Categories: Symbian C++ | Games | Code Examples

This page was last modified 22:19, 2 August 2007.

From Forum Nokia Wiki

This article presents a simple class to handle keyboard input in a game-like way.

Class declaration

// INCLUDES
#include <e32keys.h>
#include <e32std.h>
 
// CLASSES
 
/**
 * A simple keyboard wrapper.
 */
class TKeyboardWrapper
{
  public:
	
    // key codes not found in header files
    enum TKeys {
		EKey0 = 48,
		EKey1,
		EKey2,
		EKey3,
		EKey4,
		EKey5,
		EKey6,
		EKey7,
		EKey8,
		EKey9,
		EKeyShift = 127,
		EKeyStar  = 133			
		};
 
  public:
	
  /**
   * Default constructor.
   */
  TKeyboardWrapper ()
  { Clear (); }
		
		
  /**
   * Clears key state.
   */
  void Clear ()
  { Mem::FillZ (iKeys, 256); }
		 
		 
  /**
   * Asks if some key is down.
   */
  TBool IsKeyDown (TInt aKey) const
  { ASSERT (aKey >= 0 && aKey < 256); return iKeys [aKey]; }
		 
		
  /**
   * Sets a key as down.
   */
  void SetKey (TInt aKey)
  { ASSERT (aKey >= 0 && aKey < 256); iKeys [aKey] = ETrue; }
		 
		
  /**
   * Sets a key as up.
   */
  void ClearKey (TInt aKey)
  { ASSERT (aKey >= 0 && aKey < 256); iKeys [aKey] = EFalse; }
		 
		
  /** 
   * Check if any key is down.
   */
  TBool AnyKeyDown () const
  {
    for (TInt16 i = 0; i < 256; ++i)
     {
       if (iKeys [i])
	return true;
     }
			
    return false;
  }
 
  private:
    TBool iKeys [256];
};

Usage

It is necessary to collect the keyboard data in some of the methods that receive keyboard input. For example, using the HandleKeyEventL() of the Application UI class:

TKeyResponse CMyAppUi::HandleKeyEventL (const TKeyEvent& aKeyEvent, TEventCode aType)
{	
	if (aType == EEventKeyDown)
	 iKeyboard.SetKey (aKeyEvent.iScanCode);
	else
	if (aType == EEventKeyUp)
	 iKeyboard.ClearKey (aKeyEvent.iScanCode);
 
	return EKeyWasConsumed;
}

In the example, iKeyboard is a TKeyboardWrapper instance. Later, to get the key state it is necessary to use the constants defined in the TStdScanCode enum (e32keys.h). Example:

void CMyAppUi::ProcessInput ()
{
  if (iKeyboard [EStdKeyLeftArrow] )
    // left arrow is down
 
  if (iKeyboard [TKeyboardWrapper::EKey0] )
    // 0 key is down
 
}

It is important not to use the constants defined in the TKeyCode enum, because their use leads to incorrect behavior and possibly to an invalid array access.