webView在iOS 8中为零，但在使用xib的iOS 9中不为零

Question

为什么在iOS 8中webView为空，而在iOS 9中不为空？

我应该如何在iOS 8中使用webview？以下是代码(swift 2.2)

在viewController类中：

@IBOutlet weak var webView: UIWebView!

override func viewDidLoad() {
    super.viewDidLoad()
    
    self.webView?.delegate = self   // without '?' in iOS 8 crash
                                    // in iOS 9 not crash
    
    // debug code
    if let webView = self.webView { // iOS 8 nil
        print("\(webView)")         // iOS 9 not nil
    }

    //...
}

谢谢!

Answer 1

class ViewController: UIViewController, UIWebViewDelegate {
@IBOutlet weak var webView: UIWebView!

let url = NSURL(string: "http://google.com")


override func viewDidLoad() {
    super.viewDidLoad()

    self.webView.delegate = self

    let req = NSURLRequest(URL : url!)
    self.webView.loadRequest(req)
}

func webViewDidStartLoad(webView: UIWebView) {
    print("start loading")
}

func webViewDidFinishLoad(webView: UIWebView) {
    print("finish loading")
}

//...

}

如下所示，此代码可以在iOS8和iOS9中完美运行

Answer 2

一种解决方案：

@IBOutlet weak var webViewXib: UIWebView!
var webView: UIWebView!

override func viewDidLoad() {
    super.viewDidLoad()

    if let _ = self.webViewXib {
    self.webView = self.webViewXib
    } else {
        self.webView = UIWebView()
        self.webView.frame = self.view.bounds
        self.view.addSubview(self.webView!)
    }
    self.webView!.delegate = self    

    // ...
}

Answer 3

问题在于实例化View Controller的方式，您可能会将其实例化为：

MyViewController *myViewController = [[MyViewController alloc] init]

这样，您就不会在viewDidLoad中准备好视图，相反，您应该尝试：

MyViewController *myViewController = [[MyViewController alloc] initWithNibName:"MyViewController" bundle:nil]