelperExtensions
. You can grab the file or just the method or get the entire toolkit from NuGet. -
yalematta about 9 yearsIf I want to do the same feature on a ListView who has an Horizontal Orientation, what should I change in your code? @FilipSkakun
-
Filip Skakun about 9 yearsProbably Y to X and Height to Width