WebView即使应用处于后台/关闭状态(前台服务处于活动状态)如何运行 [英] WebView How to run even when app is in background/closed (foreground service active)

问题描述

我正在构建一个应用程序，该应用程序将从网站上抓取一些数据，并在满足某些条件时显示通知.

I'm building an app which will scrape some data from a website and shows a notification when some criteria are met.

在打开应用程序(因为正在渲染WebView)时，一切工作正常，但没有问题，但是当我关闭应用程序时，WebView被禁用，因此我无法再使用它来抓取数据.

Everything works well without problems when the app is open (because the WebView is being rendered) but when I close the app the WebView is disabled so I cannot use it to scrape data anymore.

抓取代码位于从ForegroundService调用的类中.

The scraping code is inside a class called from a ForegroundService.

我已经看过Internet，但是找不到WebView的解决方案或替代品，您有什么想法吗?

I've already looked on the internet but I'm unable to find a solution or a substitute to WebView, do you have any ideas?

很抱歉，如果您觉得这个问题很愚蠢，就在一周前，我就开始开发移动版

I'm sorry if this question looks stupid to you, I've started to develop for mobile just one week ago

从 AlarmTask 类

using System;
using System.Collections.Generic;
using System.Net;
using System.Threading.Tasks;
using Xamarin.Forms;

namespace CGSJDSportsNotification {
    public class JDMonitoring {
        class Ticket {
            string owner;
            string title;
            string store;
            string lastUpdated;
            string link;

            public string ID { get; set; }
            public string Owner {
                get {
                    return owner == null ? "Nobody" : owner;
                } set {
                    owner = value.Remove(0, value.IndexOf('(') + 1).Replace(")", "");
                }
            }
            public string Title { 
                get {
                    return title;
                } set {
                    if (value.StartsWith("(P"))
                        title = value.Remove(0, value.IndexOf(')') + 2);
                }
            }
            public string Status { get; set; }
            public string Store { 
                get {
                    return store;
                } set {
                    store = value.Replace(@"\u003C", "").Replace(">", "");
                } 
            }
            public string LastUpdated { 
                get {
                    return lastUpdated;
                } set {
                    string v;

                    int time = Convert.ToInt32(System.Text.RegularExpressions.Regex.Replace(value, @"[^\d]+", ""));

                    // Convert to minutes
                    if (value.Contains("hours"))
                        time *= 60;

                    v = time.ToString();

                    if (value.Contains("seconds"))
                        v = v.Insert(v.Length, " sec. ago");
                    else
                        v = v.Insert(v.Length, " min. ago");

                    lastUpdated = v;
                } 
            }
            public string Link { 
                get {
                    return link;
                } set {
                    link = "https://support.jdplc.com/" + value;
                } 
            }
        }

        public JDMonitoring() {
            WB.Source = JDQueueMainUrl;
            WB.Navigated += new EventHandler<WebNavigatedEventArgs>(OnNavigate);
        }

        IForegroundService FgService { get { return DependencyService.Get<IForegroundService>(); } }

        WebView WB { get; } = MainPage.UI.MonitoringWebView;
        string JDQueueMainUrl { get; } = "https://support.jdplc.com/rt4/Search/Results.html?Format=%27%3Cb%3E%3Ca%20href%3D%22__WebPath__%2FTicket%2FDisplay.html%3Fid%3D__id__%22%3E__id__%3C%2Fa%3E%3C%2Fb%3E%2FTITLE%3A%23%27%2C%0A%27%3Cb%3E%3Ca%20href%3D%22__WebPath__%2FTicket%2FDisplay.html%3Fid%3D__id__%22%3E__Subject__%3C%2Fa%3E%3C%2Fb%3E%2FTITLE%3ASubject%27%2C%0AStatus%2C%0AQueueName%2C%0AOwner%2C%0APriority%2C%0A%27__NEWLINE__%27%2C%0A%27__NBSP__%27%2C%0A%27%3Csmall%3E__Requestors__%3C%2Fsmall%3E%27%2C%0A%27%3Csmall%3E__CreatedRelative__%3C%2Fsmall%3E%27%2C%0A%27%3Csmall%3E__ToldRelative__%3C%2Fsmall%3E%27%2C%0A%27%3Csmall%3E__LastUpdatedRelative__%3C%2Fsmall%3E%27%2C%0A%27%3Csmall%3E__TimeLeft__%3C%2Fsmall%3E%27&Order=DESC%7CASC%7CASC%7CASC&OrderBy=LastUpdated%7C%7C%7C&Query=Queue%20%3D%20%27Service%20Desk%20-%20CGS%27%20AND%20(%20%20Status%20%3D%20%27new%27%20OR%20Status%20%3D%20%27open%27%20OR%20Status%20%3D%20%27stalled%27%20OR%20Status%20%3D%20%27deferred%27%20OR%20Status%20%3D%20%27open%20-%20awaiting%20requestor%27%20OR%20Status%20%3D%20%27open%20-%20awaiting%20third%20party%27%20)&RowsPerPage=0&SavedChartSearchId=new&SavedSearchId=new";
        bool MonitoringIsInProgress { get; set; } = false;

