4、全局定时器：AlermManager
全局定时器是与应用程序独立的系统时间服务，并不依赖应用程序而存在。
该对象通过
AlarmManage alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);获得。
通过PendingIntent指定一个Activity，再通过setRepeating方法设置定时器
intent = new Intent(this, MyActivity.class); pendingActivityIntent = PendingIntent.getActivity(this, 0, intent, 0); alarmManager.setRepeating(AlarmManager.RTC, 0, 5000, pendingActivityIntent);
通过全局定时器，我们来演示一个每5秒更换手机壁纸的程序：
更换壁纸的Service类：
public class ChangeWallpaperService extends Service
{
private static int index = 0;
private int[] resIds = new int[]
{ R.raw.wp1, R.raw.wp2, R.raw.wp3, R.raw.wp4, R.raw.wp5
};
@Override
public void onStart(Intent intent, int startId)
{
if(index == 5)
index = 0;
InputStream inputStream = getResources().openRawResource(resIds[index++]);
try
{
setWallpaper(inputStream);
}
catch (Exception e)
{
}
super.onStart(intent, startId);
}
@Override
public void onCreate()
{
super.onCreate();
}
@Override
public IBinder onBind(Intent intent)
{
// TODO Auto-generated method stub
return null;
}
在mainfirst中配置
<uses-permission android:name="android.permission.SET_WALLPAPER" />
全局定时器：
public class Main extends Activity implements OnClickListener
{
private Button btnStart;
private Button btnStop;
@Override
public void onClick(View view)
{
AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
PendingIntent pendingIntent = PendingIntent.getService(this, 0,
new Intent(this, ChangeWallpaperService.class), 0);
switch (view.getId())
{
case R.id.btnStart:
alarmManager.setRepeating(AlarmManager.RTC, 0, 5000,
pendingIntent);
btnStart.setEnabled(false);
btnStop.setEnabled(true);
break;
case R.id.btnStop:
alarmManager.cancel(pendingIntent);
btnStart.setEnabled(true);
btnStop.setEnabled(false);
break;
}
}
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
btnStart = (Button) findViewById(R.id.btnStart);
btnStop = (Button) findViewById(R.id.btnStop);
btnStop.setEnabled(false);
btnStart.setOnClickListener(this);
btnStop.setOnClickListener(this);
}
}
在创建PendingIntent对象时与service绑定，那么AlarmManager在执行时就会执行service的onStart方法（不是onCreate方法，因为他只会执行一次），获得Service的PendingIntent对象是使用getService方法，同理getActivity，getBroadcast。
下面演示另一个全局定时器的例子，本例是实现多次定时提醒功能。
定时提醒的原理：在添加时间节点后，需要将所添加的时间节点保存在文件或数据库中。本例使用前面介绍过的SharedPreferances来保存。然后使用AlarmManager每隔一分钟扫描一次，在扫描过程中获得当前时间的value，如果成功则说明当前时间为时间点，否则继续扫描。
本例使用BroadcastReceiver来处理定时提醒任务：
public class AlarmReceiver extends BroadcastReceiver
{
@Override
public void onReceive(Context context, Intent intent)
{
SharedPreferences sharedPreferences = context.getSharedPreferences(
"alarm_record", Activity.MODE_PRIVATE);
String hour = String.valueOf(Calendar.getInstance().get(
Calendar.HOUR_OF_DAY));
String minute = String.valueOf(Calendar.getInstance().get(
Calendar.MINUTE));
String time = sharedPreferences.getString(hour + ":" + minute, null);
if (time != null)
{
MediaPlayer mediaPlayer = MediaPlayer.create(context, R.raw.ring);
mediaPlayer.start();
}
}
}
配置文件：
<receiver android:name=".AlarmReceiver" android:enabled="true" />主程序中每添加一个时间点就会在XML文件中保存所添加的时间点：
public class Main extends Activity implements OnClickListener
{
private TextView tvAlarmRecord;
private SharedPreferences sharedPreferences;
@Override
public void onClick(View v)
{
View view = getLayoutInflater().inflate(R.layout.alarm, null);
final TimePicker timePicker = (TimePicker) view
.findViewById(R.id.timepicker);
timePicker.setIs24HourView(true);
new AlertDialog.Builder(this).setTitle("设置提醒时间").setView(view)
.setPositiveButton("确定", new DialogInterface.OnClickListener()
{
@Override
public void onClick(DialogInterface dialog, int which)
{
String timeStr = String.valueOf(timePicker
.getCurrentHour())
+ ":"
+ String.valueOf(timePicker.getCurrentMinute());
tvAlarmRecord.setText(tvAlarmRecord.getText()
.toString()
+ "\n" + timeStr);
sharedPreferences.edit().putString(timeStr, timeStr)
.commit();
}
}).setNegativeButton("取消", null).show();
}
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button btnAddAlarm = (Button) findViewById(R.id.btnAddAlarm);
tvAlarmRecord = (TextView) findViewById(R.id.tvAlarmRecord);
btnAddAlarm.setOnClickListener(this);
sharedPreferences = getSharedPreferences("alarm_record",
Activity.MODE_PRIVATE);
AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
Intent intent = new Intent(this, AlarmReceiver.class);
PendingIntent pendingIntent = PendingIntent.getBroadcast(this, 0,
intent, 0);
alarmManager
.setRepeating(AlarmManager.RTC, 0, 60 * 1000, pendingIntent);
}
}
