Notifications can give people timely and important information, whether the device is locked or in use. For example, notifications can signal when a message arrives, an event is about to occur, new data is available, or there’s a status change. People appreciate receiving a notification for something they care about, but they don’t always appreciate being interrupted. To help people manage the overall experience, you need to get permission before sending any notifications.

User Notifications

Human Interface Guidelines: Managing notifications