NSScrollView not scrolling

Question

I have a form in a Mac app that needs to scroll. I have a scrollView embedded in a ViewController. I have the scrollView assigned with an identifier that links it to its own NSScrollView file. The constraints are set to the top, right, and left of the view controller, it also has the hight constraint set to the full height of the ViewController.

Here is my code:

import Cocoa

class ScrollView: NSScrollView {

override func draw(_ dirtyRect: NSRect) {
    super.draw(dirtyRect)

    // Drawing code here.
    NSRect documentView.NSMakeSize(0, 0, 1058.width, 1232.height)
}

override func scrollWheel(with event: NSEvent) {
    switch event.phase {
    case NSEvent.Phase.began:
        Swift.print("Began")
//        case NSEvent.Phase.changed:
//            Swift.print("Changed")
    case NSEvent.Phase.ended:
        Swift.print("Ended")
    default:
        break
    }

    switch event.momentumPhase {
    case NSEvent.Phase.began:
        Swift.print("Momentum Began")
//        case NSEvent.Phase.changed:
//            Swift.print("Momentum Changed")
    case NSEvent.Phase.ended:
        Swift.print("Momentum Ended")
    default:
        break
    }
    super.scrollWheel(with: event)
}

I cant seem to get my app to scroll at all. I think I am not setting the frame correctly. What is the best way to do set the frame correctly? Am I coding the NSScrollView correctly?

What’s your recommendation? – Cartisim Oct 30 '18 at 00:28 — Cartisim, Oct 30 '18 at 00:28

score 4 · Accepted Answer · answered Oct 29 '18 at 23:43

I think you are making your life very hard because you are doing things that are not exactly recommended by Apple. First of all, you should not subclass NSScrollView. Rather you should read first Introduction to Scroll View Programming Guide for Cocoa by Apple to understand how you should create the correct hierarchy of views for an NSScrollView to work correctly.

A second recommendation is for you to check this nice article about how you should set up an NSScrollView in a playground, so that you can play with the code you want to implement.

Third, using Autolayout and NSScrollView has caused a lot of grief to a lot of people. You need to set up the AutoLayout just right, so that everything is going to work as expected. I recommend that you check this answer by Ken Thomases, which clearly explains how you need to set up auto layout constraints for an NSScrollView to work properly.

score 0 · Answer 2 · edited Mar 22 '20 at 07:13

I just got over the "hump" with a NSScrollView inside a NSWindow. In order for scrolling to occur the view inside the NSScrollview needs to be larger than the content window. That's hard to set with dynamic constraints. Statically setting the inner view to a larger width/height than the window "works" but the static sizes usually are not what you want.

Here is my interface builder view hierarchy and constraints, not including the programmatically added boxes

In my app the user is adding "boxes" (custom draggable views) inside the mainView, which is inside a scrollview in a NSwindow.

Here's the functionality I wanted:

If I expanded the NSWindow, I wanted the mainView inside the scrollview to expand to fill the whole window. No scrolling needed in this case if all the boxes are visible.
If I shrank the NSWindow, I wanted the mainView inside the scrollview to shrink just enough to include all my mainView subviews ("boxes"), but not any further (i added a minBorder of 20). This results in scrolling if a box's position is further right/up than the nswindow's width/height.

I found the trick is to calculate the size of the mainView I want based on the max corner of each draggable boxview, or the height/width of the content frame of the nswindow, whichever is larger.

Below is my code, including some debugging prints.

Be careful of which subviews you use to calculate the max size. If you include a subview that's dynamically attached to the right/top of the window, then your window will never shrink. If you add +20 border to that, you might infinite loop. Not a problem in my case.

extension MapWindowController: NSWindowDelegate {
    func windowDidEndLiveResize(_ notification: Notification) {
        if let frame = window?.frame, let content = window?.contentRect(forFrameRect: frame) {
            print("window did resize \(frame)")
            var maxX: CGFloat = content.width
            var maxY: CGFloat = content.height
            for view in mainView?.subviews ?? [] {
                let frameMaxX = view.frame.maxX + minBorder
                let frameMaxY = view.frame.maxY + minBorder
                if frameMaxX > maxX {
                    maxX = frameMaxX
                }
                if frameMaxY > maxY {
                    maxY = frameMaxY
                }
            }
            print("view maxX \(maxX) maxY \(maxY)")
            print("window width \(content.width) height \(content.height)")
            mainView?.setFrameSize(NSSize(width: maxX, height: maxY))
        }
    }
}

NSScrollView not scrolling

2 Answers2