How to solve dynamic height UIWebView issue with ScrollView?

Question

iOS

Please help me understand dynamic UIWebView. There is a controller with the following constraints (constraints)
The controller itself:

import Foundation
import UIKit

class ViewOnePageController : AbstractChildController, UIWebViewDelegate{

@IBOutlet weak var titletext: UILabel!
@IBOutlet weak var date: UILabel!
@IBOutlet weak var web: UIWebView!

var page : OtherPage!

override func viewDidLoad() {
    super.viewDidLoad()

    titletext.text = page.title
    date.text = "Last Updated: "+Convertor.dateToString(page.parseDate/1000)

    web.delegate = self
    web.scrollView.scrollEnabled = false
    web.scrollView.bounces = false
    web.scrollView.showsHorizontalScrollIndicator = false
    web.scrollView.showsVerticalScrollIndicator = false
    for subview in web.subviews {
        if subview.isKindOfClass(UIScrollView) {
            for shadowView in subview.subviews {
                if shadowView.isKindOfClass(UIImageView) {
                    (shadowView as UIView).hidden = true
                }
            }
        }
    }
    web.loadHTMLString(page.text, baseURL: nil)

}


func webViewDidFinishLoad(webView: UIWebView) {
    if let output:NSString! = webView.stringByEvaluatingJavaScriptFromString("document.height;") {

        if let height:Double = output.doubleValue {

            let heightConstraint = webView.constraints[0] as NSLayoutConstraint
            // here is to update the height of UIWebView
            heightConstraint.constant = CGFloat(height)
        }
    }
}

override func getTitle() -> String {
    return page.title
}

override func back() {
    self.navigationController?.popViewControllerAnimated(true)
}
}

For some reason, vertical scrolling doesn't work completely.