短视频获客,云南网站建设及优化,福州网站开发cms,wordpress 代码高亮插件参考《Professional Android 4 Development》 Services Service是invisible的#xff0c;因此其优先级不高于visible的Activity#xff0c;之所以说不高于#xff0c;是因为我们可以设置Service为在前台运行。 创建Service Android提供了Service抽象类#xff0c;继承它便可…参考《Professional Android 4 Development》 Services Service是invisible的因此其优先级不高于visible的Activity之所以说不高于是因为我们可以设置Service为在前台运行。 创建Service Android提供了Service抽象类继承它便可以创建一个Service类 import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
public class MyService extends Service {Overridepublic void onCreate() {super.onCreate();// TODO: Actions to perform when service is created.}Overridepublic IBinder onBind(Intent intent) {// TODO: Replace with service binding implementation.return null;}
} 创建Service类之后还需要在Manifest里面注册 service android:enabled”true” android:name”.MyService” android:permission”com.paad.MY_SERVICE_PERMISSION”/ 若要默认只有自己的程序可以使用这个Service需要添加Android:permission属性。其他Application若要使用这个服务需要加入这个permission。 执行Service 当Service由startService()方法调用时即可引起onStartCommand方法的调用因此需要重写Service中的onStartCommand方法并且onStartCommand方法可能会被多次调用。onStartCommand()方法将返回一个int值用于指定当Service被runtime杀掉又重启的时系统该如何响应 Override
public int onStartCommand(Intent intent, int flags, int startId) {startBackgroundTask(intent, startId);return Service.START_STICKY;
} 重启Service onStartCommand()方法可以返回这些参数它们的意义是 START_STICKY如果service进程被kill掉保留service的状态为开始状态但不保留递送的intent对象。随后系统会尝试重新创建service由于服务状态为开始状态所以创建服务后一定会调用onStartCommand(Intent,int,int)方法。如果在此期间没有任何启动命令被传递到service那么参数Intent将为null。 START_NOT_STICKY“非粘性的”。如果在执行完onStartCommand后服务被异常kill掉系统不会自动重启该服务。START_REDELIVER_INTENT使用这个返回值时如果未执行完onStartCommand服务在调用stopSelf之前被kill掉系统会自动重启该服务并将Intent的值传入。 参考http://www.krislq.com/2013/05/android-class-return-value-of-onstartcommand/ 启动和停止服务 调用startService方法可以启动服务 private void explicitStart() {// Explicitly start My ServiceIntent intent new Intent(this, MyService.class);// TODO Add extras if required.startService(intent);
}
private void implicitStart() {// Implicitly start a music ServiceIntent intent new Intent(MyMusicService.PLAY_ALBUM);intent.putExtra(MyMusicService.ALBUM_NAME_EXTRA, “United”);intent.putExtra(MyMusicService.ARTIST_NAME_EXTRA, “Pheonix”);startService(intent);
} 调用stopService方法可以停止服务 // Stop a service explicitly.
stopService(new Intent(this, MyService.class));
// Stop a service implicitly.
Intent intent new Intent(MyMusicService.PLAY_ALBUM);
stopService(intent); 服务自杀 服务内部调用stopSelf方法可以停止该服务。 绑定Service到Activity 首先Service要实现IBind接口 Override
public IBinder onBind(Intent intent) {return binder;
}
public class MyBinder extends Binder {MyMusicService getService() {return MyMusicService.this;}
}
private final IBinder binder new MyBinder(); ServiceConnection类用于表示Service到Activity的绑定每个绑定都需要创建一个ServiceConnection // Reference to the service
private MyMusicService serviceRef;
// Handles the connection between the service and activity
private ServiceConnection mConnection new ServiceConnection() {public void onServiceConnected(ComponentName className, IBinder service) {// Called when the connection is made.serviceRef ((MyMusicService.MyBinder)service).getService();}public void onServiceDisconnected(ComponentName className) {// Received when the service unexpectedly disconnects.serviceRef null;}
}; 最后调用bindService方法传入用于启动Service的IntentServiceConnection和标志位 // Bind to the service
Intent bindIntent new Intent(MyActivity.this, MyMusicService.class);
bindService(bindIntent, mConnection, Context.BIND_AUTO_CREATE); 通常情况下Android应用在自己的内存空间中运行并不共享内存。若要与其他进程通信可以使用广播或在Intent中添加Bundle参数启动其他Service的方法。如果需要更紧密的通信可以使用Android Interface Defi nition LanguageAIDL。AIDL使用OS级别的简单变量定义了接口可以跨应用传递对象。 创建前台服务 使用startForeground方法启动服务可以使服务获得与Visible Activity相同的优先级例如 private void startPlayback(String album, String artist) {int NOTIFICATION_ID 1;// Create an Intent that will open the main Activity if the notification is clicked.Intent intent new Intent(this, MyActivity.class);PendingIntent pi PendingIntent.getActivity(this, 1, intent, 0);// Set the Notification UI parametersNotification notification new Notification(R.drawable.icon, “Starting Playback”, System.currentTimeMillis());notification.setLatestEventInfo(this, album, artist, pi);// Set the Notification as ongoingnotification.flags notification.flags | Notification.FLAG_ONGOING_EVENT;// Move the Service to the ForegroundstartForeground(NOTIFICATION_ID, notification);
