         return messagesInConversation(self.conversation)
         }()
 
-    let messagesBunchCount = 12 // TODO: 分段载入的“一束”消息的数量
+    let messagesBunchCount = 50 // TODO: 分段载入的“一束”消息的数量
     var displayedMessagesRange = NSRange()
 
 


        // 初始时移动一次到底部
        if !conversationCollectionViewHasBeenMovedToBottomOnce {
            conversationCollectionViewHasBeenMovedToBottomOnce = true

            // 先调整一下初次的 contentInset
            setConversaitonCollectionViewOriginalContentInset()

            if displayedMessagesRange.length > 0 {
                conversationCollectionView.scrollToItemAtIndexPath(NSIndexPath(forItem: displayedMessagesRange.length - 1, inSection: 0), atScrollPosition: UICollectionViewScrollPosition.Bottom, animated: false)
            }


        }
    }
    
    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)
        conversationCollectionViewHasBeenMovedToBottomOnce = true
    }
    
    // MARK: UIScrollViewDelegate

    func scrollViewDidScroll(scrollView: UIScrollView) {
        pullToRefreshView.scrollViewDidScroll(scrollView)
        println("Scrolled\(scrollView.contentOffset.y)")
    }

    func scrollViewWillEndDragging(scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
