A toolbar button lets you offer important app functionality in a view that displays related content. Located at the top of a scrolling view, a toolbar button can stay hidden behind the navigation bar until people reveal it by scrolling up.
Toolbar buttons are available in watchOS 7 and later; for developer guidance, see ToolbarItemPlacement.primaryAction.
Place a toolbar button only in a scrolling view. People frequently scroll to the top of a scrolling view, so discovering a toolbar button is almost automatic. Placing a toolbar button in a nonscrolling view makes it permanently visible, eliminating the advantage of hiding it when it’s not needed.
Use a toolbar button for an important action that isn’t a primary app function. A toolbar button gives you the flexibility to offer important functionality in a view whose primary purpose is related to that functionality, but may not be the same. For example, Mail provides the essential New Message action in a toolbar button at the top of the Inbox view. The primary purpose of the Inbox is to display a scrollable list of email messages, so it makes sense to offer the closely related compose action in a toolbar button at the top of the view.
Prefer a single, full-width toolbar button. Displaying multiple toolbar buttons — whether stacked or side by side — can complicate the view and require people to make sure they’ve discovered the full set of actions before making a choice. If you’re considering more than one toolbar button, also consider whether your app needs a separate view to enable these essential actions.