OutlineView | OutlineView for SwiftUI on macOS | Frontend Framework library

Dark mode causes some issues with printing. The easiest workaround is to create a separate, programmatic view with forced light appearance, clone the required content and then print that view.

view.appearance = NSAppearance(named: .aqua)

IMHO autosaving is sort of half-baked feature and it doesn't work as expected. In other words, it's implemented in a way that it restores the state when your application launches (just once) and then you're on your own.

Implement your own one utilizing outlineViewItemDidExpand(_:) & outlineViewItemDidCollapse(_:) (especially when we're reloading, ...).

Couple of tricks you can use if you do not want to implement custom autosaving. But I wouldn't rely on them.

NSOutlineView inherits from the NSTableView and the autosaveName property documentation says:

If you change the value of this property to a new name, the table reads in any saved information and sets the order and width of this table view’s columns to match. Setting the name to nil removes any previously stored state from the user defaults.

What is inaccurate here - setting it to nil doesn't remove previously stored expanded items state for NSOutlineView. We can use it to force the NSOutlineView to reload expanded items state:

Assuming your view controller view and TextView are already in window view hierarchy, do the following:

What is a source list? It's NSOutlineView (which is a subclass of NSTableView) with a special treatment. Finder screenshot:

To create a source list, all you have to do is to set the selectionHighlightStyle property to .sourceList. The documentation says:

The source list style of NSTableView. On 10.5, a light blue gradient is used to highlight selected rows.

What it does exactly? Jump to Definition in Xcode and read comments (not included in the docs):

The source list style of NSTableView. On 10.10 and higher, a blur selection is used to highlight rows. Prior to that, a light blue gradient was used. Note: Cells that have a drawsBackground property should have it set to NO. Otherwise, they will draw over the highlighting that NSTableView does. Setting this style will have the side effect of setting the background color to the "source list" background color. Additionally in NSOutlineView, the following properties are changed to get the standard "source list" look: indentationPerLevel, rowHeight and intercellSpacing. After calling setSelectionHighlightStyle: one can change any of the other properties as required. In 10.11, if the background color has been changed from the "source list" background color to something else, the table will no longer draw the selection as a source list blur style, and instead will do a normal blue highlight.

Since you're on Big Sur, be aware that the SelectionHighlightStyle.sourceList is deprecated. One should use style & effectiveStyle.

Xcode:

• New project
  • macOS & App (Storyboard & AppKit App Delegate & Swift)
• Main.storyboard
  • Add Source List control
    • Position & fix constraints
    • Set delegate & dataSource to ViewController
    • Enable Autosave Expanded Items
    • Set Autosave to whatever you want (I have FinderLikeSidebar there)
      • Choose wisely because the expansion state is saved in the user defaults under the NSOutlineView Items FinderLikeSidebar key
    • Create @IBOutlet var outlineView: NSOutlineView!
  • Add another Text Table Cell View (no image)
    • Set identifier to GroupCell
• ViewController.swift
  • Commented code below

As you can see, it's almost Finder like - 2nd level is still indented. The reason for this is that the Documents node is expandable (has children). I have them here to demonstrate autosaving.

Just remove them if you'd like to move all 2nd level nodes to the left.

There's not much to say about it except - read comments :)

Cocoa Bindings uses Key Value Observing (KVO) and the observed object must be KVO compatible. See Using Key-Value Observing in Swift.

You can only use key-value observing with classes that inherit from NSObject.

Mark properties that you want to observe through key-value observing with both the @objc attribute and the dynamic modifier.

Solution A: Return a KVO compatble object from outlineView(_:objectValueFor:byItem:)

Solution B: Don't use Cocoa Bindings. Create a subclass of NSTableCellView and add a enabledCheckbox outlet. Set the values in outlineView(_:viewFor:item:).

0 ..< self.numberOfRows is a Range and in particular a Sequence. Iterating over a sequence is done by creating an iterator, and then calling its next() method until the iterator is exhausted, compare IteratorProtocol:

Whenever you use a for-in loop with an array, set, or any other collection or sequence, you’re using that type’s iterator. Swift uses a sequence’s or collection’s iterator internally to enable the for-in loop language construct.

So

Recursion, expand the parent before expanding the node:

The prepareForSegue code reveals the mistake:

You are setting echo in prepareForSegue. This causes to call the property observer didSet. However at this moment the view is not loaded yet and force unwrapping the type crashes.

The solution is to move the code in didSet into viewDidLoad and viewWillAppear and delete the property observer. Nevertheless I recommend to optional bind window

Here you go: