ListBox – Automatically scroll to bottom
In WinForms it was so simple to tell the ListBox to scroll to the buttom.
But in WPF it seems to be rather difficult but it is not.
You can simply create an attached property and once done it will do it for you.
Simply add the attached property to your ListBox
<ListBox ItemsSource="{....}" Extenders:ListBoxExtenders.AutoScrollToEnd="True" />
And here is the source code of the attached property
/// <summary>
/// This class contains a few useful extenders for the ListBox
/// </summary>
public class ListBoxExtenders : DependencyObject
{
public static readonly DependencyProperty AutoScrollToEndProperty = DependencyProperty.RegisterAttached("AutoScrollToEnd", typeof(bool), typeof(ListBoxExtenders), new UIPropertyMetadata(default(bool), OnAutoScrollToEndChanged));
/// <summary>
/// Returns the value of the AutoScrollToEndProperty
/// </summary>
/// <param name="obj">The dependency-object whichs value should be returned</param>
/// <returns>The value of the given property</returns>
public static bool GetAutoScrollToEnd(DependencyObject obj)
{
return (bool)obj.GetValue(AutoScrollToEndProperty);
}
/// <summary>
/// Sets the value of the AutoScrollToEndProperty
/// </summary>
/// <param name="obj">The dependency-object whichs value should be set</param>
/// <param name="value">The value which should be assigned to the AutoScrollToEndProperty</param>
public static void SetAutoScrollToEnd(DependencyObject obj, bool value)
{
obj.SetValue(AutoScrollToEndProperty, value);
}
/// <summary>
/// This method will be called when the AutoScrollToEnd
/// property was changed
/// </summary>
/// <param name="s">The sender (the ListBox)</param>
/// <param name="e">Some additional information</param>
public static void OnAutoScrollToEndChanged(DependencyObject s, DependencyPropertyChangedEventArgs e)
{
var listBox = s as ListBox;
var listBoxItems = listBox.Items;
var data = listBoxItems.SourceCollection as INotifyCollectionChanged;
var scrollToEndHandler = new System.Collections.Specialized.NotifyCollectionChangedEventHandler(
(s1, e1) =>
{
if (listBox.Items.Count > 0)
{
object lastItem = listBox.Items[listBox.Items.Count - 1];
listBoxItems.MoveCurrentTo(lastItem);
listBox.ScrollIntoView(lastItem);
}
});
if ((bool)e.NewValue)
data.CollectionChanged += scrollToEndHandler;
else
data.CollectionChanged -= scrollToEndHandler;
}
}
Note that it is similar to the scroll current element into view
So check this out: scroll current item into view
michlG's Blog 
Used with a listbox, with itemssource databinding, it doesn’t work.
Replace OnAutoScrollToEndChanged by OnIsAutoscrollChanged method to fix it @ http://khason.net/blog/auto-scroll-listbox-in-wpf/
Hey. Thank you for telling me that.
Now I changed my code a little bit and it works 🙂
I guess that I have not been testing the old code before posting it 😉
The line
data.CollectionChanged -= scrollToEndHandler
potentially leaks memory.
Unregistering events with lambda expressions hs problems, see
http://stackoverflow.com/questions/2465040/using-lambda-expressions-
for-event-handlers/2465054#2465054
Hi, thanks for the information. I will fix that when I find a bit of time 🙂
I tried this and yes the lamba expression does not unregister correctly because you are not using the exact same lamba. You are simply declaring another one that looks the same. And you can’t store the original one because you are working inside a static function.
However I did find a workaround. Since the same ListBox is injected into the OnAutoScrollToEndChanged() method we can store the exact EventHandler there by using the ListBox’s Tag property:
if ((bool)e.NewValue)
{
if (listBox.Tag == null)
data.CollectionChanged += scrollToEndHandler;
listBox.Tag = scrollToEndHandler;
}
else
{
var eventHandler = listBox.Tag as NotifyCollectionChangedEventHandler;
if (listBox.Tag != null && eventHandler != null)
data.CollectionChanged -= (NotifyCollectionChangedEventHandler)listBox.Tag;
listBox.Tag = scrollToEndHandler;
}
Thanks for sharing this. It works like charm.
Databind the AutoScrollToEnd to property on view model.
I set the property if any item is selected it will not scroll
And changed from ListBox to ListView for my own purposes.
Added:
private static Dictionary eventPointer = new Dictionary();
then changed OnAutoScrollToEndChanged to:
public static void OnAutoScrollToEndChanged(DependencyObject s, DependencyPropertyChangedEventArgs e)
{
var listView = s as ListView;
var listViewItems = listView.Items;
var data = listViewItems.SourceCollection as INotifyCollectionChanged;
if ((bool)e.NewValue)
{
var scrollToEndHandler = new System.Collections.Specialized.NotifyCollectionChangedEventHandler(
(s1, e1) =>
{
if (listView.Items.Count > 0)
{
object lastItem = listView.Items[listView.Items.Count – 1];
listViewItems.MoveCurrentTo(lastItem);
listView.ScrollIntoView(lastItem);
}
});
eventPointer[listView] = scrollToEndHandler;
data.CollectionChanged += scrollToEndHandler;
}
else if (eventPointer.ContainsKey(listView))
{
data.CollectionChanged -= eventPointer[listView];
eventPointer.Remove(listView);
}
}
Works like a charm – you made ma day !!! Thank you so much.