A project to help me understand what is required to provide data for an NSOutlineView control

First up I'll try to get the File system example from the Outline View Programming Guide.

Steps followed to create the demo (Using Mac OS X Yosemite 10.10.1 and XCode 6)

• Created a new Swift project (Using storyboards cause I like them)

• Add a source list to the content view that has already been created (it is controlled by the ViewController class that has also already been created by the template).

• Mark the ViewController as conforming to the NSOutlineViewDelegate and NSOutlineViewDataSource protocols

• Back in IB link the NSOutlineView datasource and delegate outlets to the view controller (blue circle with white square inside that is at the top of the view)

• Create a new Cocoa class that is a subclass of NSObject. Name it FileSystemItem.

• Convert the Objective-C code from the example over to Swift. This was moderately tricky as the concepts between the two languages sometimes clash. I have tried to keep the code as close to the original as possible for now (though I will likely try and change it to more Swift like idioms once I understand the code better).

• Back in the View Controller I implemented the minimum set of data source methods, the method signatures are shown below in Swift.

    func outlineView(outlineView: NSOutlineView, 
    				 child index: Int, 
    				 ofItem item: AnyObject?) -> AnyObject { }
    				 
    func outlineView(outlineView: NSOutlineView, 
    	   isItemExpandable item: AnyObject) -> Bool { }
    	   
    func outlineView(outlineView: NSOutlineView, 
     numberOfChildrenOfItem item: AnyObject?) -> Int { }
     
    func outlineView(outlineView: NSOutlineView, 
       objectValueForTableColumn: NSTableColumn?, 
                          byItem:AnyObject?) -> AnyObject? { }
  

• With all that code filled in the application should run and should try to fill the NSOutlineView in with data. Unfortunately it won't get the path names right because by default the NSOutline view will be set to view based mode where as the example assumes cell based mode.

• In IB select the NSOutlineView (3 clicks). In the Attributes Inspector you can set the Content mode to Cell Based.

Now the application should run and show you the file system in the outline view.

There is a version of the same program which uses a view based outline view instead of a cell based view. It should operate exactly the same despite this difference. What needed to be changed between the two programs is listed below

• In IB set the Content Mode for the Outline View to View Based (this is the default)
• The datasource method objectValueForTableColumn: is no longer used. Instead the delegate method viewForTableColumn: is used to generate the content in each row/column. Inside this method we need to create a view to be displayed using makeViewWithIdentifier (look up NSTableView to find it).
• In IB you need to set the Identifier for your NSTableCellView to the string that you used in makeViewWithIdentifier (something like "DataCell")

The application should then run the same as the Cell based version.

Source list views are a little different from regular NSOutlineViews because they are often used to display groups of quite different objects. For instance in the Finder we have Favourites (Finder folders), Devices, Shared and Tags are all shown in the one Source List. For this reason I feel we should be able to map very different model objects into a source list without making everything come from the same base ItemClass. This has proven to be quite difficult for me to master.

Some of the issues and points of interest are

• It is important that every object in the model that will be displayed in the source list can be identified and can be used to create a table cell view by itself. The Genus and Species class in the project are good examples, the fauna array in the ViewController is a bad example (because it is hard to identify it from another array when it is passed in to the datasource methods).
• If the model objects don't subclass NSObject the program tends to crash.
• You can use arrays as the top container classes of your source list groupings, but it probably isn't a good idea. If you do (as I have done in this example) then you should use NSMutableArray rather than Swift arrays (it would crash for me using swift arrays).
• You can set the rows to display as group items which have a show/hide button rather than a reveal triangle by implementing the func outlineView(outlineView: NSOutlineView, isGroupItem item: AnyObject) -> Bool delegate method (Thanks to @cliftonlabrum for pointing that out).