定时器的实现

1、TimerTask

TimerTask task = new TimerTask() {        public void run() {            Message message = new Message();            message.what = 2;            handler.sendMessage(message);        }    };

/**     * 进行信息的轮询     */    private void inithttp() {        timer = new Timer(true);        timer.schedule(task, 1000 * 10, 1000 * 5); // 延时1000ms后执行，1000ms执行一次        // timer.cancel(); //退出计时器    }

2、消息推送
（1）service +Thread
在service中开启一个带有while循环的线程，使其不断的从服务器查询数据（一定时间间隔内），当发现有需要通知用户的情况下发送notification。

import org.apache.http.Header;import org.json.JSONObject;import android.app.Notification;import android.app.NotificationManager;import android.app.PendingIntent;import android.app.Service;import android.content.Context;import android.content.Intent;import android.os.IBinder;import android.widget.Toast;import com.loopj.android.http.AsyncHttpClient;import com.loopj.android.http.AsyncHttpResponseHandler;/** * * 短信推送服务类，在后台长期运行，每个一段时间就向服务器发送一次请求 * * @author jerry * */public class PushSmsService extends Service {    private MyThread myThread;    private NotificationManager manager;    private Notification notification;    private PendingIntent pi;    private AsyncHttpClient client;    private boolean flag = true;    @Override    public IBinder onBind(Intent intent) {        // TODO Auto-generated method stub        return null;    }    @Override    public void onCreate() {        System.out.println("oncreate()");        this.client = new AsyncHttpClient();        this.myThread = new MyThread();        this.myThread.start();        super.onCreate();    }    @Override    public void onDestroy() {        this.flag = false;        super.onDestroy();    }    private void notification(String content, String number, String date) {        // 获取系统的通知管理器        manager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);        notification = new Notification(R.drawable.ic_menu_compose, content,                System.currentTimeMillis());        notification.defaults = Notification.DEFAULT_ALL; // 使用默认设置，比如铃声、震动、闪灯        notification.flags = Notification.FLAG_AUTO_CANCEL; // 但用户点击消息后，消息自动在通知栏自动消失        notification.flags |= Notification.FLAG_NO_CLEAR;// 点击通知栏的删除，消息不会依然不会被删除        Intent intent = new Intent(getApplicationContext(),                ContentActivity.class);        intent.putExtra("content", content);        intent.putExtra("number", number);        intent.putExtra("date", date);        pi = PendingIntent.getActivity(getApplicationContext(), 0, intent, 0);        notification.setLatestEventInfo(getApplicationContext(), number                + "发来短信", content, pi);        // 将消息推送到状态栏        manager.notify(0, notification);    }    private class MyThread extends Thread {        @Override        public void run() {            String url = "你请求的网络地址";            while (flag) {                System.out.println("发送请求");                try {                    // 每个10秒向服务器发送一次请求                    Thread.sleep(10000);                } catch (InterruptedException e) {                    e.printStackTrace();                }                // 采用get方式向服务器发送请求                client.get(url, new AsyncHttpResponseHandler() {                    @Override                    public void onSuccess(int statusCode, Header[] headers,                            byte[] responseBody) {                        try {                            JSONObject result = new JSONObject(new String(                                    responseBody, "utf-8"));                            int state = result.getInt("state");                            // 假设偶数为未读消息                            if (state % 2 == 0) {                                String content = result.getString("content");                                String date = result.getString("date");                                String number = result.getString("number");                                notification(content, number, date);                            }                        } catch (Exception e) {                            e.printStackTrace();                        }                    }                    @Override                    public void onFailure(int statusCode, Header[] headers,                            byte[] responseBody, Throwable error) {                        Toast.makeText(getApplicationContext(), "数据请求失败", 0)                                .show();                    }                });            }        }    }}

是应用长期有一个后台程序运行，如果是一个喜欢用手机安全的用户，这个service很可能被他杀死；二是虽然service可以运行在后台，但在手机休眠的情况下线程好像是被挂起的，

