我不明白为什么编译器要求在这个系统风格的UIBarButtonItem初始值设定项中为样式参数提供参数——它首先没有那个参数。帮助？这是Swift的错误吗？classExpensesViewController:UIViewController{lazyvarnewExpenseBarButtonItem=UIBarButtonItem(barButtonSystemItem:.Add,target:self,action:Selector("newExpenseBarButtonItemTapped:"))funcnewExpenseBarButtonItemTapped(){}}