Classic AppKit autoscroll

AppKitAutoscroll.swift

import Cocoa

class MyAutoscrollingView: NSView {
    override func mouseDown(with event: NSEvent) {
        // mouseDown-specific logic here

        var mouseEvent = event
        var done = false
        NSEvent.startPeriodicEvents(afterDelay: 0.1, withPeriod: 0.05)

        while !done {
            guard let nextEvent = NSApp.nextEvent(matching: [.leftMouseUp, .leftMouseDragged, .periodic], until: .distantFuture, inMode: .eventTracking, dequeue: true) else {
                print("Unexpected nil event, should not expire")
                continue
            }

            switch nextEvent.type {
            case .periodic:
                autoscroll(with: mouseEvent)
                mouseDraggedOrAutoscroll(with: event)
            case .leftMouseUp:
                done = true
                NSApp.sendEvent(nextEvent)
            case .leftMouseDragged:
                mouseEvent = nextEvent
                NSApp.sendEvent(nextEvent)
            default:
                fatalError("unexpected event", nextEvent)
            }
        }

        NSEvent.stopPeriodicEvents()
    }

    override func mouseDragged(with event: NSEvent) {
        // mouseDragged-specific logic here
            
        mouseDraggedOrAutoscroll(with: event)
    }
    
    override func mouseUp(with event: NSEvent) {
        // mouseUp-specific logic here
    }

    func mouseDraggedOrAutoscroll(with event: NSEvent) {
        // things that should happen both on mouseDragged and on autoscroll
    }
}