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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