Setting the scrollbar position of a ListBox

问题

Can I programatically set the position of a WPF ListBox's scrollbar? By default, I want it to go in the center.

回答1:

To move the vertical scroll bar in a ListBox do the following:

Name your list box (x:Name="myListBox")
Add Loaded event for the Window (Loaded="Window_Loaded")
Implement Loaded event using method: ScrollToVerticalOffset

Here is a working sample:

XAML:

<Window x:Class="ListBoxScrollPosition.Views.MainView"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  Loaded="Window_Loaded"
  Title="Main Window" Height="100" Width="200">
  <DockPanel>
    <Grid>
      <ListBox x:Name="myListBox">
        <ListBoxItem>Zamboni</ListBoxItem>
        <ListBoxItem>Zamboni</ListBoxItem>
        <ListBoxItem>Zamboni</ListBoxItem>
        <ListBoxItem>Zamboni</ListBoxItem>
        <ListBoxItem>Zamboni</ListBoxItem>
        <ListBoxItem>Zamboni</ListBoxItem>
        <ListBoxItem>Zamboni</ListBoxItem>
        <ListBoxItem>Zamboni</ListBoxItem>
        <ListBoxItem>Zamboni</ListBoxItem>
        <ListBoxItem>Zamboni</ListBoxItem>
        <ListBoxItem>Zamboni</ListBoxItem>
        <ListBoxItem>Zamboni</ListBoxItem>
      </ListBox>
    </Grid>
  </DockPanel>
</Window>

private void Window_Loaded(object sender, RoutedEventArgs e)
{
  // Get the border of the listview (first child of a listview)
  Decorator border = VisualTreeHelper.GetChild(myListBox, 0) as Decorator;
  if (border != null)
  {
    // Get scrollviewer
    ScrollViewer scrollViewer = border.Child as ScrollViewer;
    if (scrollViewer != null)
    {
      // center the Scroll Viewer...
      double center = scrollViewer.ScrollableHeight / 2.0;
      scrollViewer.ScrollToVerticalOffset(center);
    }
  }
}

回答2:

Dim cnt as Integer = myListBox.Items.Count
Dim midPoint as Integer = cnt\2
myListBox.ScrollIntoView(myListBox.Items(midPoint))

myListBox.SelectedIndex = midPoint

It depends on if you want the middle item just shown, or selected.

回答3:

I've just changed a bit code of Zamboni and added position calculation.

var border = VisualTreeHelper.GetChild(list, 0) as Decorator;
if (border == null) return;
var scrollViewer = border.Child as ScrollViewer;
if (scrollViewer == null) return;
scrollViewer.ScrollToVerticalOffset((scrollViewer.ScrollableHeight/list.Items.Count)*
                                    (list.Items.IndexOf(list.SelectedItem) + 1));

回答4:

I have a ListView named MusicList. MusicList automatically moves to the next element after playing a music. I create an event handler for Player.Ended event as follows (a la Zamboni):

    if (MusicList.HasItems)
    {
        Decorator border = VisualTreeHelper.GetChild(MusicList, 0) as Decorator;
        if (border != null)
        {
            ScrollViewer scrollViewer = border.Child as ScrollViewer;
            if (scrollViewer != null)
            {
                MusicList.ScrollIntoView(MusicList.SelectedItem);
            }
        }
    }

You get the next element seen at the bottom.

回答5:

I don't think ListBoxes have that, but ListViews have the EnsureVisible method that moves the scrollbar to the place needed in order to make sure an item is shown.

来源：https://stackoverflow.com/questions/159506/setting-the-scrollbar-position-of-a-listbox

标签

wpf

listbox

scrollviewer