android中service启动后台程序

Service是Android中一个类，它是Android四大组件之一，使用Service可以在后台执行长时间的操作（ perform long-running operations in the background ），Service并不与用户产生UI交互。其他的应用组件可以启动Service，即便用户切换了其他应用，启动的Service仍可在后台运行。一个组件可以与Service绑定并与之交互，甚至是跨进程通信（IPC）。例如，一个Service可以在后台执行网络请求、播放音乐、执行文件读写操作或者与 content provider交互 等。

ps：附上一个service组件介绍的网站：https://blog.csdn.net/scott2017/article/details/51505801

下面是一个音乐后台播放的例子：

1.Activity类

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

/**
 * Created by cj on 2018/3/28.
 */

public class ServiceDemo extends Activity implements View.OnClickListener{

    private static final String TAG = "ServiceDemo";
    Button buttonStart, buttonStop;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.servicedemo);

        buttonStart = (Button) findViewById(R.id.buttonStart);
        buttonStop = (Button) findViewById(R.id.buttonStop);

        buttonStart.setOnClickListener(this);
        buttonStop.setOnClickListener(this);
    }

    public void onClick(View src) {
        switch (src.getId()) {
            case R.id.buttonStart:
                Log.i(TAG, "onClick: starting service");
                startService(new Intent(this, MyService.class));
                break;
            case R.id.buttonStop:
                Log.i(TAG, "onClick: stopping service");
                stopService(new Intent(this, MyService.class));
                break;
        }
    }

}
2.Service子类：

import android.app.Notification;
import android.app.Service;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.Build;
import android.os.Debug;
import android.os.IBinder;
import android.support.annotation.Nullable;
import android.util.Log;
import android.widget.Toast;

/**
 * Created by cj on 2018/3/28.
 */

public class MyService extends Service {

    private static final String TAG = "MyService";
    private final static int GRAY_SERVICE_ID = 1001;
    MediaPlayer player;

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    @Override
    public void onCreate() {
        Toast.makeText(this,"MyService Created",Toast.LENGTH_SHORT).show();
        Log.i(TAG,"oncreated");
        player = MediaPlayer.create(this,R.raw.huanghun);  //此处的R.raw.huanghun为要播放的音乐资源。在res文件夹下创建raw目录，huanghun.mp3为音乐资源，放到创建好的raw文件夹下
        player.setLooping(false);
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        //sdk小于18时启动一个状态栏通知
        if(Build.VERSION.SDK_INT<18){
            startForeground(GRAY_SERVICE_ID,new Notification());
        }else{
            //sdk大于18 时启动一个状态栏通知
            Intent intent1 = new Intent(this,GrayInnerService.class);
            startService(intent1);
            startForeground(GRAY_SERVICE_ID,new Notification());
        }
        return super.onStartCommand(intent, flags, startId);
    }

    //给API >= 18 的平台上做灰色保护手段
    public class GrayInnerService extends Service {
        @Override
        public IBinder onBind(Intent intent) {
            return null;
        }


        @Override
        public int onStartCommand(Intent intent, int flags, int startId) {
            startForeground(GRAY_SERVICE_ID, new Notification());
            stopForeground(true);
            stopSelf();

            return super.onStartCommand(intent, flags, startId);
        }
    }

    @Override
    public void onDestroy() {
        Toast.makeText(this, "My Service Stoped", Toast.LENGTH_LONG).show();
        Log.i(TAG, "onDestroy");
        player.stop();
    }

    @Override
    public void onStart(Intent intent, int startId) {
        Toast.makeText(this, "My Service Start", Toast.LENGTH_LONG).show();
        Log.i(TAG, "onStart");
        player.start();
    }
}
3.布局文件

<?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"
    android:gravity="center">
    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" android:text="@string/servicesdemo" android:gravity="center" android:textSize="20sp" android:padding="20dp"/>
    <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/buttonStart" android:text="@string/start"></Button>
    <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/stop" android:id="@+id/buttonStop"></Button>
</LinearLayout>

4.String.xml文件

<resources>
    <string name="app_name">update</string>  //此处为运用程序的名称，一般项目创建时自带
    <string name="start">播放</string>
    <string name="stop">停止</string>
    <string name="servicesdemo">Service Demo</string>
</resources>
5.manifest.xml文件中配置

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

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <service android:enabled="true" android:name=".MyService"/>  //此处配置，name为service的子类。
</application>