Make ListView.ScrollIntoView Scroll the Item into the Center of the ListView (C#)
C#WpfVisual StudioListviewC# Problem Overview
ListView.ScrollIntoView(object)
currently finds an object in the ListView
and scrolls to it. If you are positioned beneath the object you are scrolling to, it scrolls the object to the top row. If you are positioned above, it scrolls it into view at the bottom row.
I'd like to have the item be scrolled right into the center of my list view if it is currently not visible. Is there an easy way to accomplish this?
C# Solutions
Solution 1 - C#
It is very easy to do this in WPF with an extension method I wrote. All you have to do to scroll an item to the center of the view is to call a single method.
Suppose you have this XAML:
<ListView x:Name="view" ItemsSource="{Binding Data}" />
<ComboBox x:Name="box" ItemsSource="{Binding Data}"
SelectionChanged="ScrollIntoView" />
Your ScrollIntoView method will be simply:
private void ScrollIntoView(object sender, SelectionChangedEventArgs e)
{
view.ScrollToCenterOfView(box.SelectedItem);
}
Obviously this could be done using a ViewModel as well rather than referencing the controls explicitly.
Following is the implementation. It is very general, handling all the IScrollInfo possibilities. It works with ListBox or any other ItemsControl, and works with any panel including StackPanel, VirtualizingStackPanel, WrapPanel, DockPanel, Canvas, Grid, etc.
Just put this in a .cs file somewhere in your project:
public static class ItemsControlExtensions
{
public static void ScrollToCenterOfView(this ItemsControl itemsControl, object item)
{
// Scroll immediately if possible
if(!itemsControl.TryScrollToCenterOfView(item))
{
// Otherwise wait until everything is loaded, then scroll
if(itemsControl is ListBox) ((ListBox)itemsControl).ScrollIntoView(item);
itemsControl.Dispatcher.BeginInvoke(DispatcherPriority.Loaded, new Action(() =>
{
itemsControl.TryScrollToCenterOfView(item);
}));
}
}
private static bool TryScrollToCenterOfView(this ItemsControl itemsControl, object item)
{
// Find the container
var container = itemsControl.ItemContainerGenerator.ContainerFromItem(item) as UIElement;
if(container==null) return false;
// Find the ScrollContentPresenter
ScrollContentPresenter presenter = null;
for(Visual vis = container; vis!=null && vis!=itemsControl; vis = VisualTreeHelper.GetParent(vis) as Visual)
if((presenter = vis as ScrollContentPresenter)!=null)
break;
if(presenter==null) return false;
// Find the IScrollInfo
var scrollInfo =
!presenter.CanContentScroll ? presenter :
presenter.Content as IScrollInfo ??
FirstVisualChild(presenter.Content as ItemsPresenter) as IScrollInfo ??
presenter;
// Compute the center point of the container relative to the scrollInfo
Size size = container.RenderSize;
Point center = container.TransformToAncestor((Visual)scrollInfo).Transform(new Point(size.Width/2, size.Height/2));
center.Y += scrollInfo.VerticalOffset;
center.X += scrollInfo.HorizontalOffset;
// Adjust for logical scrolling
if(scrollInfo is StackPanel || scrollInfo is VirtualizingStackPanel)
{
double logicalCenter = itemsControl.ItemContainerGenerator.IndexFromContainer(container) + 0.5;
Orientation orientation = scrollInfo is StackPanel ? ((StackPanel)scrollInfo).Orientation : ((VirtualizingStackPanel)scrollInfo).Orientation;
if(orientation==Orientation.Horizontal)
center.X = logicalCenter;
else
center.Y = logicalCenter;
}
// Scroll the center of the container to the center of the viewport
if(scrollInfo.CanVerticallyScroll) scrollInfo.SetVerticalOffset(CenteringOffset(center.Y, scrollInfo.ViewportHeight, scrollInfo.ExtentHeight));
if(scrollInfo.CanHorizontallyScroll) scrollInfo.SetHorizontalOffset(CenteringOffset(center.X, scrollInfo.ViewportWidth, scrollInfo.ExtentWidth));
return true;
}
private static double CenteringOffset(double center, double viewport, double extent)
{
return Math.Min(extent - viewport, Math.Max(0, center - viewport/2));
}
private static DependencyObject FirstVisualChild(Visual visual)
{
if(visual==null) return null;
if(VisualTreeHelper.GetChildrenCount(visual)==0) return null;
return VisualTreeHelper.GetChild(visual, 0);
}
}
Solution 2 - C#
Ray Burns' excellent answer above is WPF specific.
