ios - 为什么我的模拟以编程方式获得与 anchor /约束有关的空白黑屏？

这是我的代码。我试图将 webView anchor 的顶部限制在 View Controller 顶部布局指南的底部，但我只是得到一个黑屏，有时控制台中出现 错误:

 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 )>"
)

代码 -

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)
        }
    }
}

---

Best Answer-推荐答案

添加导航委托(delegate):

webView.navigationDelegate = self

然后听错误和导航代表，你将能够看到真正发生或没有发生的事情。

关于ios - 为什么我的模拟以编程方式获得与 anchor /约束有关的空白黑屏？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/41045099/