Why WKWebView becomes nil?

Question

I use Swift4.0 and Xcode9.0. I try to show a website using WKWebView. It had no problem until yesterday, but today an error occurred.

import UIKit
import WebKit

class WKWebViewViewController: UIViewController, WKUIDelegate, WKNavigationDelegate {

    @IBOutlet weak var webView: WKWebView!

    var startUrl = "https://www.apple.com"
    var requestUrl: String?

    override func loadView() {
        webView.uiDelegate = self
        webView.navigationDelegate = self

    }

    override func viewDidLoad() {
        super.viewDidLoad()

        webView.allowsBackForwardNavigationGestures = true

        if let url = URL(string: startUrl) {
            let request = URLRequest(url: url)
            webView.load(request)

        }

    }

}

The error occurs at webView.uiDelegate = self. Here's the error log:

fatal error: unexpectedly found nil while unwrapping an Optional value

For debug, I added print("webView:\(webView)") under loadView(), and I found webView itself is nil.

I tried to add ? to all webView, but only black screen appeared on the app. Why WkWebView becomes nil? Is it some required setting outside my code?

Answer 1

You must call super.loadView() when you override loadView this way. This is why the WKWebView is nil.

The docs suggest not overriding loadView at all when using a storyboard/xib

If you use Interface Builder to create your views and initialize the view controller, you must not override this method.

You should move those 2 lines of code as the second thing in viewDidLoad

override func viewDidLoad() {
    super.viewDidLoad()
    webView.uiDelegate = self
    webView.navigationDelegate = self
    ....
}