过渡到WebView之前先加载它

Question

我必须更新我一段时间没有触摸的应用程序，现在遇到致命错误：在执行webView.loadRequest（myRequest时）在DetailViewController :: refreshWebView（）中意外发现nil，同时展开了可选值），因为此时webView为零。

我没有更改与DetailViewController的加载方式以及如何将其分配给MasterViewController有关的任何事情，所以我很困惑，因为为什么这不再起作用。

我不知道有什么变化吗？还是我一开始就错误地实现了整个事情，并且巧合的是它起作用了？

import UIKit

protocol EventSelectionDelegate: class {
    func eventSelected(_ newEvent: String)
}

class MasterViewController: UIViewController, UIWebViewDelegate {

    var activityView: UIActivityIndicatorView!
    weak var delegate: EventSelectionDelegate?

    func detailChosen(_ detailUrlString: String) {
        delegate?.eventSelected(detailUrlString)
        activityView.startAnimating()
    }

    func transitionToDetail() {
        if let detailViewController = self.delegate as? DetailViewController {
            DispatchQueue.main.async {
                self.activityView.stopAnimating()
                self.splitViewController?.showDetailViewController(detailViewController, sender: nil)
            }
        }
    }
}

// Helper function inserted by Swift 4.2 migrator.
fileprivate func convertToUIApplicationOpenExternalURLOptionsKeyDictionary(_ input: [String: Any]) -> [UIApplication.OpenExternalURLOptionsKey: Any] {
    return Dictionary(uniqueKeysWithValues: input.map { key, value in (UIApplication.OpenExternalURLOptionsKey(rawValue: key), value)})
}

import UIKit

class DetailViewController: UIViewController, UIWebViewDelegate {

    @IBOutlet weak var webView: UIWebView!

    var animationWaitDelegate: MasterViewController!
    var eventUrl: String! {
        didSet {
            self.refreshWebView()
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        webView.delegate = self
    }

    func refreshWebView() {
        let myURL = URL(string:eventUrl!)
        let myRequest = URLRequest(url: myURL!)
        webView.loadRequest(myRequest)
    }

    func webViewDidFinishLoad(_ webView: UIWebView) {
        animationWaitDelegate.transitionToDetail()
    }
}

extension DetailViewController: EventSelectionDelegate {
    func eventSelected(_ newEvent: String) {
        eventUrl = newEvent
    }
}

// Helper function inserted by Swift 4.2 migrator.
fileprivate func convertToUIApplicationOpenExternalURLOptionsKeyDictionary(_ input: [String: Any]) -> [UIApplication.OpenExternalURLOptionsKey: Any] {
    return Dictionary(uniqueKeysWithValues: input.map { key, value in (UIApplication.OpenExternalURLOptionsKey(rawValue: key), value)})
}

PS：在此期间，我发现了一种解决方法，其中我在DetailViewController中添加了一个标志，如果webView首次被调用为零，则允许我在viewDidLoad中调用refreshWebView。

Answer 1

首先，您必须更新以下代码以进行空检查，这将防止您的应用崩溃。

func refreshWebView() {
    if webView != nil {
         let myURL = URL(string:eventUrl!)
         let myRequest = URLRequest(url: myURL!)
         webView.loadRequest(myRequest)
    }
}