TableView with Diffable DataSource on MacOs

Question

I am writing an application using MacOs Big Sur with Xcode 12.2.

I am trying to implement a table view for a contact list (from examples on the internet).

Most of the code is for IOS en hard to port to MacOS.

For the most functionalities, the app is working very well.

I cannot succeed in implementing headers/footers for sections.

I did succeed with a previous project built around CollectionView.

But I cannot see the analogy between CollectionView and TableView. In CollectionView I used a nib for header/footers.

Here are the pieces of code for the Diffable Datasource example.

I hope somebody can help solving my problem.

'''
override func viewDidLoad() {
   tableView.delegate = self
   DataSource = makeDataSource()        
   tableView.dataSource = DataSource
   update(with:ContactList(all: Contact.all, 
          friends: [], 
          family: [], 
          coworkers: []),    
          animate: true)
}


func makeDataSource() -> NSTableViewDiffableDataSource<Section, Contact> {
    let reuseIdentifier = ContactTableCell.reuseIdentifier
    return NSTableViewDiffableDataSource( tableView: tableView, cellProvider: { tableView, column, indexPath, contact  in
        guard let cell = tableView.makeView(withIdentifier: NSUserInterfaceItemIdentifier(reuseIdentifier), owner: self) as? ContactTableCell else {
            print("Failed to create results cell")
            return NSView()
        }
        cell.configure(with: contact)
        return cell
    }
    )
}

func update(with list: ContactList, animate: Bool = true) {
    var snapshot = NSDiffableDataSourceSnapshot<Section, Contact>()
    snapshot.appendSections([Section.all, Section.family,Section.coworkers,Section.friends])
    
    snapshot.appendItems(list.all, toSection: .all)
    snapshot.appendItems(list.family, toSection: .family)
    snapshot.appendItems(list.coworkers, toSection: .coworkers)
    snapshot.appendItems(list.friends, toSection: .friends)
    
    DataSource.apply(snapshot, animatingDifferences: animate)
}

class ContactTableCell: NSTableCellView{

    @IBOutlet weak var firstname: NSTextField!
    @IBOutlet weak var lastname: NSTextField!
    @IBOutlet weak var email: NSTextField!
    @IBOutlet weak var userView: NSImageView!

    static var reuseIdentifier: String {
        return NSUserInterfaceItemIdentifier(String(describing: ContactTableCell.self)).rawValue
    }

    func configure(with contact:Contact){
        print("\(#function)")
        self.userView.imageScaling = .scaleProportionallyDown
        self.userView.image = NSImage(contentsOfFile:contact.imagePath)
        self.firstname.stringValue = contact.firstName //"\(contact.firstName) \(contact.lastName)"
        self.lastname.stringValue = contact.lastName  //contact.emailAddress
        self.email.stringValue = contact.emailAddress
    }
}

class SectionHeaderView: NSTableHeaderView {
static var reuseIdentifier: String {
    return NSUserInterfaceItemIdentifier(String(describing: SectionHeaderView.self)).rawValue
}

lazy var headerLabel: NSTextField = {
    print("\(#function)")
    let label = NSTextField()
    label.textColor = .red
    label.font = NSFont.systemFont(ofSize: 15, weight: .medium)
    label.translatesAutoresizingMaskIntoConstraints = false
    return label
}()
    
override  func draw(_ dirtyRect: NSRect) {
    print("\(#function)")
    super.draw(dirtyRect)
    // Drawing code here.
}

required  init?(coder: NSCoder) {
    print("\(#function)")
    super.init(coder: coder)
    setupView()
}

func setupView() {
    print("\(#function)")
    addSubview(headerLabel)
    setupLayout()
}

func setupLayout() {
    print("\(#function)")
    NSLayoutConstraint.activate([
        headerLabel.topAnchor.constraint(equalTo: self.topAnchor ,constant: 2),
        headerLabel.bottomAnchor.constraint(equalTo: self.bottomAnchor, 
                                            constant: -2),
        headerLabel.leadingAnchor.constraint(equalTo: self.leadingAnchor,
                                             constant: 8),
        headerLabel.trailingAnchor.constraint(equalTo: self.trailingAnchor,
                                            constant: -8),
    ])
}

} '''

Answer 1

A table view in macOS works a bit different, because there are no explicit sections like in iOS. The section headers are Group Rows which are inline as a part of the data source array.

To display section headers in the diffable data source create a struct rather than an enum

struct Section : Hashable {
    let name : String
}

Extend makeDataSource()

func makeDataSource() -> NSTableViewDiffableDataSource<Section, Contact> 
{
    let reuseIdentifier = ContactTableCell.reuseIdentifier
    let dataSource = NSTableViewDiffableDataSource<Section,Contact>( tableView: tableView, cellProvider: { tableView, column, row, contact  in
        let cell = tableView.makeView(withIdentifier: NSUserInterfaceItemIdentifier(reuseIdentifier), owner: self) as! ContactTableCell
        cell.configure(with: contact)
        return cell
    })

    dataSource.sectionHeaderViewProvider = { tableView, row, section in
        let cell = tableView.makeView(withIdentifier: NSUserInterfaceItemIdentifier(rawValue: "group"), owner: self) as! NSTableCellView
        cell.textField?.stringValue = section.name
        return cell
    }
    return dataSource
}

and populate the data source

func update(with list: ContactList, animate: Bool = true) {
    var snapshot = NSDiffableDataSourceSnapshot<Section, Contact>()
    let sections = [Section(name: "all"), Section(name: "family"), Section(name: "coworkers"), Section(name: "friends")

    snapshot.appendSections(sections)
    snapshot.appendItems(list.all, toSection: sections[0])
    snapshot.appendItems(list.family, toSection: sections[1])
    snapshot.appendItems(list.coworkers, toSection: sections[2])
    snapshot.appendItems(list.friends, toSection: sections[3])
    DataSource.apply(snapshot, animatingDifferences: animate)
}

Answer 2

I ran into a similar problem, and looking at the source code, what might need to be done in your case is set these to your diffableDataSource:

@property (copy,nullable) NSTableViewDiffableDataSourceRowProvider rowViewProvider;

@property (copy,nullable) NSTableViewDiffableDataSourceSectionHeaderViewProvider sectionHeaderViewProvider;

I don't think there is a section footer API, so you might need to show some sort of footer on the last cell item in the section.