Load more items into ListBox when scrolled to bottom

问题

I've got ListBox bound to List. I want to load more items when scrolled to bottom of list so that some animation indicating loading is shown and bound list is expanded. If I understand correctly, I can use ObservableCollection instead of List and expand that collection. Also, I could wrap ItemPresenter into StackPanel with ItemPresenter and Image at bottom.

But how do I detect that list has been scrolled to bottom and initiate expanding of collection?

回答1:

Check tutorials:

http://blog.slimcode.com/2010/09/11/detect-when-a-listbox-scrolls-to-its-end-wp7/
http://danielvaughan.orpius.com/post/Scroll-Based-Data-Loading-in-Windows-Phone-7.aspx

回答2:

I found this http://blogs.microsoft.co.il/blogs/shair/archive/2011/04/06/wp7-how-to-extend-listbox-when-reaching-last-item.aspx in my opinion is more coincided, easy and self-explanatory than other examples.

回答3:

I'm use the following code to solve the same problem. As base I use the following solution, added one DependecyProperties and removed references on assembly Microsoft.Practices.Prism.Interactivity.

public class ScrollViewMonitor
{
    public static readonly DependencyProperty ReachBottomCommandProperty = DependencyProperty.RegisterAttached("ReachBottomCommand",
                            typeof(ICommand), typeof(ScrollViewMonitor), new PropertyMetadata(null, ReachBottomCommandChanged));


    public static ICommand GetReachBottomCommand(DependencyObject dpObj)
    {
        return  (ICommand)dpObj.GetValue(ReachBottomCommandProperty);
    }

    public static void SetReachBottomCommand(DependencyObject dpObj, ICommand command)
    {
        dpObj.SetValue(ReachBottomCommandProperty, command);
    }

    private static FrameworkElement _frmElemenet;

    private static void ReachBottomCommandChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
    {
       _frmElemenet = obj as FrameworkElement;

       if (_frmElemenet != null)
             _frmElemenet.Loaded += frmElement_Loaded;
    }


    public static readonly DependencyProperty VerticalOffsetProperty = DependencyProperty.RegisterAttached("VerticalOffset",
                            typeof(double), typeof(ScrollViewMonitor), new PropertyMetadata(0.0, VerticalOffsetChanged));

    private static void VerticalOffsetChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
    {
        ScrollViewer scrollView = (ScrollViewer)obj;

        if (scrollView.VerticalOffset > scrollView.ScrollableHeight * 0.8)
        {
            ICommand command = GetReachBottomCommand(_frmElemenet);

           if (command != null)
               command.Execute(null);
        }
    }

   private static void frmElement_Loaded(object sender, RoutedEventArgs e)
   {
       FrameworkElement frmElement = (FrameworkElement)sender;
       frmElement.Loaded -= frmElement_Loaded;

       var scrollView  = FindChildOfType<ScrollViewer>(frmElement);

       if (scrollView != null)
           scrollView.SetBinding(VerticalOffsetProperty, new Binding("VerticalOffset")
           {
               Source = scrollView
           }); 
   }


    private static T FindChildOfType<T>(DependencyObject obj) where T : class
    {
        Queue<DependencyObject> queue = new Queue<DependencyObject>();

        queue.Enqueue(obj); //Adds an object to the end of the

        while (queue.Count > 0)
        {
            DependencyObject current = queue.Dequeue(); //Removes and returns the object at the beginning of the Queue

            for (int i = 0, count = VisualTreeHelper.GetChildrenCount(current); i < count; i++)
            {
                DependencyObject dpObj = VisualTreeHelper.GetChild(current, 0);

                T typeChild = dpObj as T;
                if (typeChild != null)
                    return typeChild;

                queue.Enqueue(dpObj); //Adds an object to the end of the Queue
            }
        }

        return null;
    }
}

In XAML

       <ListBox x:Name="_lstBoxNews"
                     DataContext="{Binding Mode=OneTime}" 
                     ItemsSource="{Binding Items, Mode=OneWay}" 
                     ItemTemplate="{Binding Mode=OneWay, Source={StaticResource ShortArticleTemlate}}"
                     hlp:ScrollViewMonitor.ReachBottomCommand="{Binding LoadAdditionalArticles, Mode=OneTime}"
                     >
            </ListBox>

来源：https://stackoverflow.com/questions/9958138/load-more-items-into-listbox-when-scrolled-to-bottom

标签

windows-phone-7