} 使用stopForeground方法可以取消Service的前台属性 public void pausePlayback() {// Move to the background and remove the NotificationstopForeground(true);
} 使用后台线程 Service和Activity一样也是在主线程中运行的为了更好地响应用户我们需要使用后台线程的方式执行Service。Android提供了两个抽象类来帮助我们实现AsyncTask和IntentService。 使用AsyncTask AsyncTask不仅能帮助我们将费时操作放到后台执行还可以实现和UI线程的同步。AsyncTask适合执行那些耗时比较短并且和UI线程有交互的任务对于耗时较久的任务例如下载使用Service更为合适。需要注意的是AsyncTask在应用restart之后会被cancel掉。 private class MyAsyncTask extends AsyncTaskString, Integer, String {
Override
protected String doInBackground(String... parameter) {
// Moved to a background thread.
String result “”;
int myProgress 0;
int inputLength parameter[0].length();
// Perform background processing task, update myProgress]
for (int i 1; i inputLength; i) {
myProgress i;
result result parameter[0].charAt(inputLength-i);
try {
Thread.sleep(100);
} catch (InterruptedException e) { }
publishProgress(myProgress);
}
// Return the value to be passed to onPostExecute
return result;
}
Override
protected void onProgressUpdate(Integer... progress) {
// Synchronized to UI thread.
// Update progress bar, Notification, or other UI elements
asyncProgress.setProgress(progress[0]);
}
Override
protected void onPostExecute(String result) {
// Synchronized to UI thread.
// Report results via UI update, Dialog, or notifications
asyncTextView.setText(result);
}
} 使用AsyncTask首先要创建一个AsyncTask的子类类并实现doInBackgroundonProgressUpdateonPostExecute方法。这三个方法的说明 doInBackground: 这个方法用于执行需要在后台线程中长期运行的操作可以通过publishProgress方法传递参数给onProgressUpdate在这个方法执行完毕之后此方法将返回值传递给onProgressUpdate。onProgressUpdate: 接收publishProgress方法传入的参数更新UI。onPostExecute: doInBackground执行结束后将返回值传入此方法。执行AsyncTask String input “redrum ... redrum”;
new MyAsyncTask().execute(input); Intent Service简介 IntentService可以通过传入Intent参数调用传入的Intent将进入一个队列中被异步执行。IntentService封装了消息的异步处理后台线程创建以及与UI线程的同步。继承IntentService类并实现onHandleIntent方法即可创建一个Intent Service import android.app.IntentService;
import android.content.Intent;
public class MyIntentService extends IntentService {public MyIntentService(String name) {super(name);// TODO Complete any required constructor tasks.}Overridepublic void onCreate() {super.onCreate();// TODO: Actions to perform when service is created.}Overrideprotected void onHandleIntent(Intent intent) {// This handler occurs on a background thread. TODO The time consuming task should be implemented here.// Each Intent supplied to this IntentService will be processed consecutively here. When all incoming Intents have been processed the Service will terminate itself.}
} Loader简介 Loader是一个抽象类封装了异步加载数据的最佳实践最典型的就是CursorLoader了。Android中创建Loader类的简单方法是继承AsyncTaskLoader类并实现这两个功能 异步加载数据监测数据源的变化并及时更新手动创建线程及GUI线程同步 尽管AsyncTask和Intent Service提供了简单易用的异步类封装但我们也可以创建自定义的异步线程 // This method is called on the main GUI thread.
private void backgroundExecution() {// This moves the time consuming operation to a child thread.Thread thread new Thread(null, doBackgroundThreadProcessing, “Background”);thread.start();
}
// Runnable that executes the background processing method.
private Runnable doBackgroundThreadProcessing new Runnable() {public void run() {backgroundThreadProcessing();}
};
// Method which does some processing in the background.
private void backgroundThreadProcessing() {
// [ ... Time consuming operations ... ]
} 与GUI线程同步: runOnUiThread方法会在UI线程执行 runOnUiThread(new Runnable() {public void run() {// Update a View or other Activity UI element.}
}); 此外可以使用Handler类更新UI线程 //This method is called on the main GUI thread.
