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Library File Error - "Class Not Registered"
  • Hello everyone.
    • Sorry for the outline form. 
    • I was unaware the posting process stripped newline characters from the post.
  • The Background -
    • We have a Soft Phone application that is written in Delphi (O.O.D. Pascal) for Windows.
    • The ability to answer an incoming call by activating the answer button on the Plantronics Wireless Headset was recently requested.
    • The MSI files were downloaded and executed, and the Plantronics SDK was downloaded as well and converted / altered into a Delphi Library File.
    • I then started to follow the "First Steps" section of the Plantronics website. 
    • I knew that the "First Steps" code would have to be tweaked to fit the Delphi system.
  • The Problem -
    • In adjusting the code to work within Delphi, a few translations problems were encountered and resolved.
    • One error is proving to be stubborn - when an instance of one specific class is created, the error "Class not registered" is thrown.
      • "First Steps" code for reference -
        • //  Connect to the Plantronics COM API:
          • myAppName = "SDK .NET COM sample";
          • sessionManager = new COMSessionManager();
          • sessionManager.Register(myAppName, out session);
        • //  Hook to SessionManager events:
          • sessionManagerEvents = sessionManager as ICOMSessionManagerEvents_Event;
          • if (sessionManagerEvents != null)
          • {
            • sessionManagerEvents.onCallStateChanged += SessionManagerEvents_onCallStateChanged;
            • sessionManagerEvents.onDeviceStateChanged += SessionManagerEvents_onDeviceStateChanged;
          • }
      • Delphi Code -
        • //  Connect to the Plantronics COM API:
          • plugin_name := "Plugin Name";
          • the_session := CoCOMSession.Create;
          • session_manager := CoCOMSessionManager.Create;
          • session_manager.Register(plugin_name, the_session);
        • //  Hook to Session Manager events:
          • state_device_event_args := CoCOMStateDeviceEventArgs.Create;
          • call_event_args := CoCOMCallEventArgs.Create;
  • The problem is the bold line of the Delphi code. 
    • A CoCOMSession (the_session), a CoCOMSessionManager (session_manager), and a CoCOMStateDeviceEventArgs (state_device_event_args) objects are created without issue. 
    • However, attempting to create a CoCOMCallEventArgs object (call_event_args) throws a "Class Not Registered" error, even though it is declared and implemented in the library file along with the other three.
  • Excerpts from the Library file:
    • Class Declaration:
      • IID_ICOMCallEventArgs: TGUID = '{0280956C-C644-4CD8-B124-C8A99E5D505E}';
      • CLASS_COMCallEventArgs: TGUID = '{705129C3-2265-4F10-9768-0FF8A20234C0}';
    • Class creation function:   
      • class function CoCOMCallEventArgs.Create: ICOMCallEventArgs;
      • begin
        • Result := CreateComObject(CLASS_COMCallEventArgs) as ICOMCallEventArgs;
      • end;
Every tutorial / forum answer about resolving the "Class Not Registered" error that I have found has not resolved the issue. Does anyone have any advice / insight as to what I have been doing wrong? Thank you.  

Hi Duncan,

Declaring and implementing the class in the library file is not enough. It also must be registered in Computer\HKEY_CLASSES_ROOT in the registry.

For example the Plantronics SDK has the following class registered (this is the COMSessionManagerClass):


When Plantronics Hub or Plantronics SDK is installed, this class GUID can be found in the registry under Computer\HKEY_CLASSES_ROOT.

Can you confirm if the class (GUID) you are trying to use exists in the registry?


All of the classes are in the registry, except for the one in question. Upon adding it to the registry, the system was still throwing the "Class not registered" error. The issue has been (potentially) resolved by the following -
  • I had mistakenly thought from the tutorial / first steps section that a "COMCallEventArgs" object needed to be created before it could be used. 
  • Upon further review, the COMCallEventArgs object gets created when necessary at a later point.
More testing needs to be done, but I believe this issue is resolved.

Good to hear! Let me know if further questions!

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