     @IBOutlet weak var messageToolbar: MessageToolbar!
     @IBOutlet weak var messageToolbarBottomConstraint: NSLayoutConstraint!
 
+    let sectionInsetTop: CGFloat = 10
+    let sectionInsetBottom: CGFloat = 10
+
     let messageTextAttributes = [NSFontAttributeName: UIFont.systemFontOfSize(13)] // TODO: 用配置来决定
     let messageTextLabelMaxWidth: CGFloat = 320 - (15+40+20) - 20 // TODO: 根据 TextCell 的布局计算
 

        
        conversationCollectionView.bounces = true

        setConversaitonCollectionViewOriginalContentInset()

        messageToolbarBottomConstraint.constant = 0

        updateUIWithKeyboardChange = true

        return CGSizeMake(collectionViewWidth, height)
    }

    func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAtIndex section: Int) -> UIEdgeInsets {
        return UIEdgeInsets(top: sectionInsetTop, left: 0, bottom: sectionInsetBottom, right: 0)
    }

    func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
        view.endEditing(true)
    }