        public bool IsConnectionAvailable {
            get {
                try {
                    using (new WebClient().OpenRead("http://google.com/generate_204"))
                        return true;
                } catch {
                    return false;
                }
            }
        }

        async Task<bool> IsOnLoginPage() {
            if (await WB.EvaluateJavaScriptAsync("document.getElementsByClassName('left')[0].innerText") != null)
                return true;

            return false;
        }

        async Task<bool> Login() {
            await WB.EvaluateJavaScriptAsync($"document.getElementsByName('user')[0].value = '{UserSettings.SecureEntries.Get("rtUser")}'");
            await WB.EvaluateJavaScriptAsync($"document.getElementsByName('pass')[0].value = '{UserSettings.SecureEntries.Get("rtPass")}'");

            await WB.EvaluateJavaScriptAsync("document.getElementsByClassName('button')[0].click()");

            await Task.Delay(1000);

            // Checks for wrong credentials error
            if (await WB.EvaluateJavaScriptAsync("document.getElementsByClassName('action-results')[0].innerText") == null)
                return true;

            return false;
        }

        async Task<List<Ticket>> GetTickets() {
            List<Ticket> tkts = new List<Ticket>();

            // Queue tkts index (multiple of 2)
            int index = 2;

            // Iterates all the queue
            while (await WB.EvaluateJavaScriptAsync($"document.getElementsByClassName('ticket-list collection-as-table')[0].getElementsByTagName('tbody')[0].getElementsByTagName('tr')[{index}].innerText") != null) {
                Ticket tkt = new Ticket();

                tkt.LastUpdated = await WB.EvaluateJavaScriptAsync($"document.getElementsByClassName('ticket-list collection-as-table')[0].getElementsByTagName('tbody')[0].getElementsByTagName('tr')[{index + 1}].getElementsByTagName('td')[4].innerText");

                // Gets only the tkts which are not older than the value selected by the user
                if (Convert.ToInt32(System.Text.RegularExpressions.Regex.Replace(tkt.LastUpdated, @"[^\d]+", "")) > Convert.ToInt32(UserSettings.Entries.Get("searchTimeframe")))
                    break;

                tkt.ID     = await WB.EvaluateJavaScriptAsync($"document.getElementsByClassName('ticket-list collection-as-table')[0].getElementsByTagName('tbody')[0].getElementsByTagName('tr')[{index}].getElementsByTagName('td')[0].innerText");
                tkt.Owner  = await WB.EvaluateJavaScriptAsync($"document.getElementsByClassName('ticket-list collection-as-table')[0].getElementsByTagName('tbody')[0].getElementsByTagName('tr')[{index}].getElementsByTagName('td')[4].innerText");
                tkt.Title  = await WB.EvaluateJavaScriptAsync($"document.getElementsByClassName('ticket-list collection-as-table')[0].getElementsByTagName('tbody')[0].getElementsByTagName('tr')[{index}].getElementsByTagName('td')[1].innerText");
                tkt.Status = await WB.EvaluateJavaScriptAsync($"document.getElementsByClassName('ticket-list collection-as-table')[0].getElementsByTagName('tbody')[0].getElementsByTagName('tr')[{index}].getElementsByTagName('td')[2].innerText");
                tkt.Store  = await WB.EvaluateJavaScriptAsync($"document.getElementsByClassName('ticket-list collection-as-table')[0].getElementsByTagName('tbody')[0].getElementsByTagName('tr')[{index + 1}].getElementsByTagName('td')[1].innerText");
                tkt.Link   = await WB.EvaluateJavaScriptAsync($"document.getElementsByClassName('ticket-list collection-as-table')[0].getElementsByTagName('tbody')[0].getElementsByTagName('tr')[{index}].getElementsByTagName('td')[1].getElementsByTagName('a')[0].getAttribute('href')");

                tkts.Add(tkt);
                index += 2;
            }

            return tkts;
        }

        //async Task<string> QueueGetTkt

        async void OnNavigate(object sender, WebNavigatedEventArgs args) {
            if (MonitoringIsInProgress)
                return;

            if (IsConnectionAvailable) {
                if (await IsOnLoginPage()) {
                    if (await Login() == false) {
                        // If the log-in failed we can't proceed
                        MonitoringIsInProgress = false;