Here is a modified version that works in Silverlight:
public static class ItemsControlExtensions
{
public static void ScrollToCenterOfView(this ItemsControl itemsControl, object item)
{
// Scroll immediately if possible
if (!itemsControl.TryScrollToCenterOfView(item))
{
// Otherwise wait until everything is loaded, then scroll
if (itemsControl is ListBox) ((ListBox)itemsControl).ScrollIntoView(item);
itemsControl.Dispatcher.BeginInvoke( new Action(() =>
{
itemsControl.TryScrollToCenterOfView(item);
}));
}
}
private static bool TryScrollToCenterOfView(this ItemsControl itemsControl, object item)
{
// Find the container
var container = itemsControl.ItemContainerGenerator.ContainerFromItem(item) as UIElement;
if (container == null) return false;
// Find the ScrollContentPresenter
ScrollContentPresenter presenter = null;
for (UIElement vis = container; vis != null ; vis = VisualTreeHelper.GetParent(vis) as UIElement)
if ((presenter = vis as ScrollContentPresenter) != null)
break;
if (presenter == null) return false;
// Find the IScrollInfo
var scrollInfo =
!presenter.CanVerticallyScroll ? presenter :
presenter.Content as IScrollInfo ??
FirstVisualChild(presenter.Content as ItemsPresenter) as IScrollInfo ??
presenter;
// Compute the center point of the container relative to the scrollInfo
Size size = container.RenderSize;
Point center = container.TransformToVisual((UIElement)scrollInfo).Transform(new Point(size.Width / 2, size.Height / 2));
center.Y += scrollInfo.VerticalOffset;
center.X += scrollInfo.HorizontalOffset;
// Adjust for logical scrolling
if (scrollInfo is StackPanel || scrollInfo is VirtualizingStackPanel)
{
double logicalCenter = itemsControl.ItemContainerGenerator.IndexFromContainer(container) + 0.5;
Orientation orientation = scrollInfo is StackPanel ? ((StackPanel)scrollInfo).Orientation : ((VirtualizingStackPanel)scrollInfo).Orientation;
if (orientation == Orientation.Horizontal)
center.X = logicalCenter;
else
center.Y = logicalCenter;
}
// Scroll the center of the container to the center of the viewport
if (scrollInfo.CanVerticallyScroll) scrollInfo.SetVerticalOffset(CenteringOffset(center.Y, scrollInfo.ViewportHeight, scrollInfo.ExtentHeight));
if (scrollInfo.CanHorizontallyScroll) scrollInfo.SetHorizontalOffset(CenteringOffset(center.X, scrollInfo.ViewportWidth, scrollInfo.ExtentWidth));
return true;
}
private static double CenteringOffset(double center, double viewport, double extent)
{
return Math.Min(extent - viewport, Math.Max(0, center - viewport / 2));
}
private static DependencyObject FirstVisualChild(UIElement visual)
{
if (visual == null) return null;
if (VisualTreeHelper.GetChildrenCount(visual) == 0) return null;
return VisualTreeHelper.GetChild(visual, 0);
}
}
Solution 3 - C#
Ray Burns' excellent answer above and the comment from Fyodor Soikin:
"Actually, it doesn't work with any other ItemsControl... doesn't work with DataGrid with virtualization turned on..."
Use:
if (listBox.SelectedItem != null)
{
listBox.ScrollIntoView(listBox.SelectedItem);
listBox.ScrollToCenterOfView(listBox.SelectedItem);
}
@all: cant comment at the moment, need 50 reputation
Solution 4 - C#
I seem to recall doing something like this myself at some point. As far as my memory goes, what I did was:
- Determine if the object is already visible or not.
- If it's not visible, get the index of the object you want, and the number of objects currently displayed.
(index you want) - (number of objects displayed / 2)
should be the top row, so scroll to that (making sure you don't go negative, of course)
Solution 5 - C#
If you look at the template of a Listbox it is simply a scrollviewer with an itemspresenter inside. You'll need to calculate the size of your items and use scroll horizontally or vertically to position the items in your scrollviewer. The april silverlight toolkit has an extension method GetScrollHost that you can call on a listbox to get your underlying scrollviewer.
Once you have that you can use the current Horizontal or Vertical Offset as a frame of reference and move your list accordinly.
Solution 6 - C#
The below sample will find the scrollviewer of the listview and use it to scroll the item to me middle of the listview.
