Android使用service后台更新计划任务

Service是Android的四大组件之一，这里就不再过多的去描述，下面主要实现启动应用时候利用service后台执行计划任务，退出应用后，关闭service,只存在整个应用的周期中。

首先使用service需要在manifest中的Application 中注册

  <service android:name=".WxService" android:enabled="true" android:exported="true" >
  </service>       

写一个WxService类，继承于Service,然后实现它的一些方法。

public class WxService extends Service{

    @Override
    public IBinder onBind(Intent intent) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void onCreate() {
        // TODO Auto-generated method stub
        super.onCreate();
        Timer timer = new Timer();
        timer.schedule(new Work(),0, 30000);

    }

    @Override
    public void onStart(Intent intent, int startId) {
        // TODO Auto-generated method stub
        super.onStart(intent, startId);
    }
}

在onCreate()方法中去调度计划,下面介绍一个这个Schedule类。

public void schedule(TimerTask task,
                     long delay,
                     long period)
Schedules the specified task for repeated fixed-delay execution, beginning after the specified delay. Subsequent executions take place at approximately regular intervals separated by the specified period.
In fixed-delay execution, each execution is scheduled relative to the actual execution time of the previous execution. If an execution is delayed for any reason (such as garbage collection or other background activity), subsequent executions will be delayed as well. In the long run, the frequency of execution will generally be slightly lower than the reciprocal of the specified period (assuming the system clock underlying Object.wait(long) is accurate).

Fixed-delay execution is appropriate for recurring activities that require "smoothness." In other words, it is appropriate for activities where it is more important to keep the frequency accurate in the short run than in the long run. This includes most animation tasks, such as blinking a cursor at regular intervals. It also includes tasks wherein regular activity is performed in response to human input, such as automatically repeating a character as long as a key is held down.

Parameters:
task - task to be scheduled.
delay - delay in milliseconds before task is to be executed.
period - time in milliseconds between successive task executions.
Throws:
IllegalArgumentException - if delay is negative, or delay + System.currentTimeMillis() is negative.
IllegalStateException - if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated.
说明：该方法会在指定的延时后执行任务，并且在设定的周期定时执行任务。

计划任务

 class Work extends TimerTask{

        @Override
        public void run() {
            // TODO Auto-generated method stub
        Message message = new Message();
        message.what=1;
        handler.sendMessage(message);
        }
     }

     Handler handler = new Handler()
     {

        @Override
        public void handleMessage(Message msg) {
            // TODO Auto-generated method stub
            super.handleMessage(msg);
            if(msg.what==1)
            {
                new Updata().execute();
            }
        }

     };

在Activity中启动Service

Intent i  = new Intent(context,WxService.class);
context.startService(i);

退出应用程序时候，停止服务

Intent i  = new Intent(context,WxService.class);
context.stopService(i);