如何使后台运行的程序获取按键事件

2022-04-23 07:06:28

一、基本思路：

首先程序运行时注册按键事件，然后将程序转入后台运行，当按键事件发生后在AppUi的HandleKeyEventL中处理。

相关代码如下：

void CClockSSAppUi::SetCaptureKey()
{
    // If there is another handle, we have to cancel it first.
    CancelCaptureKey();
    // This will capture scan code of the keypress.
    iHandleCaptureKey = CCoeEnv::Static()-> RootWin().CaptureKeyUpAndDowns(
      KOkKeyScanCode, EModifierShift, EModifierShift PRIORITYCAPTUREKEY);

    //// WARNING: We need to capture the normal code of keypress otherwise
    // the key event will be sent to another application.
    iHandleCaptureKey2 = CCoeEnv::Static()-> RootWin().CaptureKey(
      KOkKeyCode, EModifierShift, EModifierShift PRIORITYCAPTUREKEY);
}

TKeyResponse CClockSSAppUi::HandleKeyEventL(const TKeyEvent& aKeyEvent,TEventCode aType)
{
if ((KOkKeyScanCode == (TUint) aKeyEvent.iScanCode) && (EEventKeyDown == aType)
          && ((aKeyEvent.iModifiers & EModifierShift) == EModifierShift) )
          {
          CAknGlobalNote* globalNote = CAknGlobalNote::NewLC();
          globalNote->ShowNoteL(EAknGlobalInformationNote, _L(”Captured KEY!”));
          CleanupStack::PopAndDestroy();
          }
}

需要注意的是：如果你的是多view程序，并且调用了AppUi::AddToStackL接收按键事件，那么在这些控件OfferKeyEventL的处理中对于不相关的键事件一定要返回EKeyWasNotConsumed,好让AppUi最后能处理。

二、如何将程序送到后台运行

比如说，当按下back后，在HandleCommandL()中加入如下处理：
case EAknSoftkeyBack:
            {
            TApaTask apaTask(iEikonEnv->WsSession());
            apaTask.SetWgId(CCoeEnv::Static()->RootWin().Identifier());
            apaTask.SendToBackground();
            break;
            }

解释一下：
A task is a running application.
A task is identified by its association with the running application’s window group.
apaTask把自己送到后台，并在后台继续运行。

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