How to edit/reset Alarm Manager?

I've set up a Preference Screen in which i have a list preference which allows user to select time interval to notify them.

They can choose whether to notify them after every 2,4,8,10 or 12 hours.

Here's my list preference:

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android" >
<ListPreference
            android:title="Notification Timer"
            android:summary="Select when to Notify"
            android:dialogTitle="Show Notification after every:"
            android:positiveButtonText="OK"
            android:negativeButtonText="Cancel"
            android:entries="@array/entries"
            android:entryValues="@array/entries"
            android:key="listPrefs" />
</PreferenceScreen>

Here's my Settings.class file:

public class Settings extends PreferenceActivity implements OnPreferenceChangeListener{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.settings);

        ListPreference listPreference = (ListPreference) findPreference("listPrefs");
        listPreference.setOnPreferenceChangeListener(new Preference.OnPreferenceChangeListener() {

            @Override
            public boolean onPreferenceChange(Preference preference, Object newValue) {

                return false;
            }
        });
        @Override
    public boolean onPreferenceChange(Preference preference, Object newValue) {
        // TODO Auto-generated method stub
        return false;
    }
}

I want to update or reset Alarms every time the user changes the time interval of notifying him/her. for ex- If user selects 4 hours than he/she must be notified after 4 hours or if user chooses 10 hours than he/she must be notified after 10 hours!

Follow these steps:

1. Copy the following methods to your Setting.java file:

   private final int NOTIFICATION_TIMER = 11;
   
   public void setAlarm(Context mContext,int requestCode,long time) {
   
       Intent myIntent = new Intent(mContext, AlarmReceiver.class);
       PendingIntent pendingIntent = PendingIntent.getBroadcast(mContext, requestCode, myIntent,0);
   
       cancelAlarmIfExists(mContext,requestCode,myIntent);
   
       AlarmManager alarmManager = (AlarmManager)mContext.getSystemService(ALARM_SERVICE);
       alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, (System.currentTimeMillis()+time), time, pendingIntent);
   }
   
   public void cancelAlarmIfExists(Context mContext,int requestCode,Intent intent){
       try {
           PendingIntent pendingIntent = PendingIntent.getBroadcast(mContext, requestCode, intent,0);
           AlarmManager am=(AlarmManager)mContext.getSystemService(Context.ALARM_SERVICE);
           am.cancel(pendingIntent);
       } catch (Exception e) {
           e.printStackTrace();
       }
   }
   

2. Call them from the onPreferenceChange() method. Like so:

   listPreference.setOnPreferenceChangeListener(new Preference.OnPreferenceChangeListener() {
       @Override
       public boolean onPreferenceChange(Preference preference, Object newValue) {
   
           long time = 34352355253; // calculate millisecons from change value by user.
           setAlarm(Settings.this,NOTIFICATION_TIMER,time);
           return false;
       }
   });