贡献者:赵大财
博客:https://my.oschina.net/zhaodacaiGitHub:https://github.com/dacaizhao
邮箱: dacai_zhao@163.com QQ:327532817
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fileprivate func scrollToBottom(){
        if self.opVM.messageArr.count < 1 { return } else {
            let lastIndexPath = NSIndexPath(item: self.opVM.messageArr.count-1,section: 0)
            self.tableView .scrollToRow(at: lastIndexPath as IndexPath,at: .bottom,animated: false)
        }
    }