使用Alarm来更新地震

 

在地震例子中,这一次的修改你将使用Alarm来替代Timer,定期执行网络更新。

 

1. 创建一个新的EarthquakeAlarmReceiver类,扩展BroadcastReceiver

 

package com.paad.earthquake;

import android.content.BroadcastReceiver;

import android.content.Context;

import android.content.Intent;

public class EarthquakeAlarmReceiver extends BroadcastReceiver {

}

 

2. 重写onReceive方法来显式启动EarthquakeService

 

@Override

public void onReceive(Context context, Intent intent) {

Intent startIntent = new Intent(context, EarthquakeService.class);

context.startService(startIntent);

}

 

3. 创建一个新的共通的静态字符串来定义用于触发Broadcast Receiver的动作。

 

public static final String ACTION_REFRESH_EARTHQUAKE_ALARM =

“com.paad.earthquake.ACTION_REFRESH_EARTHQUAKE_ALARM”;

 

4. 在manifest中添加新的EarthquakeAlarmReceiver,包含一个intent-filter标签来监听第3步中定义的动作。

 

<receiver android:name=”.EarthquakeAlarmReceiver”>

<intent-filter>

<action

android:name=”com.paad.earthquake.ACTION_REFRESH_EARTHQUAKE_ALARM”

/>

</intent-filter>

</receiver>

 

5. 在EarthquakeService中,更新onCreate方法来获得AlarmManager的一个引用,并创建一个新的PendingIntent,当Alarm到达时发送Intent。你还可以移除timerTask的初始化代码。

 

AlarmManager alarms;

PendingIntent alarmIntent;

@Override

public void onCreate() {

int icon = R.drawable.icon;

String tickerText = “New Earthquake Detected”;

long when = System.currentTimeMillis();

newEarthquakeNotification = new Notification(icon, tickerText, when);

alarms = (AlarmManager)getSystemService(Context.ALARM_SERVICE);

String ALARM_ACTION;

ALARM_ACTION = EarthquakeAlarmReceiver.ACTION_REFRESH_EARTHQUAKE_ALARM;

Intent intentToFire = new Intent(ALARM_ACTION);

alarmIntent = PendingIntent.getBroadcast(this, 0, intentToFire, 0);

}

 

6. 修改onStart方法设置一个Alarm,而不再使用Timer来定期执行下一次更新操作(如果自动更新是enable的)。设置一个新的具有相同动作的Intent来自动取消前一个Alarm

 

@Override

public void onStart(Intent intent, int startId)

{

SharedPreferences prefs = getSharedPreferences(Preferences.USER_PREFERENCE, Activity.MODE_PRIVATE);

int minMagIndex = prefs.getInt(Preferences.PREF_MIN_MAG, 0);

if (minMagIndex < 0)

minMagIndex = 0;

int freqIndex = prefs.getInt(Preferences.PREF_UPDATE_FREQ, 0);

if (freqIndex < 0)

freqIndex = 0;

boolean autoUpdate = prefs.getBoolean(Preferences.PREF_AUTO_UPDATE, false);

Resources r = getResources();

int[] minMagValues = r.getIntArray(R.array.magnitude);

int[] freqValues = r.getIntArray(R.array.update_freq_values);

minimumMagnitude = minMagValues[minMagIndex];

int updateFreq = freqValues[freqIndex];

if (autoUpdate)

{

int alarmType = AlarmManager.ELAPSED_REALTIME_WAKEUP;

long timeToRefresh = SystemClock.elapsedRealtime() + updateFreq*60*1000;

alarms.set(alarmType, timeToRefresh, alarmIntent);

}

else

alarms.cancel(alarmIntent);

refreshEarthquakes();

};

 

7. 你可以移除updateTimer实例变量和TimerTask实例。

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