（2）service+AlarmManager+Thread
AlarmManager在特定的时刻为我们广播一个指定的Intent。简单的说就是我们设定一个时间，然后在该时间到来时，AlarmManager为我们广播一个我们设定的Intent。
/////轮询工具类PollingUtils.java

public class PollingUtils {    //开启轮询服务    public static void startPollingService(Context context, int seconds, Class<?> cls,String action) {        //获取AlarmManager系统服务        AlarmManager manager = (AlarmManager) context                .getSystemService(Context.ALARM_SERVICE);        //包装需要执行Service的Intent        Intent intent = new Intent(context, cls);        intent.setAction(action);        PendingIntent pendingIntent = PendingIntent.getService(context, 0,                intent, PendingIntent.FLAG_UPDATE_CURRENT);        //触发服务的起始时间        long triggerAtTime = SystemClock.elapsedRealtime();        //使用AlarmManger的setRepeating方法设置定期执行的时间间隔（seconds秒）和需要执行的Service        manager.setRepeating(AlarmManager.ELAPSED_REALTIME, triggerAtTime,                seconds * 1000, pendingIntent);    }    //停止轮询服务    public static void stopPollingService(Context context, Class<?> cls,String action) {        AlarmManager manager = (AlarmManager) context                .getSystemService(Context.ALARM_SERVICE);        Intent intent = new Intent(context, cls);        intent.setAction(action);        PendingIntent pendingIntent = PendingIntent.getService(context, 0,                intent, PendingIntent.FLAG_UPDATE_CURRENT);        //取消正在执行的服务        manager.cancel(pendingIntent);    }}

////////
轮询任务执行PollingService.java

public class PollingService extends Service {    public static final String ACTION = "com.ryantang.service.PollingService";    private Notification mNotification;    private NotificationManager mManager;    @Override    public IBinder onBind(Intent intent) {        return null;    }    @Override    public void onCreate() {        initNotifiManager();    }    @Override    public void onStart(Intent intent, int startId) {        new PollingThread().start();    }    //初始化通知栏配置    private void initNotifiManager() {        mManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);        int icon = R.drawable.ic_launcher;        mNotification = new Notification();        mNotification.icon = icon;        mNotification.tickerText = "New Message";        mNotification.defaults |= Notification.DEFAULT_SOUND;        mNotification.flags = Notification.FLAG_AUTO_CANCEL;    }    //弹出Notification    private void showNotification() {        mNotification.when = System.currentTimeMillis();        //Navigator to the new activity when click the notification title        Intent i = new Intent(this, MessageActivity.class);        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, i,                Intent.FLAG_ACTIVITY_NEW_TASK);        mNotification.setLatestEventInfo(this,                getResources().getString(R.string.app_name), "You have new message!", pendingIntent);        mManager.notify(0, mNotification);    }    /**     * Polling thread     * 模拟向Server轮询的异步线程     * @Author Ryan     * @Create 2013-7-13 上午10:18:34     */    int count = 0;    class PollingThread extends Thread {        @Override        public void run() {            System.out.println("Polling...");            count ++;            //当计数能被5整除时弹出通知            if (count % 5 == 0) {                showNotification();                System.out.println("New message!");            }        }    }    @Override    public void onDestroy() {        super.onDestroy();        System.out.println("Service:onDestroy");    }}

/////////开启和停止PollingService

public class MainActivity extends Activity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        //Start polling service        System.out.println("Start polling service...");        PollingUtils.startPollingService(this, 5, PollingService.class, PollingService.ACTION);    }    @Override    protected void onDestroy() {        super.onDestroy();        //Stop polling service        System.out.println("Stop polling service...");        PollingUtils.stopPollingService(this, PollingService.class, PollingService.ACTION);    }}

一种是利用系统服务，一种是自己通过while循环。显然使用系统服务具有更高的稳定性，而且恰好解决了休眠状态下轮询中断的问题，因为AlarmManager是始终运行者的。