XAML:
<Window x:Class="ScrollIntoViewTest.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Height="300" Width="300">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="*" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<ListView Grid.Row="0" ItemsSource="{Binding Path=Data}" Loaded="OnListViewLoaded"/>
<ComboBox Grid.Row="1" ItemsSource="{Binding Path=Data}" SelectionChanged="OnScrollIntoView" />
</Grid>
</Window>
Code behind:
using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
namespace ScrollIntoViewTest
{
public partial class Window1 : Window
{
public Window1()
{
InitializeComponent();
Data = new List<string>();
for (int i = 0; i < 100; i++)
{
Data.Add(i.ToString());
}
DataContext = this;
}
public List<string> Data { get; set; }
private void OnListViewLoaded(object sender, RoutedEventArgs e)
{
// Assumes that the listview consists of a scrollviewer with a border around it
// which is the default.
Border border = VisualTreeHelper.GetChild(sender as DependencyObject, 0) as Border;
_scrollViewer = VisualTreeHelper.GetChild(border, 0) as ScrollViewer;
}
private void OnScrollIntoView(object sender, SelectionChangedEventArgs e)
{
string item = (sender as ComboBox).SelectedItem as string;
double index = Data.IndexOf(item) - Math.Truncate(_scrollViewer.ViewportHeight / 2);
_scrollViewer.ScrollToVerticalOffset(index);
}
private ScrollViewer _scrollViewer;
}
}
Solution 7 - C#
I found an additional approach to solve this problem, assuming some of us just need a way to find out the Height of the visual item according to the item template this would greatly save you time.
Ok, I assume your XAML is structured somehow similiar to this:
:
<Window.Resources>
<DataTemplate x:Key="myTemplate">
<UserControls1:myControl DataContext="{Binding}" />
</DataTemplate>
</Window.Resources>
:
<ListBox Name="myListBox" ItemTemplate="{StaticResource ResourceKey=myTemplate}" />
And you want to calculate in order to scroll to the center but you have no idea what is the current height of each item in your listbox.. this is how you can find out:
listBoxItemHeight = (double)((DataTemplate)FindResource("myTemplate")).LoadContent().GetValue(HeightProperty);
Solution 8 - C#
If the issue is the scroll inconsistency (the difference between scrolling from above / below), this can be solved by first scrolling to the top of the list, and then scrolling to the desired row + half the visible row count. An additional range check will be required to avoid an IndexOutOfRange.
// we add +1 to row height for grid width
var offset = (int)(mDataGrid.RenderSize.Height / (mDataGrid.MinRowHeight + 1) / 2);
// index is the item's index in the list
if (index + offset >= mDataGrid.Items.Count) offset = 0;
mDataGrid.ScrollIntoView(mDataGrid.Items[0]);
mDataGrid.ScrollIntoView(mDataGrid.Items[index + offsest]);
Solution 9 - C#
I know this post is old but I wanted to provide the UWP version of Ray Burns' excellent answer above
public static async void ScrollToCenterOfView(this ItemsControl itemsControl, object item)
{
// Scroll immediately if possible
if (!itemsControl.TryScrollToCenterOfView(item))
{
// Otherwise wait until everything is loaded, then scroll
if (itemsControl is ListBox) ((ListBox)itemsControl).ScrollIntoView(item);
await itemsControl.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
itemsControl.TryScrollToCenterOfView(item);
});
}
}
private static bool TryScrollToCenterOfView(this ItemsControl itemsControl, object item)
{
// Find the container
var container = itemsControl.ContainerFromItem(item) as FrameworkElement;
if (container == null) return false;
var scrollPresenter = container.FindParent(typeof(ScrollContentPresenter)) as ScrollContentPresenter;
if (scrollPresenter == null) return false;
Size size = container.RenderSize;
var center = container.TransformToVisual(scrollPresenter).TransformPoint(new Point(size.Width / 2, size.Height / 2));
center.Y += scrollPresenter.VerticalOffset;
center.X += scrollPresenter.HorizontalOffset;
// Scroll the center of the container to the center of the viewport
if (scrollPresenter.CanVerticallyScroll) scrollPresenter.SetVerticalOffset(CenteringOffset(center.Y, scrollPresenter.ViewportHeight, scrollPresenter.ExtentHeight));
if (scrollPresenter.CanHorizontallyScroll) scrollPresenter.SetHorizontalOffset(CenteringOffset(center.X, scrollPresenter.ViewportWidth, scrollPresenter.ExtentWidth));
return true;
}
public static FrameworkElement FindParent(this FrameworkElement o, Type type)
{
for (var element = VisualTreeHelper.GetParent(o) as FrameworkElement;
element != null;
element = VisualTreeHelper.GetParent(element) as FrameworkElement)
{
if (element?.GetType() == type) return element;
}
return null;
}
private static double CenteringOffset(double center, double viewport, double extent)
{
return Math.Min(extent - viewport, Math.Max(0, center - viewport / 2));
}