                        FgService.NotificationNewTicket("Log-in failed!", "Please check your credentials");

                        // Used to avoid an infinite loop of OnNavigate method calls
                        WB.Source = "about:blank";
                        return;
                    }
                }

                // Main core of the monitoring
                List<Ticket> tkts = await GetTickets();

                if (tkts.Count > 0) {
                    foreach(Ticket t in tkts) {
                        // Looks only after the tkts with the country selected by the user (and if it was selected by the user, also for the tkts without a visible country)

                        // Firstly we look in the title
                        if (t.Title.Contains(MainPage.UI.CountryPicker.SelectedItem.ToString())) {
                            FgService.NotificationNewTicket($"[{t.ID}] {t.LastUpdated}",
                                $"{t.Title}\r\n\r\n" +
                                $"Status:             {t.Status}\r\n" +
                                $"Owner:             {t.Owner}\r\n" +
                                $"Last updated: {t.LastUpdated}");

                            break;
                        }
                    }
                }
            }


            MonitoringIsInProgress = false;
        }
    }
}

AlarmTask 类

using Android.App;
using Android.Content;
using Android.Support.V4.App;

namespace CGSJDSportsNotification.Droid {
    [BroadcastReceiver(Enabled = true, Exported = true, DirectBootAware = true)]
    [IntentFilter(new string[] { Intent.ActionBootCompleted, Intent.ActionLockedBootCompleted, "android.intent.action.QUICKBOOT_POWERON", "com.htc.intent.action.QUICKBOOT_POWERON" }, Priority = (int)IntentFilterPriority.HighPriority)]
    public class AlarmTask : BroadcastReceiver {
        IAlarm _MainActivity { get { return Xamarin.Forms.DependencyService.Get<IAlarm>(); } }

        public override void OnReceive(Context context, Intent intent) {
            if (intent.Action != null) {
                if (intent.Action.Equals(Intent.ActionBootCompleted)) {
                    // Starts the app after reboot
                    var serviceIntent = new Intent(context, typeof(MainActivity));
                    serviceIntent.AddFlags(ActivityFlags.NewTask);
                    context.StartActivity(serviceIntent);

                    Intent main = new Intent(Intent.ActionMain);
                    main.AddCategory(Intent.CategoryHome);
                    context.StartActivity(main);

                    // Does not work, app crashes on boot received
                    /*if (UserSettings.Entries.Exists("monitoringIsRunning")) {
                        if ((bool)UserSettings.Entries.Get("monitoringIsRunning"))
                            FgService.Start();
                    }*/
                }
            } else
                // Checks for new tkts on a new thread
                new JDMonitoring();
                // Restarts the alarm
                _MainActivity.AlarmStart();
        }

        // Called from JDMonitoring class
        public static void NotificationNewTicket(string title, string message, bool icoUnknownCountry = false) {
            new AlarmTask().NotificationShow(title, message, icoUnknownCountry);
        }

        void NotificationShow(string title, string message, bool icoUnknownCountry) {
            int countryFlag = Resource.Drawable.newTktUnknownCountry;

            if (icoUnknownCountry == false) {
                switch (MainPage.UI.CountryPicker.SelectedItem.ToString()) {
                    case "Italy":
                        countryFlag = Resource.Drawable.newTktItaly;
                        break;
                    case "Spain":
                        countryFlag = Resource.Drawable.newTktSpain;
                        break;
                    case "Germany":
                        countryFlag = Resource.Drawable.newTktGermany;
                        break;
                    case "Portugal":
                        countryFlag = Resource.Drawable.newTktPortugal;
                        break;
                }
            }

            var _intent = new Intent(Application.Context, typeof(MainActivity));
            _intent.AddFlags(ActivityFlags.ClearTop);
            _intent.PutExtra("jdqueue_notification", "extra");
            var pendingIntent = PendingIntent.GetActivity(Application.Context, 0, _intent, PendingIntentFlags.OneShot);


            NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(Application.Context, "newTktNotification_channel")
                    .SetVisibility((int)NotificationVisibility.Public)
                    .SetPriority((int)NotificationPriority.High)
                    .SetDefaults((int)NotificationDefaults.Sound | (int)NotificationDefaults.Vibrate | (int)NotificationDefaults.Lights)

