Add a custom view to a page in Xamarin.iOS

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:

public class FloatingView : UIView
{
    public FloatingView() : base()
    {

    }

    public int PageNumber { get; set; }

    public pdftron.PDF.Rect PdfPageRect { get; set; }
}

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

var mCustomView = new FloatingView();
mCustomView.BackgroundColor = UIColor.Red;
mCustomView.PageNumber = 1;
mCustomView.PdfPageRect = new Rect(10, 10, 100, 100);
mPdfViewCtrl.OverlayView.AddSubview(mCustomView);

// 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:

void positionFloatingViews()
{
    foreach (UIView view in mPdfViewCtrl.OverlayView.Subviews)
    {
        if (view is FloatingView)
        {
            var overlayView = view as FloatingView;
            bool pageHidden = false;
            if (!mPdfViewCtrl.PagePresentationModeIsContinuous)
            {
                pageHidden = !mPdfViewCtrl.PageIsOnScreen(overlayView.PageNumber);
            }
            overlayView.Hidden = pageHidden;
            CGRect screenRect = mPdfViewCtrl.PDFRectPage2CGRectScreen(TypeConvertHelper.ConvRectToNative(overlayView.PdfPageRect), overlayView.PageNumber);
            screenRect.X += (nfloat)mPdfViewCtrl.GetHScrollPos();
            screenRect.Y += (nfloat)mPdfViewCtrl.GetVScrollPos();
            overlayView.Frame = screenRect;
        }
    }
}

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

mPdfViewCtrl.PdfViewCtrlOnLayoutChanged += (sender, e) =>
{
    positionFloatingViews();
};
mPdfViewCtrl.PdfScrollViewDidEndZooming += (sender, e) =>
{
    positionFloatingViews();
};