How to prevent user from powering off the PDA

How to prevent user from powering off the PDA

• JKountouroglou

  I would really like to know this too. If anyone has any ideas, could you please help
  

• TexasDeveloper

  I've found some stuff on power.  Namely the POWER_ACTION_POLICY in which it looks like you can change your the way in which a power down will occur.  I guess alternatively, you could somehow change the power down status, so that the power down/suspend event is ignored and then you yourself use the VK_OFF keyboard event to do whatever you want.

  
  

• Anil Dhiman

  If you are still interested, I've done it in my application.

  Basically you have to set up a keyboard hook. I read things saying these weren't available in Wndows CE 5.0, but I tried my app on that platform, and it worked.

  The whole code is as follows:

  #include <tpcshell.h>

  // Sets up the keyboard hook for the device
  //WINCEKBHOOK_API BOOL ActivateKBHook(HINSTANCE hInstance, HOOKPROC LLKeyboardHookCallbackFunction)
  BOOL ActivateKBHook(HINSTANCE hInstance, HOOKPROC LLKeyboardHookCallbackFunction)
  {
  //we need to manually load these standard Win32 API calls
  //MSDN states that these aren't supported in WinCE
  SetWindowsHookEx = NULL;
  CallNextHookEx = NULL;
  UnhookWindowsHookEx = NULL;
  
  //now load the coredll.dll
  g_hHookApiDLL = LoadLibrary(_T("coredll.dll"));
  if(g_hHookApiDLL == NULL)
  {
  //something is awfully wrong
  //the dll has to be present
  MessageBox(NULL, L"Can't Load coredll", L"Error", MB_OK);
  return false;
  }
  else
  {
  //load the SetWindowsHookEx API call
  //the SetWindowsHookEx function installs an application-defined hook procedure into a hook chain.
  //You would install a hook procedure to monitor the system for certain types of events.
  //here we use use the hook to monitor kyeboard events
  SetWindowsHookEx = (_SetWindowsHookExW)GetProcAddress(g_hHookApiDLL, _T("SetWindowsHookExW"));
  if(SetWindowsHookEx == NULL)
  {
  //this means that MS has really stopped supporting this API in WinCE
  MessageBox(NULL, L"Can't use SetWindowsHookEx!", L"Error", MB_OK);
  return false;
  }
  else
  {
  //install the KB hook
  //the handle needs to be saved for default processing of the events and to uninstall the hook, once we are done with it
  g_hInstalledLLKBDhook = SetWindowsHookEx(WH_KEYBOARD_LL, LLKeyboardHookCallbackFunction, NULL, 0);
  if(g_hInstalledLLKBDhook == NULL)
  {
  MessageBox(NULL, L"Can't Set Hook", L"Error", MB_OK);
  return false;
  }
  }
  
  //load CallNextHookEx() API call
  //the CallNextHookEx function passes the hook information to the next hook procedure in the current hook chain.
  //we use this call for default processing of events.
  CallNextHookEx = (_CallNextHookEx)GetProcAddress(g_hHookApiDLL, _T("CallNextHookEx"));
  if(CallNextHookEx == NULL)
  {
  MessageBox(NULL, L"Can't Call Hook", L"Error", MB_OK);
  return false;
  }
  
  
  //load UnhookWindowsHookEx() API
  //the UnhookWindowsHookEx function removes a hook procedure installed in a hook chain by the SetWindowsHookEx function.
  //we use this call to unistall the hook.
  UnhookWindowsHookEx = (_UnhookWindowsHookEx)GetProcAddress(g_hHookApiDLL, _T("UnhookWindowsHookEx"));
  if(UnhookWindowsHookEx == NULL)
  {
  MessageBox(NULL, L"Can't Unhook Hook", L"Error", MB_OK);
  return false;
  }
  }
  
  //all the APIs are loaded and the application is hooked
  return true;
  }
  
  // Unhooks teh keyboard so it can function without this program
  //WINCEKBHOOK_API BOOL DeactivateKBHook()
  BOOL DeactivateKBHook()
  {
  //unload the hook
  if(g_hInstalledLLKBDhook != NULL)
  {
  UnhookWindowsHookEx(g_hInstalledLLKBDhook);
  g_hInstalledLLKBDhook = NULL;
  }
  //unload the coredll.dll
  if(g_hHookApiDLL != NULL)
  {
  FreeLibrary(g_hHookApiDLL);
  g_hHookApiDLL = NULL;
  }
  //we have terminated gracefully
  return true;
  }
  

  /****************************************************************
  WH_KEYBOARD_LL hook procedure
  ****************************************************************/
  LRESULT CALLBACK LowLevelKeyboardProc(int nCode, WPARAM wParam, LPARAM lParam)
  {
  
  PKBDLLHOOKSTRUCT kb = (PKBDLLHOOKSTRUCT)lParam;
  SHSendBackToFocusWindow(nCode,wParam,lParam);
  LRESULT lResult = 0;
  
  // Do not process message
  if (nCode < 0)
  return CallNextHookEx(g_hInstalledLLKBDhook, nCode, wParam, lParam);
  
  if ((nCode == HC_ACTION) )
  {
  switch(kb->vkCode)
  {
  case VK_OFF:
  // Don't send the off message to the system
  lResult = 1;
  break;
  }
  }
  
  // Pass it along so it can be processed
  if (lResult == 0)
  lResult = CallNextHookEx(g_hInstalledLLKBDhook, nCode, wParam, lParam);
  
  // Return true if hook was handled, false to pass it on
  return lResult;
  }
  

  That all goes in your C file. For your header file:

  #ifndef _WINCE_KB_HOOK_H
  #define _WINCE_KB_HOOK_H
  //used for passing to SetWindowsHookEx funtion to set a Low level (LL) keyboard hook
  #define WH_KEYBOARD_LL 20
  // Define the function types used by hooks
  typedef LRESULT (CALLBACK* HOOKPROC)(int nCode, WPARAM wParam, LPARAM lParam);
  typedef HHOOK (WINAPI *_SetWindowsHookExW)(int, HOOKPROC, HINSTANCE, DWORD);
  typedef LRESULT (WINAPI *_CallNextHookEx)(HHOOK, int, WPARAM, LPARAM);
  typedef LRESULT (WINAPI *_UnhookWindowsHookEx)(HHOOK);
  // For the low level keyboard hook, your keyboards procedures is passed a pointer to KBDLLHOOKSTRUCT instance
  typedef struct {
  DWORD vkCode;
  DWORD scanCode;
  DWORD flags;
  DWORD time;
  ULONG_PTR dwExtraInfo;
  } KBDLLHOOKSTRUCT, *PKBDLLHOOKSTRUCT;
  // Win32 Hook APIs
  static _SetWindowsHookExW SetWindowsHookEx;
  static _UnhookWindowsHookEx UnhookWindowsHookEx;
  static _CallNextHookEx CallNextHookEx;
  //WINCEKBHOOK_API BOOL ActivateKBHook(HINSTANCE hInstance, HOOKPROC LLKeyboardHookCallbackFunction);
  BOOL ActivateKBHook(HINSTANCE hInstance, HOOKPROC LLKeyboardHookCallbackFunction);
  //WINCEKBHOOK_API BOOL DeactivateKBHook();
  BOOL DeactivateKBHook();
  #endif
  

  And that's it. It should all work for you now.

  
  
• How to prevent user from powering off the PDA