Android的Service总结

参考链接：http://www.cnblogs.com/lwbqqyumidi/p/4181185.html

  Android上经常会碰到Service，用到的都比较零散，今天比较全面的了解了下。

  Service也是组件之一，如需使用，需要在清单文件中注册。代码如下：
  <service
    android:exported=["true" | "false"]
    android:icon="drawable resource"
    android:name="string"
    android:process="string" >
    . . .
  </service>
  上面是用到较多的几个属性，name为服务类，process为进程名。exported是否允许远程调用。

下面是简单的实现service类：
import android.app.Service;
import android.content.Intent;
import android.os.Handler;
import android.os.IBinder;
import android.os.Message;
import android.os.Messenger;
import android.os.RemoteException;
import android.util.Log;


public class MyService extends Service {

    public static final int MSG_SEND_TO_SERVER = 1;
    public static final int MSG_SEND_TO_CLIENT = 2;

    private Messenger mClientMessenger;
    private Messenger mServerMessenger = new Messenger(new ServerHandler());

    private static int mark =1;

    @Override
    public IBinder onBind(Intent intent) {
        return mServerMessenger.getBinder();
    }

    class ServerHandler extends Handler {

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case MSG_SEND_TO_SERVER:
                    mClientMessenger = msg.replyTo;
                    Message toClientMsg = Message.obtain(null, MSG_SEND_TO_CLIENT);
                    toClientMsg.obj = "来自Service:" + mark;
                    try {
                        mClientMessenger.send(toClientMsg);
                    } catch (RemoteException e) {
                        e.printStackTrace();
                    }
                    mark++;
                    break;
                default:
                    super.handleMessage(msg);
            }
        }
    }

    @Override
    public boolean onUnbind(Intent intent) {
        return super.onUnbind(intent);
    }

    @Override
    public void onDestroy() {
        Log.e("123","onDestroy");
        super.onDestroy();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        return START_STICKY;
    }
}

Activity调用service简单代码如下:
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Handler;
import android.os.IBinder;
import android.os.Message;
import android.os.Messenger;
import android.os.RemoteException;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private TextView tvRecord;
    private Button btnBindService;
    private Button btnStartService;
    private Button btnSend;
    private Button btnUnBindService;
    private Button btnStopService;

    private ServiceConnection sc = new MyServiceConnnect();
    private boolean isConnnect =false;


    private Messenger mServerMessenger;
    private Handler mClientHandler = new MyClientHandler();
    private Messenger mClientMessenger = new Messenger(mClientHandler);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        findView();
        setListener();
    }

    private void setListener(){
        btnBindService.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, MyService.class);
                bindService(intent, sc, Context.BIND_AUTO_CREATE);
            }
        });
        btnStartService.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, MyService.class);
                startService(intent);
            }
        });
        btnSend.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                send();
            }
        });
        btnStopService.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, MyService.class);
                stopService(intent);
            }
        });
        btnUnBindService.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(isConnnect) {
                    unbindService(sc);
                    isConnnect = false;
                }
            }
        });
    }

    private void send(){
        if (!isConnnect){
            return;
        }
        Message msg = Message.obtain(null, MyService.MSG_SEND_TO_SERVER);
        msg.replyTo = mClientMessenger;
        try {
            mServerMessenger.send(msg);
        } catch (RemoteException e) {
            e.printStackTrace();
        }
    }

    private void findView(){
        tvRecord = (TextView)findViewById(R.id.tv_record);
        btnBindService = (Button) findViewById(R.id.btn_bind);
        btnStartService = (Button)findViewById(R.id.btn_start);
        btnSend = (Button)findViewById(R.id.btn_send);
        btnStopService = (Button)findViewById(R.id.btn_stop);
        btnUnBindService = (Button)findViewById(R.id.btn_unbind);
    }

    class MyClientHandler extends Handler{
        @Override
        public void handleMessage(Message msg) {
            if (msg.what == MyService.MSG_SEND_TO_CLIENT) {
                String obj = (String)msg.obj;
                tvRecord.setText(obj);
            }
        }
    }

    class MyServiceConnnect implements ServiceConnection{
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            mServerMessenger = new Messenger(service);
            isConnnect =true;
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            isConnnect =false;
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();

    }
}


  一般启动服务有两方法：startService和bindService。
  startService比较简单，通过stopService结束。当服务已经启动，则不会调用oncreate方法，直接调用onStartCommand。startCommand的返回值意义如下：
START_NOT_STICKY：当Service因为内存不足而被系统kill后，接下来未来的某个时间内，即使系统内存足够可用，系统也不会尝试重新创建此Service。除非程序中Client明确再次调用startService(...)启动此Service。

START_STICKY：当Service因为内存不足而被系统kill后，接下来未来的某个时间内，当系统内存足够可用的情况下，系统将会尝试重新创建此Service，一旦创建成功后将回调onStartCommand(...)方法，但其中的Intent将是null，pendingintent除外。

START_REDELIVER_INTENT：与START_STICKY唯一不同的是，回调onStartCommand(...)方法时，其中的Intent将是非空，将是最后一次调用startService(...)中的intent。

START_STICKY_COMPATIBILITY：compatibility version of {@link #START_STICKY} that does not guarantee that {@link #onStartCommand} will be called again after being killed。此值一般不会使用，所以注意前面三种情形就好。

  bindService也可启动服务，可通过unbindService结束，此方法可通过接口，通过信使通信。具体代码如上。如通过bindservice启动的服务，需关闭所有的依赖才可结束服务。