silverlight - How to detect scroll to top in LongListSelector?

Question

For WP8, I am using LongListSelector to display list of items. I need to detect when the user has scrolled to top to load previous items in the list.

I have tried using ItemRealized event to detect when top element has been realised. There are couple of references where it is used to detect 'scroll to bottom'.

• http://rahulpnath.wordpress.com/2013/03/03/windows-phone-series-incremental-loading/#comments
• http://code.msdn.microsoft.com/wpapps/TwitterSearch-Windows-b7fc4e5e

But this event gets fired for top element even when that user hasn't yet scrolled to that item. So, that doesn't for me to detect 'scrolling to top'.

Is there any way to detect this?

Answer 1

この参照を使用して垂直オフセットを取得できます LongListSelector の垂直オフセットを取得します

垂直オフセットが 0 (または 10 未満) の場合は、ViewPort の上にあります。

Answer 2

すでに使用している手法 ( ItemRealized) を使用しますが、最初のイベントを無視します (それはリストが作成されるときだからです。フラグを設定するだけで無視できます:

private bool _firstRealized = false;

void yourLLS_ItemRealized(object sender, ItemRealizationEventArgs e)
{
    // do your item detection here. For example:
    if (Data[0] == e.Container.Content) {

       // then
       if (!_firstRealized)
       {
          _firstRealized = true;
       }
       else
       {
          // woo - we've scrolled to top! Do your stuff
       }        
   }
}