Printing multi-page content in macOS - draw method only called for first page

Question

I'm trying to implement printing for a macOS app. I've created a custom NSView class to handle it as described in the Apple Developer documentation. To facilitate multi-page printing, I've followed the guidance at the Laying Out Page Content page.

My PrintView class code looks like this:

import Cocoa

class PrintView: NSView {
    let configuration: PrintConfiguration // a struct with some margin info and helpers
    let info = NSPrintInfo.shared
    private(set) var pageNum = 0
    
    private(set) var ranges: [NSRange] = [] // array of pre-calculated page content
    private(set) var content: NSAttributedString 

    override var isFlipped: Bool {
        return true
    }
    
    init(printContent: NSAttributedString, config: PrintConfiguration, ranges: [NSRange]) {
        self.content = printContent
        self.ranges = ranges
        self.configuration = config
        super.init(frame: CGRect(origin: .zero, size: info.paperSize))
        self.frame.size.height = config.printHeight
        info.verticalPagination = .automatic
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    
    override func draw(_ dirtyRect: NSRect) {
        print("Entering draw - dirtyRect: \(dirtyRect)")
        
        let rangeNum = pageNum - 1 // adjust to 0-based for accessing array
        let range = ranges[rangeNum]
        let text = self.content.attributedSubstring(from: range)
        let drawRect = configuration.printRect
        text.draw(in: drawRect)
    }
    
    override func knowsPageRange(_ range: NSRangePointer) -> Bool {
        print("Entering knowsPageRange")
        range.pointee.location = 1
        range.pointee.length = self.ranges.count
        
        print("Page range: \(range.pointee)")
        return true
    }
    
    override func rectForPage(_ page: Int) -> NSRect {
        print("Entering rectForPage")
        self.pageNum = page
        let pageHeight = configuration.printHeight
        let pageNum = CGFloat(page - 1)
        let printRect = CGRect(x: configuration.leftMargin,
                               y: (pageNum * pageHeight) + configuration.topMargin,
                               width: configuration.printWidth,
                               height: configuration.printHeight)
        print("Print rect: \(printRect)")
        return printRect
    }
    
    override func locationOfPrintRect(_ rect: NSRect) -> NSPoint { // only included this method to see if it's called -- it doesn't appear to be required for my implementation
        print("Entering locationOfPrintRect")
        return NSPoint(x: self.configuration.leftMargin, y: self.configuration.topMargin)
    }
}

Then from a view's print method, I can call it thusly:

        let printView = PrintView(printContent: text, config: printConfiguration, ranges: ranges)

        let info = NSPrintInfo.shared
        
        let printOp = NSPrintOperation(view: printView, printInfo: info)
        printOp.jobTitle = title // a view property
        printOp.canSpawnSeparateThread = true
        printOp.run()

And when I invoke that from my running application with text that should extend to two pages, I get the following in my console:

Entering knowsPageRange
Page range: {1, 2}
Entering knowsPageRange
Page range: {1, 2}
Entering rectForPage
Print rect: (40.0, 80.0, 532.0, 652.0)
Entering locationOfPrintRect
Entering draw - dirtyRect: (40.0, 80.0, 532.0, 572.0)
Entering rectForPage
Print rect: (40.0, 732.0, 532.0, 652.0)
Entering locationOfPrintRect

In other words, all the methods I expect to be called twice (once for each page) are called twice (or more in the case of knowsPageRange), except for the draw method. And as expected with that behavior, only the first page is rendered. The print preview dialog does show two pages to be printed, but the second page is blank.

Likewise if I choose the print dialog option to send the print job to the Preview app, it only shows the first page of text.

After writing my question initially I walked the dog and it occurred to me that I should try it with text that should extend the text to more than two pages worth. When I got back and did that, it again created the correct number of pages, but only draws text for the first page. However, with 6 pages worth of text, the pagination methods are only called three times:

Entering knowsPageRange
Page range: {1, 6}
Entering knowsPageRange
Page range: {1, 6}
Entering rectForPage
Print rect: (40.0, 80.0, 532.0, 652.0)
Entering locationOfPrintRect
Entering draw - dirtyRect: (40.0, 80.0, 532.0, 572.0)
Entering rectForPage
Print rect: (40.0, 732.0, 532.0, 652.0)
Entering locationOfPrintRect
Entering rectForPage
Print rect: (40.0, 1384.0, 532.0, 652.0)
Entering locationOfPrintRect

I'd appreciate it if somebody can tell me what I'm doing wrong.

Answer 1

Thanks to @Willeke steering me in the right direction, my code now works with the following change to the rectForPage method:

    override func rectForPage(_ page: Int) -> NSRect {
        self.pageNum = page
        let printRect = CGRect(x: configuration.leftMargin,
                               y: configuration.topMargin,
                               width: configuration.printWidth,
                               height: configuration.info.paperSize.height - configuration.bottomMargin)
        return printRect
    }