A sidebar provides app-level navigation and quick access to top-level collections of content in your app. Selecting an item in the sidebar allows people to navigate to a specific piece of content. For example, the sidebar in Mail shows a list of all mailboxes. People can select a mailbox to access its list of messages, and select a specific message to display in the content pane.
You create a sidebar by using a sidebar-style list and placing it in the primary column of a split view. For related guidance, see Split Views.
Apply the correct appearance to a sidebar. To create a sidebar, use the sidebar appearance of a collection view list layout. For developer guidance, see UICollectionLayoutListConfiguration.Appearance.
Use a sidebar to organize information at the app level. A sidebar is a good way to flatten your information hierarchy and provide access to several peer information categories or modes at the same time. Use a sidebar for quick navigation to the key parts of the app or top-level collections of content like folders and playlists.
Whenever possible, let people customize the contents of a sidebar. Because a sidebar provides the navigation for your app, you can use it to provide shortcuts for people to get quickly to the content they care about. It’s best when the user can decide which items are most important.
Don't prevent people from hiding the sidebar. Allow people to hide the sidebar to create more room for their content, and to show the sidebar again using the built-in edge swipe gesture. Avoid making the sidebar hidden by default.
Keep titles in the sidebar clear and concise. Omit unnecessary and redundant words. For example, Mail omits the word Messages from the title of each mailbox, using more concise terms like Flagged and Drafts.
In general, refrain from exposing more than two levels of hierarchy within a sidebar. When a data hierarchy is deeper than two levels, use a list view in the supplementary column of a split-view interface.
For developer guidance, see UICollectionLayoutListConfiguration.