private void backgroundExecution() {// This moves the time consuming operation to a child thread.Thread thread new Thread(null, doBackgroundThreadProcessing, “Background”);thread.start();
}
// Runnable that executes the background processing method.
private Runnable doBackgroundThreadProcessing new Runnable() {public void run() {backgroundThreadProcessing();}
};
// Method which does some processing in the background.
private void backgroundThreadProcessing() {
// [ ... Time consuming operations ... ]
// Use the Handler to post the doUpdateGUI
// runnable on the main UI thread.handler.post(doUpdateGUI);
}
//Initialize a handler on the main thread.
private Handler handler new Handler();
// Runnable that executes the updateGUI method.
private Runnable doUpdateGUI new Runnable() {public void run() {updateGUI();}
};
// This method must be called on the UI thread.
private void updateGUI() {
// [ ... Open a dialog or modify a GUI element ... ]
} Handler类还可以使用postDelayed和postAtTime实现推迟运行和推迟指定时间运行 // Post a method on the UI thread after 1sec.
handler.postDelayed(doUpdateGUI, 1000);
// Post a method on the UI thread after the device has been in use for 5mins.
int upTime 1000*60*5;
handler.postAtTime(doUpdateGUI, SystemClock.uptimeMillis()upTime); 使用ALARMS 与Timer不太Alarms属于系统服务独立于应用程序。即使应用程序为启动也可以使用Alarms启动应用程序并获取其服务这样不仅减少了耦合也减少了系统资源的占用。Android中Alarms常与Broadcast Receiver一起使用。创建Alarm之前首先要创建AlarmManager AlarmManager alarmManager (AlarmManager)getSystemService(Context.ALARM_SERVICE); 创建设置和取消ALARMS 创建Alarm需要这些参数alarm类型触发时间Alarm将要触发的Pending Intent。目前Alarm类型有这些 RTC_WAKEUP在指定时间启动指定Pending Intent可以唤醒sleep中的设备。RTC在指定时间启动指定Pending Intent但不能唤醒sleep中的设备。ELAPSED_REALTIME在某段时间后启动指定的Pending Intent某段时间是从设备启动但还没有唤醒设备算起。ELAPSED_REALTIME_WAKEUP 这个和ELAPSED_REALTIME的区别没搞明白以后遇到了再查吧。下面是一个10秒后启动Pending Intent的Alarm示例 AlarmManager alarmManager (AlarmManager)getSystemService(Context.ALARM_SERVICE);
// Set the alarm to wake the device if sleeping.
int alarmType AlarmManager.ELAPSED_REALTIME_WAKEUP;
// Trigger the device in 10 seconds.
long timeOrLengthofWait 10000;
// Create a Pending Intent that will broadcast and action
String ALARM_ACTION “ALARM_ACTION”;
Intent intentToFire new Intent(ALARM_ACTION);
PendingIntent alarmIntent PendingIntent.getBroadcast(this, 0, intentToFire, 0);
// Set the alarm
alarmManager.set(alarmType, timeOrLengthofWait, alarmIntent); 取消Alarm alarmManager.cancel(alarmIntent); 这里的alarmIntent是指使用Alarm启动的Pending Intent。 创建可重复的Alarm 使用setRepeating或setInexactRepeating方法替代前面的set方法并传递响应的参数进去就可以实现可重复的Alarm。 相比setRepeatingsetInexactRepeating更省电但不能指定某个具体的时间间隔。 setInexactRepeating可以接收的时间间隔参数 INTERVAL_FIFTEEN_MINUTESINTERVAL_HALF_HOURINTERVAL_HOURINTERVAL_HALF_DAYINTERVAL_DAY 下面这个例子指定半小时后启动Alarm然后每隔半小时启动一次: // Get a reference to the Alarm Manager
AlarmManager alarmManager (AlarmManager)getSystemService(Context.ALARM_SERVICE);
// Set the alarm to wake the device if sleeping.
int alarmType AlarmManager.ELAPSED_REALTIME_WAKEUP;
// Schedule the alarm to repeat every half hour.
long timeOrLengthofWait AlarmManager.INTERVAL_HALF_HOUR;
// Create a Pending Intent that will broadcast and action
String ALARM_ACTION “ALARM_ACTION”;
Intent intentToFire new Intent(ALARM_ACTION);
PendingIntent alarmIntent PendingIntent.getBroadcast(this, 0, intentToFire, 0);
// Wake up the device to fire an alarm in half an hour, and every half-hour after that.
alarmManager.setInexactRepeating(alarmType, timeOrLengthofWait, timeOrLengthofWait, alarmIntent); 转载于:https://www.cnblogs.com/jubincn/p/3521452.html
