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Key down events in a CView derived class

Posted on 2009-05-12
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Last Modified: 2013-11-20
HIya

I have an SDI application. How can I capture the event when Ctrl + A, Tab + A or a key from the numeric keypad are pressed e.g. PgUp.

John
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Question by:IssacJones
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7 Comments
 
LVL 31

Expert Comment

by:Zoppo
ID: 24362593
Hi IssacJones,

well, for simple keystrokes like 'Ctrl-A' easiest is to use the view's default command message handling by adding a new command for this keystroke in the application's accelerator table.

'Tab-A' is not a single keystroke, are you sure you need it and it's not a typo?

To distinguish between keystrokes on numeric keypad you directly have to handle WM_KEYDOWN message - unfortunateley this only can be done within a overridden PreTranslateMessage function since the view doesn't pass unhandled keystroke-messages to a WM_KEYDOWN message handler.

To do so override the PreTranslateMessage function of the view and implement it somehow like this:

> BOOL CTestViewSDIView::PreTranslateMessage(MSG* pMsg)
> {
>       if ( pMsg->message == WM_KEYDOWN )
>       {
>             if ( pMsg->wParam == VK_PRIOR )
>             {
>                  bool bNumPad = ( pMsg->lParam & ( 1 << 24 ) ) == 0; // see MSDN about WM_KEYDOWN for description of extended-key flag
>
>                  TRACE( "PageUp pressed (extended: %s)\n", false == bNumPad ? "false" : "true" );
>
>                  // don't pass it to the view's default message handler as long as you handle it yourself
>                  return TRUE;
>            }
>      }
>
>      return CView::PreTranslateMessage(pMsg);
> }

Hope this helps,

ZOPPO
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LVL 19

Assisted Solution

by:alb66
alb66 earned 25 total points
ID: 24363673
>>>> 'Tab-A' is not a single keystroke
Zoopo is right. But if you need that for your reason, may be you can handle WM_KEYDOWN for key A, and test the Tab state via GetAsyncKeyState().
0
 

Author Comment

by:IssacJones
ID: 24363789
Hi Zoppo

Many thanks for your help. I didn't explain the "single keystroke" very well. What I was planning to trap was when a user presses Tab and A simultaneously e.g. in a similar manner in Visual Studio you can press Ctrl and Tab at the same time to cycle through files.

Indeed, what I want to do with trapping Tab and A at the same time is to cycle through some views. I thought I'd worked out how to do this but now I suspect I need help with this as well. There are two views that I want to cycle through. Both views are in two seperate functions which I'm going to call  in OnDraw.

Any ideas on how to do it?

John
0
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LVL 31

Expert Comment

by:Zoppo
ID: 24363858
Hi again,

well, IMo it's quite unusual to combine two keys for a command - CTRL, SHIFT and ALT are treated as some kind of state-modifiers for a pressed key, TAB and A are treated as single keystrokes.

Anyway, it can be done either the way alb66 suggested - see attached code for this ...

ZOPPO


BOOL CTestViewSDIView::PreTranslateMessage(MSG* pMsg)

{

	if ( pMsg->message == WM_KEYDOWN )

	{

		if ( pMsg->wParam == VK_PRIOR )

		{

			bool bNumPad = ( pMsg->lParam & ( 1 << 24 ) ) == 0; // see MSDN about WM_KEYDOWN for description of extended-key flag
 

			TRACE( "PageUp pressed (extended: %s)\n", false == bNumPad ? "false" : "true" );

		}

		else if ( pMsg->wParam == 'A' )

		{

			if ( GetKeyState( VK_TAB ) < 0 )

			{

				TRACE( "A+TAB pressed ...\n" );

			}

		}
 

		// don't pass it to the view's default message handler

		return TRUE;

	}
 

	return CView::PreTranslateMessage(pMsg);

}

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0
 

Author Comment

by:IssacJones
ID: 24364019
Hi Zoppo

Ah, okay, could I bother you with one final thing, what would be the best way to deal with Ctrl and Tab i.e. the same as the example I gave with Visual Studio?

John
0
 
LVL 31

Accepted Solution

by:
Zoppo earned 100 total points
ID: 24364142
No problem - For Ctrl-TAB accelerators even don't work (since I guess it is somehow handled especially by MFC), but you can do it the same way:

> ...
> else if ( pMsg->wParam == VK_TAB )
> {
>  if ( GetKeyState( VK_CONTROL ) < 0 )
>  {
>   TRACE( "Ctrl+TAB pressed ...\n" );
>  }
> }
> ...

ZOPPO
0
 

Author Comment

by:IssacJones
ID: 24364166
Excellent! I'll allocate points to both of you because I learnt something new from you both.
0

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