When you create a macOS Cocoa Application project, you project starts out with a Window Controller and a View Controller.
The Window Controller defines the actual window that appears on the screen but the View Controller defines the contents that appears inside the Window Controller. You need to place user interface items like buttons and text fields on the View Controller so when your program runs, these user interface items appear on the View Controller, which appears inside the Window Controller.
A View Controller represents a simple window, but Xcode offers several other types of view controllers such as a Page Controller, a Split View Controller, and a Tab View Controller. If you want any of these other types of controllers to appear inside the Window Controller, you need to follow two steps:
- Delete the currently existing View Controller
- Add the new controller you want to put in its place such as a Tab View Controller or Page Controller
To delete the existing View Controller, you need to delete both the View Controller in the storyboard and the ViewController.swift file. To delete the ViewController.swift file in the Navigator pane, just right-click over it and when a popup menu appears, choose Delete.
To delete the View Controller from the storyboard, select the View Controller by clicking the Show Document Outline icon and then clicking on View Controller Scene in the Document Outline. Then press Backspace or choose Edit > Delete.
Initially the contents of the Window Controller displayed View Controller but now it should display No Content View Controller.
Now drag another controller from the Object Library window to the storyboard such as Page Controller or Vertical Split Controller. This will place a new controller on the storyboard but now you’ll need to connect this newly added controller to appear inside the Window Controller.
Click on the blue icon that appears in the top, middle of the Window Controller. Hold down the Control key and Control-drag over the new controller you just added.
Release the Control key and the left mouse/trackpad button. A popup menu appears.
Choose window content. Your newly added controller now displays a connecting arrow to show that it appears inside the existing Window Controller.