WPF - How to add onScroll Event to ListBox and Access the ScrollViewer

Question

I define my ListBox like this in XAML:

<ListBox Name="myListBox" 
         HorizontalContentAlignment="Stretch" 
         ScrollViewer.HorizontalScrollBarVisibility="Hidden" 
         ScrollViewer.ScrollChanged="OnScrollChanged" <- I want to create onScrollChanged event
         Grid.Row="0">
         ...
</ListBox>

Then in my cs file, I define this event:

private void OnScrollChanged(object sender, ScrollChangedEventArgs e)
{

    var scrollViewer = (ScrollViewer)sender; //ERROR
    if (scrollViewer.VerticalOffset == scrollViewer.ScrollableHeight)
        MessageBox.Show("This is the end");
}

I am trying to detect when user scrolls to the very bottom of ListBox. But I get error that ListBox cannot be casted to Scrollviewer. How do I get the scrollviewer?

Thanks

score 1 · Accepted Answer · answered Dec 25 '15 at 03:55

1

Add a ScrollViewer around your ListBox in the XAML, and subscribe to the event from there.

<ScrollViewer ScrollChanged="OnScrollChanged">
    <ListBox Name="myListBox" 
             HorizontalContentAlignment="Stretch"
             ScrollViewer.HorizontalScrollBarVisibility="Hidden"
             Grid.Row="0" />
</ScrollViewer>

The code-behind can remain the same.

In your current code, you're trying to convert your ListBox (the "sender") to a ScrollViewer, which it cannot do, so it throws an exception.

answered Dec 25 '15 at 03:55

Grant Winney

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Thanks Grant but in that case scrollviewer will always show even if Listbox is empty and it will show "This is the end" message which is what I do not want. I load this list dynamically with data, so no message should show if ListBox is empty, only once data is loaded and user scrolls to the bottom. Then I will load more data, that is why I need to detect when scroll bar of my ListBox is scrolled to the end. – pixel Dec 25 '15 at 04:04
That is it. Just using myListBox.Items.Count() instead of Any(). Thanks Grant, Merry X-mass – pixel Dec 25 '15 at 04:51

score 0 · Answer 2 · answered Jan 04 '23 at 09:56

    private void OnScrollChanged(object sender, ScrollChangedEventArgs e)
    {
        // Get the border of the listview (first child of a listview)
        var border = VisualTreeHelper.GetChild(sender as ListView, 0) as Decorator;

        // Get scrollviewer
        var scrollViewer = border.Child as ScrollViewer;

        if (scrollViewer.VerticalOffset == scrollViewer.ScrollableHeight)
        {
            //Write your code here.
        }
    }

WPF - How to add onScroll Event to ListBox and Access the ScrollViewer

2 Answers2