Bring application to foreground with a keypress

本文介绍了一种方法,使应用程序能够在后台捕获按键事件,并通过按下特定按键(如'#'键)将应用程序从后台切换到前台。这种方法涉及设置应用程序为系统级应用、永久捕获指定按键、调整应用优先级等步骤。

 

Bring application to foreground with a keypress

From Forum Nokia Wiki

Inorder to capture the keys while you application under background you've to override CCoeAppUi::HandleWsEventL to your AppUi. With the use of RWindowGroup::CaptureKeyUpAndDowns() you can capture the keys from an application. Below is some sample code which will show you basically how to do it, you may found some additional bit of code which you may use.

 

The mmp file

CAPABILITY    

SwEvent

 

The header file

/**
  * To store the handle to the captured key.
  */

TInt iHashKeyHandle;

The cpp file

// -----------------------------------------------------------------------------


// CMyAppUi::ConstructL()
// Symbian 2nd phase constructor can leave.
// -----------------------------------------------------------------------------
//
void CMyAppUi:: ConstructL ()
    {
    BaseConstructL() ;
 
    // ...
 
    // set application as system application so that it will
    // not be closed by system events
     CEikonEnv:: Static () - > SetSystem( ETrue ) ;
 
    // capture hash '#' key permanently
    iHashKeyHandle = CEikonEnv:: Static () - > RootWin() .CaptureKeyUpAndDowns ( EStdKeyHash, 0, 0) ;
 
    // set application priority to foreground priority even if it goes to background
    CEikonEnv:: Static () - > WsSession() .ComputeMode ( RWsSession:: EPriorityControlDisabled ) ;
 
    // Make the application a high priority application
    CEikonEnv:: Static () - > RootWin() .EnableReceiptOfFocus ( ETrue ) ;
    CEikonEnv:: Static () - > RootWin() .SetOrdinalPosition ( 0, ECoeWinPriorityAlwaysAtFront) ;
    }
 
// -----------------------------------------------------------------------------
// CMyAppUi::~CMyAppUi()
// Destructor.
// -----------------------------------------------------------------------------
//
CMyAppUi:: ~CMyAppUi()
    {
    // Release the hanlde to the captured key.
    CEikonEnv:: Static () - > RootWin() .CancelCaptureKeyUpAndDowns ( iHashKeyHandle) ;
 
    // ...
    }
 
// -----------------------------------------------------------------------------
// CMyAppUi::HandleForegroundEventL(TBool aForeground)
// Handles changes in keyboard focus when the application is brought to the
// foreground, or put into the background.
// -----------------------------------------------------------------------------
//
void CMyAppUi:: HandleForegroundEventL ( TBool aForeground)
    {
    // Make the application a high priority application
    if ( aForeground)
        {
        CEikonEnv:: Static () - > RootWin() .SetOrdinalPosition ( 0, ECoeWinPriorityAlwaysAtFront) ;
        }
    }
 
// -----------------------------------------------------------------------------
// CMyAppUi::HandleWsEventL (const TWsEvent &aEvent, CCoeControl *aDestination)
// Handles events sent to the application by the window server.
// -----------------------------------------------------------------------------
//
void CMyAppUi:: HandleWsEventL ( const TWsEvent & aEvent, CCoeControl * aDestination)
    {
    if ( aEvent.Type () == EEventKey ||
        aEvent.Type () == EEventKeyUp ||
        aEvent.Type () == EEventKeyDown ||
        aEvent.Type () == EEventKeyRepeat)
        {
        // This is for switching back to Application when Hash key is pressed
        if ( EStdKeyHash == aEvent.Key () - > iScanCode && EEventKey == aEvent.Type ())
            {
            TApaTask task( iEikonEnv- > WsSession()) ;
            task.SetWgId ( CEikonEnv:: Static () - > RootWin() .Identifier ()) ;
            task.BringToForeground () ;
 
            return ;
            }
        }
 
        CAknAppUi:: HandleWsEventL ( aEvent, aDestination) ;
    }

 

 

在 Android 开发中,带有前台服务(foreground service)的通知渠道(Notification Channel)不能直接删除,因为系统会阻止这种操作以保护用户体验和系统稳定性。如果尝试强行删除,通常会遇到权限不足或操作被禁止的错误。 要删除一个带有前台服务的通知渠道,必须先停止与该渠道关联的前台服务。可以通过调用 `stopForeground()` 方法来将服务从“前台”状态移除,然后再调用 `deleteNotificationChannel()` 删除通知渠道 [^1]。以下是一个示例代码: ```java public class MyService extends Service { private static final String CHANNEL_ID = "my_channel"; @Override public void onCreate() { super.onCreate(); // 创建通知渠道(仅首次需要) if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) { NotificationChannel channel = new NotificationChannel( CHANNEL_ID, "My Channel", NotificationManager.IMPORTANCE_DEFAULT ); NotificationManager manager = getSystemService(NotificationManager.class); manager.createNotificationChannel(channel); // 将服务置于前台 Notification notification = new Notification.Builder(this, CHANNEL_ID) .setContentTitle("Running in foreground") .build(); startForeground(1, notification); } } public void stopAndDeleteChannel() { // 停止前台服务 stopForeground(true); // 参数 true 表示同时移除通知 // 删除通知渠道 NotificationManager manager = getSystemService(NotificationManager.class); manager.deleteNotificationChannel(CHANNEL_ID); // 这里将删除通知渠道 [^1] } @Override public void onDestroy() { stopAndDeleteChannel(); // 在服务销毁时执行清理 super.onDestroy(); } @Override public IBinder onBind(Intent intent) { return null; } } ``` 需要注意的是,某些设备厂商(如三星、小米等)可能对通知渠道的管理进行了定制化处理,因此在部分设备上即使调用了 `deleteNotificationChannel()` 方法,也可能无法立即生效或者行为不一致。此外,用户也可以通过系统设置手动管理通知渠道。
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