Apple Watch通知中的图标按钮

Question

我的UI中有一个通知中带有图标的按钮。我已经通过代码

获得了按钮

 var approveAction = UIMutableUserNotificationAction()      
 approveAction.identifier = "approveButtonAction"      

 approveAction.title = "Approve"     

 approveAction.activationMode = UIUserNotificationActivationMode.Foreground    

 approveAction.destructive = false         

 approveAction.authenticationRequired = false      

但是如何在文本前面加上图标呢？ 请提供一些意见。