在转换之前加载 WebView

Question

我不得不更新一个我已经有一段时间没有接触过的应用程序，现在在执行 webView.loadRequest(myRequest) 时面临 DetailViewController::refreshWebView() 中的 'Fatal error: Unexpectedly found nil while unwrapping an Optional value' 因为此时 webView 为零。

我没有更改与 DetailViewController 如何加载和分配给 MasterViewController 相关的任何内容，所以我很困惑为什么这不再起作用。

有什么我不知道的变化吗？还是我一开始就错误地实施了这整个事情，而它起作用只是巧合？

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：我同时找到了一个解决方法，我在 DetailViewController 中添加了一个标志，如果 webView 第一次被调用时为 nil，我可以在 viewDidLoad 中调用 refreshWebView。

Answer 1

首先，您必须更新以下代码以进行空值检查，这将防止您的应用程序崩溃。

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

转换后添加以下代码将解决您的问题。

func transitionToDetail() {
    if let detailViewController = self.delegate as? DetailViewController {
        DispatchQueue.main.async {
            self.activityView.stopAnimating()
            detailViewController.loadViewIfNeeded()   // Add this line of code
            self.splitViewController?.showDetailViewController(detailViewController, sender: nil)
        }
    }
}

loadViewIfNeeded() 方法将在需要时在打开屏幕之前加载您的控件。

在转换之前加载 WebView

Load WebView before transitioning to it

uiwebview

ios

swift