How can i receive notifications of registery changes in Delphi?

In Delphi, you can use the Windows API function RegNotifyChangeKeyValue to receive notifications of changes to a specified registry key.

Here is an example of how to use this function in Delphi:

1. Declare the function in the implementation section of your unit:
   
   Delphi/Pascal

   function RegNotifyChangeKeyValue(hKey: HKEY; bWatchSubtree: BOOL; dwNotifyFilter: DWORD; hEvent: THandle; fAsynchronous: BOOL): Longint; stdcall; external advapi32;

   1	function RegNotifyChangeKeyValue(hKey: HKEY; bWatchSubtree: BOOL; dwNotifyFilter: DWORD; hEvent: THandle; fAsynchronous: BOOL): Longint; stdcall; external advapi32;

2.  Create a handle to the registry key you want to monitor, using the Windows API function RegOpenKeyEx.
   
   Delphi/Pascal

   var hKey: HKEY; begin RegOpenKeyEx(HKEY_LOCAL_MACHINE, ‘SOFTWARE\MyCompany\MyApplication’, 0, KEY_NOTIFY, hKey);Call the RegNotifyChangeKeyValue function to register for notifications.

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   var   hKey: HKEY; begin   RegOpenKeyEx(HKEY_LOCAL_MACHINE, ‘SOFTWARE\MyCompany\MyApplication’, 0, KEY_NOTIFY, hKey);Call the RegNotifyChangeKeyValue function to register for notifications.

3.  Call the RegNotifyChangeKeyValue function to register for notifications.
   
   Delphi/Pascal

   RegNotifyChangeKeyValue(hKey, True, REG_NOTIFY_CHANGE_LAST_SET, Handle, True);

   1	RegNotifyChangeKeyValue(hKey, True, REG_NOTIFY_CHANGE_LAST_SET, Handle, True);

   
   The first parameter is the handle to the key you want to monitor, the second parameter specifies whether to monitor the key and its subkeys, the third parameter specifies the types of changes to watch for (in this case, changes to the value of the key), the fourth parameter is a handle to an event that will be signaled when a change occurs, and the fifth parameter specifies whether the function should return immediately or wait for a change to occur.
4. Wait for the event to be signaled using the WaitForSingleObject function:
   
   Delphi/Pascal

   while WaitForSingleObject(Handle, INFINITE) = WAIT_OBJECT_0 do begin // Do something when a change occurs end;

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   while WaitForSingleObject(Handle, INFINITE) = WAIT_OBJECT_0 do begin   // Do something when a change occurs end;

5. Close the handle to the registry key when you are done:
   
   Delphi/Pascal

   RegCloseKey(hKey);

   1	RegCloseKey(hKey);

   
   It is important to note that, this is just an example on how to use the RegNotifyChangeKeyValue function in Delphi, it could be improved with error checking and handling.
   6. Make sure to handle errors that may occur when calling the Windows API functions. For example, you can check the return value of RegOpenKeyEx to ensure that the function succeeded in opening the key. You can also use the GetLastError function to retrieve the error code if a function fails.
   7. Depending on the requirements of your application, you may need to handle multiple registry keys or use different filters to monitor different types of changes.
   8. When you are done monitoring the registry key, make sure to unregister the notification by calling the RegNotifyChangeKeyValue function again with the same parameters, but with the hEvent parameter set to NULL.
   9. If you want to monitor the key from another thread, you can use the TThread.Synchronize method to call the RegNotifyChangeKeyValue and other API functions, to avoid thread-safety issues.
   10. Keep in mind that the RegNotifyChangeKeyValue function is available only on Windows NT and later, and it may not work as expected on older versions of Windows.

   Here is an example how the function could look in Delphi:

   Delphi/Pascal

   procedure TForm1.MonitorRegistry; var hKey: HKEY; dwRet: DWORD; Handle: THandle; begin Handle := CreateEvent(nil, False, False, nil); try dwRet := RegOpenKeyEx(HKEY_LOCAL_MACHINE, ‘SOFTWARE\MyCompany\MyApplication’, 0, KEY_NOTIFY, hKey); if dwRet = ERROR_SUCCESS then begin dwRet := RegNotifyChangeKeyValue(hKey, True, REG_NOTIFY_CHANGE_NAME or REG_NOTIFY_CHANGE_LAST_SET or REG_NOTIFY_CHANGE_SECURITY, Handle, True); if dwRet = ERROR_SUCCESS then begin while WaitForSingleObject(Handle, INFINITE) = WAIT_OBJECT_0 do begin // Do something when a change occurs end; end else raise Exception.Create(‘RegNotifyChangeKeyValue failed with error code: ‘ + IntToStr(dwRet)); RegCloseKey(hKey); end else raise Exception.Create(‘RegOpenKeyEx failed with error code: ‘ + IntToStr(dwRet)); finally CloseHandle(Handle); end; end;

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   procedure TForm1.MonitorRegistry; var   hKey: HKEY;   dwRet: DWORD;   Handle: THandle; begin   Handle := CreateEvent(nil, False, False, nil);   try     dwRet := RegOpenKeyEx(HKEY_LOCAL_MACHINE, ‘SOFTWARE\MyCompany\MyApplication’, 0, KEY_NOTIFY, hKey);     if dwRet = ERROR_SUCCESS then     begin       dwRet := RegNotifyChangeKeyValue(hKey, True, REG_NOTIFY_CHANGE_NAME or REG_NOTIFY_CHANGE_LAST_SET or REG_NOTIFY_CHANGE_SECURITY, Handle, True);       if dwRet = ERROR_SUCCESS then       begin         while WaitForSingleObject(Handle, INFINITE) = WAIT_OBJECT_0 do         begin           // Do something when a change occurs         end;       end       else         raise Exception.Create(‘RegNotifyChangeKeyValue failed with error code: ‘ + IntToStr(dwRet));       RegCloseKey(hKey);     end     else       raise Exception.Create(‘RegOpenKeyEx failed with error code: ‘ + IntToStr(dwRet));   finally     CloseHandle(Handle);   end; end;

    

   As you can see in the example, it is important to check the return values of the Windows API functions and handle any errors that may occur.