Android使用service後台更新計劃任務

Service是Android的四大組件之一，這裡就不再過多的去描述，下面主要實現啟動應用時候利用 service後台執行計劃任務，退出應用後，關閉service,只存在整個應用的周期中。

首先使用service需要在manifest中的Application 中注冊

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

 </service>

寫一個WxService類，繼承於Service,然後實現它的一些方法。

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()方法中去調度計劃,下面介紹一個這個Schedule類。

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.
說明：該方法會在指定的延時後執行任務，並且在設定的周期定時執行任務。