How to group user notifications using threadIdentifier and summaryArgument

Swift version: 5.6

Paul Hudson @twostraws November 1st 2019

If your app shows notifications that can be split into sensible groups – such as messages from a person, updates for a news story, scores from a sports match, and so on on – you can have iOS group them together using the threadIdentifier and summaryArgument properties of UNMutableNotificationContent. iOS will then show those messages together, rather than in a long chain mixed up with other messages.

For example, you might write code like this:

let content = UNMutableNotificationContent()
content.title = reminder.title
content.threadIdentifier = "F39-C521-A7A"

The “F39-C521-A7A” part is a free text string – it won’t be shown to users, but it’s what allows iOS to group things together so it should be unique enough that you don’t get message crossover. If you were building a messaging app you might use the user’s unique identifier for your notification rather than their name, to avoid two messages from different people called Andrew being grouped together.

If you want to customize this further, you can also set the summaryArgument property of your notification content. This is a string that is shown to users, so you might write something like this:

content.summaryArgument = messageSender.name

That will make iOS write something “5 more alerts from Andrew” in small text underneath the alert, which helps make it clear to users which reminder group that alert belongs to.