Welcome to a new tutorial where we are going to unfold another cool topic on macOS programming. Today we are going to meet an important control, really useful for displaying hiearchical data, the outline view.
Outline view inherits from table view, so there are significant similarities to the way we handle both. Table views have been the topic of this previous post, and I strongly recommend you to read it before you go to this one if you haven’t done so. What makes outline views a unique control is that displayed data can be expanded and collapsed, just like the directories and subdirectories in Finder on macOS, to the Groups and their contents in Project Navigator in Xcode, or the Document Outline in Interface Builder.
Configuring the user interface of an outline view is identical to the way the interface of a table view is configured. There are columns, cell views, identifiers, cell view subclassing, and so on; in general almost everything we met in the previous post discussing about table views. The delegate method to load cell views from the storyboard and set them up is also similar to the table view’s. What changes is the way we set the data source of the outline view. Additionally, we don’t have to deal with index paths here; instead there’s the concept of the item, where an item actually matches to an object of the data source. You will see how we treat items soon enough.
Through the following parts we will learn how to create an outline view, how to configure it, and how to deal with items and other important stuff. Being able to show expandable and hierarchical data is mandatory for a macOS developer, and today you’ll learn all you need so you can integrate outline views in your apps. Once again we’ll build a small application which you can then change or enrich and use it as you like.