The official name is “Navigate to Related Items” but to me, it’s the four block wonder, a menu button that sits at the top left of the Xcode editor. With this menu, you can hop between file counterparts (for example, .m/.h, or .swift/generated interface, which is what a lot of people use it for). But there’s so much more.
Set the cursor on a type, and you can view or navigate its superclass, subclasses, or siblings, as well as the protocols, extensions, and categories it connects to. A single click navigates you to the interface or implementation in question:
Use the cursor to establish the context for the menu, otherwise you’ll only see a smaller subset menu options, such as recent files. The callers option shows you your clients, and callees the items your code is calling — all specific to the current cursor context.
One of my favorite tools in the four-block menu is Generated Interfaces, which allows you to view an item’s Swift interface or see how it translates to Objective-C. For example, if you use an obvious preposition label, the ObjC generated interface subsumes it into its selector:
With this, you don’t have to wonder if your selector is specified right and you don’t have to override the selector with
objc. You just look up the definition and you’re good to call.
In addition to contextual helpers, the four-block lets you select recently viewed files and, when using version control, recent files that have been locally modified and not yet committed (basically the ones showing the “M”-for-modified).
The four little squares may be tiny but it is a powerful tool in your Xcode arsenal.
Update: Lilly reminds me that you can bind the related items menu. I have mine bound to ^1 but I don’t remember if that’s something I did or something that is default. If you want to add or change, visit Preferences > Key Bindings and search for “related”.