Android四大组件之服务-Service 原理和应用开发详解

一、Android 服务简介

Service是android 系统中的四大组件之一（Activity、Service、BroadcastReceiver、ContentProvider），它跟Activity的级别差不多，但不能自己运行只能后台运行，并且可以和其他组件进行交互。service可以在很多场合的应用中使用，比如播放多媒体的时候用户启动了其他Activity这个时候程序要在后台继续播放，比如检测SD卡上文件的变化，再或者在后台记录你地理信息位置的改变等等，总之服务总是藏在后台的。

Service的启动有两种方式：context.startService() 和 context.bindService()

二、原理和流程

1.创建前台服务，只需要提供一个通知栏图标并且调用startForeground即可。

2.想让服务做自己的想做的事情，也比较简单，只需要在onCreate或者onStartConmand的时候new一个Thread即可

3.如果Activity等UI想要和服务通信、调用服务提供的方法，怎么办呢？这时候就需要用到Binder了：只需要在onBind的时候返回一个IBinder对象，通过该对象可以获取当前Service的对象引用，这样就可以操作服务所提供的方法了，那如何在Service操作Acitivty呢？

有了Service引用，这个时候只需要在Service中给Activity开放设置回调接口即可。

4.当然了，服务需要在Manifest.xml中进行配置声明：

 <service android:name="com.czm.servicetest.MyService" >
  </service>

三、实例：MyService.java

package com.czm.servicetest;

import android.app.Service;
import android.content.Intent;
import android.os.Binder;
import android.os.IBinder;
import android.util.Log;
/**
 * The Service Example
 * @author caizhiming
 *
 */
public class MyService extends Service{

    IBinder mBinder = new MyBinder();
    private int mCount = 0;
    public boolean mIsStop = false;
    
    // get the instance of MyService
    public class MyBinder extends Binder{
        MyService getService(){
            return MyService.this;
        }
    }
    
    public void setData(int data){
        mCount = data;
    }
    public int getData(){
        return mCount;
    }
    @Override
    public void onCreate() {
        // TODO Auto-generated method stub
        super.onCreate();
        Thread thread = new Thread(null, new ServiceWorker(), "ServiceWorker");
        thread.start();
    }
    @Override
    public IBinder onBind(Intent intent) {
        // TODO Auto-generated method stub
        Log.v("czm","onBind()-service is started");
        return mBinder;
    }
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        // TODO Auto-generated method stub
        Log.v("czm","onStartCommand()-service is started");
        return super.onStartCommand(intent, flags, startId);
    }
    //The Service work's thread
    class ServiceWorker implements Runnable{

        @Override
        public void run() {
            // TODO Auto-generated method stub
            while(!mIsStop){
                Log.v("czm","ServiceWorker: mCount="+mCount);
                mCount ++;
                if(mCount >=  10000){
                    mCount  = 0;
                }
                if(mCount %5 == 0){
                    mListener.onCallback();
                }
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            
        }
    }
    //The callback listener to operate UI such as Activity
    private OnUICallbackListener mListener;
    public void setListener(OnUICallbackListener listener){
        mListener = listener;
    }
    public interface OnUICallbackListener{
        void onCallback();
    }

    
}

四、如何使用服务-MyService？

package com.czm.servicetest;
import com.czm.servicetest.MyService.MyBinder;
import com.czm.servicetest.MyService.OnUICallbackListener;

import android.app.Activity;
import android.content.ComponentName;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.Handler;
import android.os.IBinder;
import android.os.Message;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;


public class MainActivity extends Activity implements OnUICallbackListener{
    private Button mBtnStart;
    private Button mBtnChange;
    private Button mBtnStop;
    private TextView mTvResult;
    
    private MyService mMyService;
    Intent serviceIntent;
    
    private Handler mHandler = new Handler(){
        public void handleMessage(Message msg) {
            mTvResult.setText(String.valueOf(mMyService.getData()));
            mHandler.sendEmptyMessageDelayed(0, 1000);
        };
    };
    
    private ServiceConnection mServiceConnection = new ServiceConnection() {
        
        @Override
        public void onServiceDisconnected(ComponentName name) {
            // TODO Auto-generated method stub
            Log.v("czm","onServiceDisconnected()");
        }
        
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            // TODO Auto-generated method stub
            Log.v("czm","onServiceConnected()");
            MyBinder binder = (MyBinder) service;
            mMyService = binder.getService();
            mMyService.setListener(MainActivity.this);
            mHandler.sendEmptyMessageDelayed(0, 0);
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mBtnStart = (Button)findViewById(R.id.btn_start);
        mBtnChange = (Button)findViewById(R.id.btn_change);
        mBtnStop = (Button)findViewById(R.id.btn_stop);
        mTvResult = (TextView)findViewById(R.id.tv_result);
        
        mBtnStart.setOnClickListener(new OnClickListener() {
            
            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                //start service
                serviceIntent = new Intent(MainActivity.this,MyService.class);
                serviceIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                //bind service in order to communicate with service
                MainActivity.this.bindService(serviceIntent, mServiceConnection, BIND_AUTO_CREATE);
//                startService(serviceIntent);
            }
        });
        mBtnChange.setOnClickListener(new OnClickListener() {
            
            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                mMyService.setData(1000);
            }
        });
        mBtnStop.setOnClickListener(new OnClickListener() {
            
            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                mMyService.mIsStop = true;
                MainActivity.this.unbindService(mServiceConnection);
                stopService(serviceIntent);
            }
        });
    }
    
    /**
     * service callback 
     * @param serviceConnection
     */
    @Override
    public void onCallback() {
        // TODO Auto-generated method stub
        runOnUiThread(new Runnable() {
            
            @Override
            public void run() {
                // TODO Auto-generated method stub
                Toast.makeText(MainActivity.this, "service callback", Toast.LENGTH_SHORT).show();
            }
        });
        
    }
}

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