//1.添加返回按钮
func addBackBtn(){
let leftBtn:UIBarButtonItem=UIBarButtonItem(title: "返回", style: UIBarButtonItemStyle.Plain, target: self, action: "actionBack")
leftBtn.title="返回";
leftBtn.tintColor=UIColor.whiteColor();
self.navigationItem.leftBarButtonItem=leftBtn;
}
//返回按钮事件
func actionBack(){
self.navigationController?.popToRootViewControllerAnimated(true);
}