之前写了两篇文章，分别是在活动中创建通知和在广播接收器中创建通知，今天再来写一篇在服务中创建通知----也就是所谓的前台service。

从Android8.0开始，只有当应用保持在前台可见状态下，service才能保证稳定运行，一旦应用进入了后台，service可能随时会被回收。所以可以考虑使用前台service，它和普通是service的最大区别就是，它一直会有一个正在运行的图标在系统的状态栏显示，下拉状态栏可以看到更详细的信息，和通知的效果很像，

其实就是在服务中创建了通知而已，点击它可以进去指定的APP活动。

先来看看效果吧

代码实现

1.MainActivity.java

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button start=findViewById(R.id.start_service);
        Button stop=findViewById(R.id.stop_service);
        start.setOnClickListener(this);
        stop.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.start_service:
                Intent startIntent=new Intent(MainActivity.this,MyService.class);
                startService(startIntent);
                break;
            case R.id.stop_service:
                Intent stopIntent =new Intent(MainActivity.this,MyService.class);
                stopService(stopIntent);
                break;
        }
    }
}

2.activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:layout_gravity="center"
    tools:context=".MainActivity">

    <Button
        android:layout_width="0dp"
        android:layout_weight="1"
        android:layout_height="wrap_content"
        android:id="@+id/start_service"
        android:text="开启服务"/>
    <Button
        android:layout_width="0dp"
        android:layout_weight="1"
        android:layout_height="wrap_content"
        android:id="@+id/stop_service"
        android:text="停止服务"/>

</LinearLayout>

3.MyService.java

public class MyService extends Service {
    public MyService() {
    }

    @Override
    public IBinder onBind(Intent intent) {
        // TODO: Return the communication channel to the service.
        throw new UnsupportedOperationException("Not yet implemented");
    }

    @Override
    public void onCreate() {
        super.onCreate();
        Log.d("MyService","onCreate");
        NotificationChannel notificationChannel = null;
        if(Build.VERSION.SDK_INT>=Build.VERSION_CODES.O){
            notificationChannel = new NotificationChannel("important", "Important", NotificationManager.IMPORTANCE_LOW);
            NotificationManager notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
            assert notificationManager != null;
            notificationManager.createNotificationChannel(notificationChannel);
        }
        Intent intent=new Intent(this,MainActivity.class);
        PendingIntent pi=PendingIntent.getActivity(this,0,intent,0);
        Notification notification=new NotificationCompat.Builder(this,"important")
                .setContentTitle("前台服务")
                .setContentText("app正在运行")
                .setWhen(System.currentTimeMillis())
                .setSmallIcon(R.mipmap.ic_launcher)
                .setContentIntent(pi)
                .build();

        startForeground(1,notification);
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.d("MyService","onStartCommand");
        return super.onStartCommand(intent, flags, startId);

    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.d("MyService","onDestroy");
    }
}

4.在manifest的​​<application​​前面添加申请前台服务权限：

<uses-permission android:name="android.permission.FOREGROUND_SERVICE" />

在 ​​<application​​里面添加注册服务代码

<service
     android:name=".MyService"
     android:enabled="true"
     android:exported="true" />

整个manifest参考：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="com.example.servicetest">
    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme"
        tools:ignore="AllowBackup,GoogleAppIndexingWarning">
        <service
            android:name=".MyService"
            android:enabled="true"
            android:exported="true" />

        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

GitHub：https://github.com/wangjinchan/ServiceTest

参考：郭霖的《第一行代码》第三版 kotlin