2004. január 3., szombat

Differentiating Between the Two ENTER Keys


How to find difference between the two ENTER keys?


An application may find it useful to differentiate between the user pressing the ENTER key on the standard keyboard and the ENTER key on the numeric keypad. Either action creates a WM_KEYDOWN message and a WM_KEYUP message with wParam set to the virtual key code VK_RETURN. When the application passes these messages to TranslateMessage, the application receives a WM_CHAR message with wParam set to the corresponding ASCII code 13.

To differentiate between the two ENTER keys, test bit 24 of lParam sent with the three messages listed above. Bit 24 is set to 1 if the key is an extended key; otherwise, bit 24 is set to 0 (zero).

Because the keys in the numeric keypad (along with the function keys) are extended keys, pressing ENTER on the numeric keypad results in bit 24 of lParam being set, while pressing the ENTER key on  the standard keyboard results in bit 24 clear.

The following code sample demonstrates differentiating between these two ENTER keys:

procedure TForm1.WMKeyDown(var Message: TWMKeyDown);
  case Message.CharCode of
      begin // ENTER pressed
        if (Message.KeyData and $1000000 <> 0) then // Test bit 24 of lParam
          // ENTER on numeric keypad

          // ENTER on the standard keyboard


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