                    .SetSmallIcon(Resource.Drawable.newTktNotification)
                    .SetLargeIcon(Android.Graphics.BitmapFactory.DecodeResource(Application.Context.Resources, countryFlag))

                    .SetSubText("Click to check the queue")
                    .SetStyle(new NotificationCompat.BigTextStyle()
                        .SetBigContentTitle("New ticket available!")
                        .BigText(message))
                    .SetContentText(title)


                    .SetAutoCancel(true)
                    .SetContentIntent(pendingIntent);

            NotificationManagerCompat.From(Application.Context).Notify(0, notificationBuilder.Build());
        }
    }
}

和 ForegroundService 类，该类负责首次触发警报

And the ForegroundService class which is responsible to trigger for the first time the alarm

using Android.App;
using Android.Content;
using Android.OS;

namespace CGSJDSportsNotification.Droid {
    [Service]
    class ForegroundService : Service {
        IAlarm _MainActivity { get { return Xamarin.Forms.DependencyService.Get<IAlarm>(); } }

        public override IBinder OnBind(Intent intent) { return null; }

        public override StartCommandResult OnStartCommand(Intent intent, StartCommandFlags flags, int startId) {
            // Starts the Foreground Service and the notification channel
            StartForeground(9869, new ForegroundServiceNotification().ReturnNotif());

            Android.Widget.Toast.MakeText(Application.Context, "JD Queue - Monitoring started!", Android.Widget.ToastLength.Long).Show();

            _MainActivity.AlarmStart();

            return StartCommandResult.Sticky;
        }

        public override void OnDestroy() {
            Android.Widget.Toast.MakeText(Application.Context, "JD Queue - Monitoring stopped!", Android.Widget.ToastLength.Long).Show();

            _MainActivity.AlarmStop();

            UserSettings.Entries.AddOrEdit("monitoringIsRunning", false);
            UserSettings.Entries.AddOrEdit("monitoringStopPending", false, false);

            base.OnDestroy();
        }

        public override bool StopService(Intent name) {
            return base.StopService(name);
        }
    }
}

谢谢！

Thank you!

推荐答案

[更好的最终解决方案]
几个小时后，我发现了 Android WebView ，它确实满足了我的需求(我正在开发此应用仅适用于Android)

我已经编写了此浏览器帮助程序类

[BETTER-FINAL-SOLUTION]
After several hours I've discovered Android WebView which does exactly what I need (I'm developing this app only for Android)

I've written this Browser helper class

class Browser {
    public Android.Webkit.WebView WB;
    static string JSResult;

    public class CustomWebViewClient : WebViewClient {
        public event EventHandler<bool> OnPageLoaded;

        public override void OnPageFinished(Android.Webkit.WebView view, string url) {
            OnPageLoaded?.Invoke(this, true);
        }
    }

    public Browser(CustomWebViewClient wc, string url = "") {
        WB = new Android.Webkit.WebView(Android.App.Application.Context);
        WB.Settings.JavaScriptEnabled = true;


        WB.SetWebViewClient(wc);
        WB.LoadUrl(url);
    }

    public string EvalJS(string js) {
        JSInterface jsi = new JSInterface();

        WB.EvaluateJavascript($"javascript:(function() {{ return {js}; }})()", jsi);

        return JSResult;
    }

    class JSInterface : Java.Lang.Object, IValueCallback {
        public void OnReceiveValue(Java.Lang.Object value) {
            JSResult = value.ToString();
        }
    }
}

改进了异步回调的JS返回功能(因此JS返回值将总是 传递).

感谢 ChristineZuckerman

Improved the JS returning function with async callbacks (so the JS return value will be always delivered).

Credits to ChristineZuckerman

class Browser {
    public Android.Webkit.WebView WB;

    public class CustomWebViewClient : WebViewClient {
        public event EventHandler<bool> OnPageLoaded;

        public override void OnPageFinished(Android.Webkit.WebView view, string url) {
            OnPageLoaded?.Invoke(this, true);
        }
    }

    public Browser(CustomWebViewClient wc, string url = "") {
        WB = new Android.Webkit.WebView(Android.App.Application.Context);
        WB.ClearCache(true);
        WB.Settings.JavaScriptEnabled = true;
        WB.Settings.CacheMode = CacheModes.NoCache;
        WB.Settings.DomStorageEnabled = true;
        WB.Settings.SetAppCacheEnabled(false);
        WB.Settings.UserAgentString = "Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.224 Safari/534.10";
        WB.LoadUrl(url);

        WB.SetWebViewClient(wc);
    }

    public async Task<string> EvalJS(string js, bool returnNullObjectWhenNull = true) {
        string JSResult = "";
        ManualResetEvent reset = new ManualResetEvent(false);

        Device.BeginInvokeOnMainThread(() => {
            WB?.EvaluateJavascript($"javascript:(function() {{ return {js}; }})()", new JSInterface((r) => {
                JSResult = r;
                reset.Set();
            }));
        });

        await Task.Run(() => { reset.WaitOne(); });
        return JSResult == "null" ? returnNullObjectWhenNull ? null : "null" : JSResult;
    }

    class JSInterface : Java.Lang.Object, IValueCallback {
        private Action<string> _callback;

        public JSInterface(Action<string> callback) {
            _callback = callback;
        }

        public void OnReceiveValue(Java.Lang.Object value) {
            string v = value.ToString();

            if (v.StartsWith('"') && v.EndsWith('"'))
                v = v.Remove(0, 1).Remove(v.Length - 2, 1);

            _callback?.Invoke(v);
        }
    }
}

示例:

Example:

Browser.CustomWebViewClient wc = new Browser.CustomWebViewClient();
wc.OnPageLoaded += BrowserOnPageLoad;

Browser browser = new Browser(wc, "https://www.google.com/");

void BrowserOnPageLoad(object sender, bool e) {
    string test = browser.EvalJS("document.getElementsByClassName('Q8LRLc')[0].innerText");

    // 'test' will contain the value returned from the JS script
    // You can acces the real WebView object by using
    // browser.WB
}

// OR WITH THE NEW RETURNING FUNCTION

async void BrowserOnPageLoad(object sender, bool e) {
    string test = await browser.EvalJS("document.getElementsByClassName('Q8LRLc')[0].innerText");

    // 'test' will contain the value returned from the JS script
    // You can acces the real WebView object by using
    // browser.WB
}

[最终解决方案]
最后，我找到了一种简单有效的WebView替代方法.
现在，我正在使用 SimpleBroswer ，效果很好！

[FINAL-SOLUTION]
Finally I've found an easy and efficient alternative to WebView.
Now I'm using SimpleBroswer and works great!

[半自动解决方案]
好了，我已经写了一个解决方法，但是我不太喜欢这个主意，所以，如果您知道更好的方法，请告诉我.

[SEMI-SOLUTION]
Alright, I've written a workaround but I don't really like this idea, so please, if you know a better method let me know.

以下解决方法:

Below my workaround:

在我的 ForegroundServiceHelper 界面中，我添加了一种方法来检查 MainActivity (呈现WebView的位置)是否可见，如果看不到，则将显示MainActivity并立即将其隐藏起来.
该应用将从最近使用的应用中删除

In my ForegroundServiceHelper interface I've added a method to check if the MainActivity (where the WebView it's rendered) is visible or not, if isn't visible the MainActivity will be shown and immediately will be hidden back.
And the app will be removed from the last used applications

我的 ForegroundServiceHelper 界面中的方法

Method inside my ForegroundServiceHelper Interface

public void InitBackgroundWebView() {
    if ((bool)SharedSettings.Entries.Get("MainPage.IsVisible") == false) {
        // Shows the activity
        Intent serviceIntent = new Intent(context, typeof(MainActivity));
        serviceIntent.AddFlags(ActivityFlags.NewTask);
        context.StartActivity(serviceIntent);
        // And immediately hides it back
        Intent main = new Intent(Intent.ActionMain);
        main.AddFlags(ActivityFlags.NewTask);
        main.AddCategory(Intent.CategoryHome);
        context.StartActivity(main);
        // Removes from the last app used
        ActivityManager am = (new ContextWrapper(Android.App.Application.Context)).GetSystemService(Context.ActivityService).JavaCast<ActivityManager>();
        if (am != null) {
            System.Collections.Generic.IList<ActivityManager.AppTask> tasks = am.AppTasks;
            if (tasks != null && tasks.Count > 0) {
                tasks[0].SetExcludeFromRecents(true);
            }
        }
    }
}

SharedSettings 类是围绕 App.Current.Properties 字典

The SharedSettings class is an helper class wrapped around the App.Current.Properties Dictionary

在 OnAppearing 和 OnDisappearing 回调中，我将共享值设置为true/false

And in the OnAppearing and OnDisappearing callbacks I set the shared values to true/false

仅当用户位于主页上时，此解决方法才有效，因此我需要找到其他解决方案...

This workaround works only if the user is on the homepage, so I need to find an another solution...

这篇关于WebView即使应用处于后台/关闭状态(前台服务处于活动状态)如何运行的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！