Add a UIView to a PDF page

It is convenient for the user to make a UIView that is "stuck" to a page record its desired page location. To do this, you could add an extension/category to a UIView, or use a derived class, as shown below:

class FloatingView: UIView {
    // the page on which the UIView appears
    
    var pageNumber: Int32 = 0
    // the location, expressed in PDF coordinates, at which the view appears
    var pdfPageRect: PTPDFRect?
}

In this example, we will add a red square to a location near the bottom left hand corner of the first page:

// prepare the new view
let redRect = FloatingView()
redRect.backgroundColor = UIColor.red
redRect.pageNumber = 1
redRect.pdfPageRect = PTPDFRect(x1: 10, y1: 10, x2: 100, y2: 100)

// add the view to PTPDFViewCtrl's overlayView
self.pdfViewCtrl.overlayView.addSubview(redRect)

// position the view
positionFloatingViews()

Without the last line in the code snippet above, the new view would not appear in the correct location. The following method will position it, and any others that have been added:

func positionFloatingViews() {
    for case let overlayView as FloatingView in self.pdfViewCtrl.overlayView.subviews {
        // make sure this is a floating view
        if type(of: overlayView) === FloatingView.self {
            var pageHidden = false
            if !pdfViewCtrl.pagePresentationModeIsContinuous() {
                pageHidden = !pdfViewCtrl.pageIs(onScreen: overlayView.pageNumber)
            }
            overlayView.isHidden = pageHidden
            var screenRect: CGRect = pdfViewCtrl.pdfRectPage2CGRectScreen(overlayView.pdfPageRect, pageNumber: overlayView.pageNumber)
            screenRect.origin.x += CGFloat(pdfViewCtrl.getHScrollPos())
            screenRect.origin.y += CGFloat(pdfViewCtrl.getVScrollPos())
            overlayView.frame = screenRect
        }
    }
}

func pdfViewCtrl(_ pdfViewCtrl: PTPDFViewCtrl!, pdfScrollViewDidEndZooming scrollView: UIScrollView!, with view: UIView!, atScale scale: Float) { positionFloatingViews() }