!TableTooltip.md

This gist shows how to add a tooltip including a button to show it in a header of a table created using SwiftUI. It is used in ASO Suite.

AnyHashable+Additions.swift

import Foundation

extension AnyHashable {
    
    struct tooltip {
        static let tag = "tooltip.tag"
        static let point = "tooltip.point"
    }
}

Notification+Additions.swift

import Foundation

extension Notification.Name {
    
    static let tooltipButtonClicked = Notification.Name("tooltipButtonClicked")
}

TableWithTooltips.swift

import SwiftUI
import Introspect // https://github.com/siteline/SwiftUI-Introspect

struct Item: Identifiable {
    var id = UUID()
    var name: String
}

struct TableWithTooltips: View {
    
    @State var items: [Item] = [
        Item(name: "Some item"),
        Item(name: "Another item"),
        Item(name: "Yet another item")
    ]
    @State private var tooltipVisibleForColumn: Int?
    @State private var tooltipAnchorPoint = NSZeroPoint
    
    var body: some View {
        Table(items) {
            TableColumn("Name") {
                Text($0.name)
            }
        }
        .introspectTableView { tableView in
            let column = 0
            let title = tableView.tableColumns[column].title
            tableView.tableColumns[column].headerCell = TooltipHeaderCell(textCell: title, tag:column)
        }
        .popover(isPresented: showingTooltip, attachmentAnchor: .rect(.rect(CGRect(x: tooltipAnchorPoint.x, y: tooltipAnchorPoint.y, width: 0, height: 0))), arrowEdge: .bottom, content: {
            VStack {
                Text("Hello!")
            }
            .padding()
            .frame(width: 250)
        })
        .onReceive(NotificationCenter.default.publisher(for: .tooltipButtonClicked)) { notification in
            if let userInfo = notification.userInfo {
                if let tag = userInfo[.tooltip.tag] as? Int, let point = userInfo[.tooltip.point] as? NSPoint {
                    tooltipVisibleForColumn = tag
                    tooltipAnchorPoint = point
                }
            }
        }
    }
    
    private var showingTooltip: Binding<Bool> {
        return Binding(
            get: { tooltipVisibleForColumn != nil },
            set: { if !$0 { tooltipVisibleForColumn = nil } }
        )
    }
}

struct TestTable_Previews: PreviewProvider {
    static var previews: some View {
        TableWithTooltips()
    }
}

TooltipHeaderCell.swift

import Foundation
import AppKit

class TooltipHeaderCell: NSTableHeaderCell {

    init(textCell: String, tag: Int) {
        super.init(textCell: textCell)
        self.tag = tag
    }
    
    required init(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func drawInterior(withFrame cellFrame: NSRect, in controlView: NSView)
    {
        super.drawInterior(withFrame: cellFrame, in: controlView)
        for subview in controlView.subviews {
            if subview.tag == tag {
                subview.removeFromSuperview()
            }
        }
        if cellFrame.origin.x == 0 {
            return
        }
        let attributes: [NSAttributedString.Key: Any] = (font != nil) ? [.font: font!] : [:]
        let titleWidth = (title as NSString).size(withAttributes: attributes).width
        let x = titleRect(forBounds: cellFrame).origin.x + titleWidth + 15
        let frame = NSRect(x: x, y: titleRect(forBounds: cellFrame).origin.y, width: cellFrame.height, height: cellFrame.height)
        let button = NSButton(frame: frame)
        button.tag = tag
        button.image = NSImage(systemSymbolName: "info.circle.fill", accessibilityDescription: nil)
        button.imagePosition = .imageOnly
        button.isBordered = false
        button.target = self
        button.action = #selector(buttonClicked(_:))
        controlView.addSubview(button)
    }

    @objc func buttonClicked(_ sender: NSButton) {
        let point = NSPoint(x: sender.frame.midX, y: sender.frame.maxY)
        NotificationCenter.default.post(name: .tooltipButtonClicked, object: self, userInfo: [
            .tooltip.tag: tag,
            .tooltip.point: point
        ]) // Click handler is prefered, but that caused a crash so using a notification instead.
    }
}