ScrollViewer notify on RequestBringIntoView

问题

I am attempting to get notified when an element is scrolled into view ,

As i understand it , ScrollViewer calls BringIntoView on it's child elements and then the child elements raise a RequestBringIntoView event which the ScrollViewer later catches and handles.

This is done by Registering a Class handler for this Event and catching it as it bubbles up

EventManager.RegisterClassHandler(typeof(ScrollViewer), RequestBringIntoViewEvent, new RequestBringIntoViewEventHandler(OnRequestBringIntoView));

ScrollViewer Source Code

What i need is to get notified each time this process takes place , my attempt is to derive from ScrollViewer and Create my own event of type and approach it in one of 2 ways :

1) Add a class handler for that same event with a true at the end for handling Handled events .

2) Creating my own event which handles events of type RequestBringIntoViewEvent

public class NotifyOnBringIntoViewScrollViewer : ScrollViewer
{
    static NotifyOnBringIntoViewScrollViewer()
    {
        // for secnario (2) replace RequestBringIntoViewEvent with Noti
        EventManager.RegisterClassHandler(typeof(NotifyOnBringIntoViewScrollViewer),RequestBringIntoViewEvent , new RequestBringIntoViewEventHandler(OnRequestBringIntoView), true);                       
    }


    public static readonly RoutedEvent NotifyBringIntoViewEvent = EventManager.RegisterRoutedEvent(
                "NotifyBringIntoView", RoutingStrategy.Direct, typeof(RequestBringIntoViewEventHandler), typeof(NotifyOnBringIntoViewScrollViewer));

    private static void OnRequestBringIntoView(object sender, RequestBringIntoViewEventArgs e)
    {
        // notify ..
    }
}

The handler is never reached , for one or tow reasons ,

1) I miss understood the way routed events works in regard to registering handlers . 2) My child elements never raise RequestBringIntoView , my attempt for this is as follows :

cs :

   public List<int> Items
    {
        get
        {
            return new List<int>
            {
                1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25
            };
        }
    }

xaml :

  <local:NotifyOnBringIntoViewScrollViewer>
      <ItemsControl ItemsSource="{Binding Items}">

         <ItemsControl.ItemsPanel>
              <ItemsPanelTemplate>
                  <VirtualizingStackPanel />
              </ItemsPanelTemplate>
          </ItemsControl.ItemsPanel>

          <ItemsControl.ItemTemplate>
              <DataTemplate>
                  <TextBlock Text="{Binding}"/>
               </DataTemplate>
           </ItemsControl.ItemTemplate>                
       </ItemsControl>
    </local:NotifyOnBringIntoViewScrollViewer>

FYI : VirtualizingStackPanel , i put this because i wasn't sure that this is the default panel and if with out Virtualizing BringIntoView is ever called , since they are already in view.

来源：https://stackoverflow.com/questions/19475908/scrollviewer-notify-on-requestbringintoview

标签

wpf

virtualization

scrollviewer

routed-events