Service简介:
Service 是Android的四大组件之一,一般用于没有UI界面,长期执行的后台任务,即使程序退出时,后台任务还在执行。比如:音乐播放。
Service的误区:
1.service在UI线程中执行。
2.不可以在service中执行耗时任务,因为service是在UI线程中运行的。
3.如果需要执行后台的耗时任务,必须在Service中开启一个线程来执行。
Service的生命周期:
启动和停止Service的两种方式
1.context.startService();context.stopService().
2.context.bindService();context.unbindService().
Service使用实例1:
客户端代码如下:
package com.xjp.broadcast;import android.app.Activity;import android.content.BroadcastReceiver;import android.content.Context;import android.content.Intent;import android.content.IntentFilter;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;public class MainActivity extends Activity {private final static String action = "com.xjp.MainActivity";private TextView result;private Button startService;private Button stopService;private BroadcastReceiver broadcastReceiver = new BroadcastReceiver() {@Overridepublic void onReceive(Context context, Intent intent) {int i = intent.getIntExtra("key", 0);result.setText(i + "");}};@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);result = (TextView) findViewById(R.id.result);startService = (Button) findViewById(R.id.startService);startService.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {Intent service = new Intent(MainActivity.this, CalculationService.class);startService(service);}});stopService = (Button) findViewById(R.id.stopService);stopService.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {Intent service = new Intent(MainActivity.this, CalculationService.class);stopService(service);}});}@Overrideprotected void onResume() {super.onResume();initFilter();}@Overrideprotected void onDestroy() {super.onDestroy();unregisterReceiver(broadcastReceiver);}private void initFilter() {IntentFilter filter = new IntentFilter();filter.addAction(action);registerReceiver(broadcastReceiver, filter);}} 1.依次点击“启动服务” 和“停止服务” ,生命周期 打印结果如下:
2.点击两次 “启动服务” 打印结果如下:
这种方式可以多次启动同一个Service,并且 只有第一次才执行 onCreate。第二次之后 就只执行 onStartCommand,并且当且仅当该应用退出之后,该服务依然存在后台运行着。退出之后,在设置里面查看正在运行的应用:
服务端代码如下:
package com.xjp.broadcast;import android.app.Service;import android.content.Intent;import android.os.IBinder;import android.util.Log;/** * Description: * User: xjp * Date: 2015/5/4 * Time: 14:14 */public class CalculationService extends Service {private final static String TAG = "CalculationService";private final static String action = "com.xjp.MainActivity";private boolean quit = false;@Overridepublic IBinder onBind(Intent intent) {Log.e(TAG, "====onBind=====");return null;}@Overridepublic boolean onUnbind(Intent intent) {Log.e(TAG, "====onUnbind=====");return super.onUnbind(intent);}@Overridepublic void onCreate() {Log.e(TAG, "====onCreate=====");super.onCreate();}@Overridepublic int onStartCommand(Intent intent, int flags, int startId) {Log.e(TAG, "====onStartCommand=====");startThread();return super.onStartCommand(intent, flags, startId);}@Overridepublic void onDestroy() {Log.e(TAG, "====onDestroy=====");quit = true;super.onDestroy();}/*** 开启线程模拟耗时任务*/public void startThread() {new Thread(new Runnable() {int i = 0;@Overridepublic void run() {while (i < 200 && !quit) {try {Thread.sleep(1000);i++;Intent intent = new Intent(action);intent.putExtra("key", i);sendBroadcast(intent);} catch (InterruptedException e) {e.printStackTrace();}}}}).start();}}
Service使用实例2:
客户端代码如下:
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