アンカー/拘束をプログラムで使用するときにシミュレーションが空白の黒い画面になるのはなぜですか？

Question

ここに私のコードです。私は、ビューコントローラのトップレイアウトガイドの底に制約のWebViewアンカーの上部を作るしようとしているが、私はちょうどコンソールで黒い画面、時にはエラーを取得しています：

Unable to simultaneously satisfy constraints. 
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
     (1) look at each constraint and try to figure out which you don't expect; 
     (2) find the code that added the unwanted constraint or constraints and fix it. 
    (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<_UILayoutSupportConstraint:0x608000284d30 _UILayoutSpacer:0x6080001aa560'UIVC-topLayoutGuide'.height == 20 (active)>", 
    "<_UILayoutSupportConstraint:0x6080002850a0 V:|-(0)-[_UILayoutSpacer:0x6080001aa560'UIVC-topLayoutGuide'] (active, names: '|':UIView:0x7fcfcac26cd0)>", 
    "<NSAutoresizingMaskLayoutConstraint:0x608000280fa0 h=--& v=--& WKWebView:0x7fcfcb09a400.midY == 0 (active)>", 
    "<NSAutoresizingMaskLayoutConstraint:0x608000280ff0 h=--& v=--& WKWebView:0x7fcfcb09a400.height == 0 (active)>", 
    "<NSLayoutConstraint:0x6080002846f0 V:[_UILayoutSpacer:0x6080001aa560'UIVC-topLayoutGuide']-(3)-[WKWebView:0x7fcfcb09a400] (active)>", 
    "<NSAutoresizingMaskLayoutConstraint:0x608000281220 h=--& v=--& 'UIView-Encapsulated-Layout-Top' UIView:0x7fcfcac26cd0.minY == 0 (active, names: '|':UIViewControllerWrapperView:0x7fcfcac08120)>" 
) 

コード -

import UIKit 
import WebKit 

class webViewController: UIViewController, WKNavigationDelegate { 

    override func loadView() { 
     self.view = UIView() 
     let webView = WKWebView() 
//  webView.translatesAutoresizingMaskIntoConstraints = false 
     self.view.addSubview(webView) 

     let topConstraint = webView.topAnchor.constraint(equalTo: self.topLayoutGuide.bottomAnchor, constant: 3) 
     topConstraint.isActive = true 

     let url = NSURL(string: "https://www.google.com") 
     if let selectedURL = url { 
      let request = NSURLRequest(url: selectedURL as URL) as URLRequest 
      webView.load(request) 
     } 
    } 
} 

Answer 1

ナビゲーションデリゲートを追加します。次に

webView.navigationDelegate = self 

リットルエラーとナビゲーションの代理人に任せれば、実際に何が起こっているかどうかを見ることができます。