Question

Xamarin Forms应用程序在单击“导航按钮”期间抛出以下错误。如果我在import UIKit import WebKit class ViewController: UIViewController, WKNavigationDelegate { var webView: WKWebView! var progressView: UIProgressView! var websites = ["apple.com", "google.com"] //loadView() func override func loadView() { //create an instance of WKWebView() webView = WKWebView() webView.navigationDelegate = self view = webView } override func viewDidLoad() { super.viewDidLoad() //get URL and make a load URLRequest guard let url = URL(string: "https://www." + websites[0]) else { return } webView.load(URLRequest(url: url)) webView.allowsBackForwardNavigationGestures = true //set BarButtonItem on the top right of page navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Open", style: .plain, target: self, action: #selector(openTapped)) //add UIToolbar items with UIBarButtonItems let spacer = UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: nil, action: nil) let reload = UIBarButtonItem(barButtonSystemItem: .refresh, target: webView, action: #selector(webView.reload)) //add progressView progressView = UIProgressView(progressViewStyle: .default) progressView.sizeToFit() let progressButton = UIBarButtonItem(customView: progressView) //add items to toolbarItems array toolbarItems = [progressButton, spacer, reload] navigationController?.isToolbarHidden = false //create actionSheet UIAlertActionController for bar button drop down @objc func openTapped() { let alert = UIAlertController(title: "Open new page!", message: nil, preferredStyle: .actionSheet) for website in websites { alert.addAction(UIAlertAction(title: website, style: .default, handler: openPage)) } alert.addAction(UIAlertAction(title: "Cancel", style: .cancel)) alert.popoverPresentationController?.barButtonItem = self.navigationItem.rightBarButtonItem present(alert, animated: true) } //handlers for each UIAlertAction func openPage(action: UIAlertAction) { guard let actionTitle = action.title else { return } guard let url = URL(string: "https://" + actionTitle) else { return } webView.load(URLRequest(url: url)) } //set webView title to web page title func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) { title = webView.title }类中评论以下方法DisplaySoccerStatus();，则该应用程序将运行。因此，我认为数据库中很少有记录为空会导致此问题？不确定，如何解决该问题？

SoccerDailyStatus

SQLite.SQLiteException: Could not open database file: /data/user/0/com.companyname.soccerapp/files/.config/soccerpep (CannotOpen

}

堆栈跟踪：

 public partial class SoccerDailyStatus : ContentPage
{
    private SQLiteConnection conn;
    SoccerAvailability status; 

    public SoccerDailyStatus(SoccerAvailability soccerStatus)
    {
        InitializeComponent();
        status = soccerStatus;
        BindingContext = status;
       //DisplaySoccerStatus();
    }

    protected override async void OnAppearing()
    {
        conn = DependencyService.Get<Isqlite>().GetConnection();
        conn.CreateTable<SoccerAvailability>();
        base.OnAppearing();

        async Task DisplaySoccerStatus()
        {
            var datetoday = DateTime.Now.ToString("ddMMyyyy");
            //List<SoccerAvailability> myList = (from x in conn.Table<SoccerAvailability>() select x).ToList();
            List<SoccerAvailability> myList = (from x in conn.Table<SoccerAvailability>().Where(x => x.CurrentDate == datetoday) select x).ToList();
            if (myList != null)
            {
                SoccerAvailability soccerAvailability = new SoccerAvailability();
                soccerAvailability.SoccerStatus = myList[0].SoccerStatus;
                soccerAvailability.CurrentDate = DateTime.Now.ToString("ddMMyyyy");
                await Navigation.PushAsync(new SoccerDailyStatus(soccerAvailability) { });
            }
            else
            {
                await DisplayAlert("Notification", "Unable to proccess status", "Cancel");
            }

        }

        await DisplaySoccerStatus();
    }


}

Answer 1

我认为问题是由于ctor中调用了async方法DisplaySoccerStatus造成的。单个数据连接不能同时在两个或多个线程中使用。

我建议两件事：

在DisplaySoccerStatus中呼叫您的async onAppearing，然后使用await DisplaySoccerStatus。哦，请使用async Task DisplaySoccerStatus而不是async void，以便您知道任务何时完成。

异步无效情况是一种“失控”：您启动了任务链，但并不关心它何时完成。函数返回时，您所知道的就是直到第一次等待的所有操作都已执行。第一次等待后的所有内容都将在将来无法访问的某个特定时间运行。

按照official documentation

Xamarin Forms应用程序抛出“ SQLite.SQLiteException：无法打开数据库文件”

1 个答案: