【Android】17.3 Activity与StartedService的绑定

分类:C#、Android、VS2015;

创建日期:2016-03-03

一、简介

除了上一节介绍的基本绑定以外,你还可以创建一个同时支持started和bound的服务。也就是说,服务可以通过调用 StartService() 来启动,这会使它一直保持运行,同时它也允许客户端通过调用BindService() 来与之绑定。

虽然你通常应该要实现 OnBind() 或 OnStartCommand() 中的一个,但有时需要同时实现两者。比如,音乐播放器的服务也许就需要同时实现后台运行和支持绑定。这样,activity就可以启动服务来播放音乐,并且音乐会一直播放下去,即使用户离开该应用程序也没关系,这个activity可以绑定播放服务来重新获得播放控制权。

另外,如果你的服务是started和bound的,那么服务启动后,系统将不会在所有客户端解除绑定时销毁它。取而代之的是,你必须通过调用StopSelf() 或 StopService() 显式终止此服务。

服务只在为绑定的应用程序组件工作时才会存活,因此,只要没有组件绑定到服务,系统就会自动销毁服务(你不需要像started服务中那样通过OnStartCommand()来终止一个bound服务)。

一旦OnBind方法返回绑定的实例,Android就会引发实现IServiceConnection接口的对象的ServiceConnected事件,然后,客户端就可以通过Binder引用它。

多个客户端可以同时连接到同一个服务上。不过,只有在第一个客户端绑定时,系统才会调用服务的 OnBind() 方法来获取 IBinder 。然后,系统会向后续请求绑定的客户端传送这同一个 IBinder ,而不再调用 OnBind() 。当最后一个客户端解除绑定后,系统会自动销毁服务(除非服务是同时通过 StartService() 启动的)。

二、示例2运行截图

该例子演示如何绑定到一个started服务。

单击【启动服务】按钮后,就会在左上角出现一个通知图标,下拉展开该图标,就可以看到来自服务的通知信息。

image  image

单击【调用服务中提供的方法】按钮,会显示调用服务中对应方法返回的结果,单击【停止服务】按钮,左上角的通知图标也会同时消失。

三、主要设计步骤

1、添加ch1702_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <Button
        android:id="@+id/ch1702_startService"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="启动服务" />
    <Button
        android:id="@+id/ch1702_callService"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="调用服务中提供的方法" />
    <Button
        android:id="@+id/ch1702_stopService"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="停止服务" />
</LinearLayout>

2、添加ch1702Service.cs

using Android.App;
using Android.Content;
using Android.OS;
using Android.Widget;
using System.Threading;

namespace MyDemos.SrcDemos
{
    [Service]
    [IntentFilter(new string[] { action })]
    public class ch1702Service : Service
    {
        public const string action = "ServiceDemo.ch1702Service";
        ch1702ServiceBinder binder;

        public override StartCommandResult OnStartCommand(Intent intent, StartCommandFlags flags, int startId)
        {
            Notification notification = GetNotification();
            //启动前台任务
            StartForeground((int)NotificationFlags.ForegroundService, notification);

            var t = new Thread(() =>
            {
                //发送通知
                var m = (NotificationManager)GetSystemService(NotificationService);
                m.Notify((int)NotificationFlags.ForegroundService, notification);

                Thread.Sleep(50000);  //延时50秒模拟长时间运行的服务

                //停止前台任务
                StopForeground(true);
                //停止后台服务
                StopSelf();
            });
            t.Start();
            return StartCommandResult.NotSticky;
        }

        private Notification GetNotification()
        {
            var pendingIntent = PendingIntent.GetActivity(this,
                (int)NotificationFlags.ForegroundService,
                new Intent(this, typeof(MainActivity)),
                PendingIntentFlags.UpdateCurrent);
            Notification.Builder builder = new Notification.Builder(this)
                .SetContentTitle("来自ch1702Service的通知")
                .SetContentText("正在前台运行ch1702Service")
                .SetContentIntent(pendingIntent)
                .SetSmallIcon(Resource.Drawable.Icon);
            Notification notification = builder.Build();
            return notification;
        }

        public override IBinder OnBind(Android.Content.Intent intent)
        {
            binder = new ch1702ServiceBinder(this);
            return binder;
        }

        public string GetText()
        {
            return "这是来自ch1702Service的信息";
        }

        public override void OnDestroy()
        {
            var myHandler = new Handler();
            myHandler.Post(() =>
            {
                Toast.MakeText(this, "正在停止ch1702Service", ToastLength.Long).Show();
            });
            base.OnDestroy();
        }
    }

    public class ch1702ServiceBinder : Binder
    {
        ch1702Service service;

        public ch1702ServiceBinder(ch1702Service service)
        {
            this.service = service;
        }

        public ch1702Service GetMyService()
        {
            return service;
        }
    }
}

3、添加ch1702MainActivity.cs

using Android.App;
using Android.Content;
using Android.OS;
using Android.Widget;
using Android.Content.Res;

namespace MyDemos.SrcDemos
{
    [Activity(Label = "ch1702MainActivity")]
    public class ch1702MainActivity : Activity
    {
        bool isBound = false;
        bool isConfigurationChange = false;
        ch1702ServiceBinder binder;
        ch1702ServiceConnection myServiceConnection;
        Intent serviceIntent;

        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.ch1702_main);

            var start = FindViewById<Button>(Resource.Id.ch1702_startService);
            start.Click += delegate
            {
                serviceIntent = new Intent(ch1702Service.action);
                StartService(serviceIntent);
            };

            var callService = FindViewById<Button>(Resource.Id.ch1702_callService);
            callService.Click += delegate
            {
                if (isBound)
                {
                    RunOnUiThread(() =>
                    {
                        string text = binder.GetMyService().GetText();
                        Toast.MakeText(this, text, ToastLength.Short).Show();
                    });
                }
            };

            var stop = FindViewById<Button>(Resource.Id.ch1702_stopService);
            stop.Click += delegate
            {
                StopService(serviceIntent);
                if (isBound)
                {
                    UnbindService(myServiceConnection);
                    isBound = false;
                }
            };

            // 如果配置改变了(比如旋转了屏幕),则恢复连接
            if (myServiceConnection != null)
            {
                binder = myServiceConnection.Binder;
            }
        }

        protected override void OnStart()
        {
            base.OnStart();
            var myServiceIntent = new Intent(ch1702Service.action);
            myServiceConnection = new ch1702ServiceConnection(this);
            BindService(myServiceIntent, myServiceConnection, Bind.AutoCreate);
        }

        public override void OnConfigurationChanged(Configuration newConfig)
        {
            isConfigurationChange = true;
            base.OnConfigurationChanged(newConfig);
        }

        protected override void OnDestroy()
        {
            base.OnDestroy();

            if (!isConfigurationChange)
            {
                if (isBound)
                {
                    UnbindService(myServiceConnection);
                    isBound = false;
                }
            }
        }

        private class ch1702ServiceConnection : Java.Lang.Object, IServiceConnection
        {
            private ch1702MainActivity activity;
            public ch1702ServiceBinder Binder { get; private set; }

            public ch1702ServiceConnection(ch1702MainActivity activity)
            {
                this.activity = activity;
            }

            public void OnServiceConnected(ComponentName name, IBinder service)
            {
                var myServiceBinder = service as ch1702ServiceBinder;
                if (myServiceBinder != null)
                {
                    activity.binder = myServiceBinder;
                    activity.isBound = true;

                    // 即使配置发生了改变,仍保持绑定到该实例
                    Binder = myServiceBinder;
                }
            }

            public void OnServiceDisconnected(ComponentName name)
            {
                activity.isBound = false;
            }
        }
    }
}
posted @ 2016-03-03 09:11  rainmj  阅读(488)  评论(0编辑  收藏  举报