Question

I have the following two classes:

TcmTPDataPanel = class(TcmTPBasePanel)     Database: TnxDatabase;     Session: TnxSession;   private     FDataConnector: TcmTPDataConnector;     MyNxDataBase: TnxDatabase;     MyNxSession: TnxSession;     MyRefNxDataBase: TnxDatabase;   protected     procedure Disconnect; virtual; abstract;     procedure Refresh; virtual;     procedure Requery; virtual; abstract;   public     procedure Connect;   published     property DataConnector: TcmTPDataConnector read FDataConnector write         FDataConnector;   end;   TcmTPDataConnector = class(TComponent)   private     FDatabase: TnxDatabase;     FObservers: TList;     FTableForCategories: TnxTable;     FTableForItemCategoryLinks: TnxTable;     FTableForItems: TnxTable;     procedure SetTableForItemCategoryLinks(const Value: TnxTable);   protected     procedure IterateObservers;   public     constructor Create;     destructor Destroy; override;     procedure Register(Instance: TcmTPDataPanel);     procedure Unregister(Instance: TcmTPDataPanel);   published     property Database: TnxDatabase read FDatabase write FDatabase;     property TableForCategories: TnxTable read FTableForCategories write         FTableForCategories;     property TableForItemCategoryLinks: TnxTable read         FTableForItemCategoryLinks write SetTableForItemCategoryLinks;     property TableForItems: TnxTable read FTableForItems write FTableForItems;   end; 

TcmDataPanel is a (3rd generation) TFrame descendent. It’s not used directly, but rather multiple other compound components descend from it.

TcmDataConnector is a component which holds the database connection information for these other components.

I’m using ModelMaker, and am trying to implement an Observer pattern so that multiple ‘Data Panels’ can be automatically updated whenever the ‘Data Connector’ changes state.

Here’s my problem: I can’t seem to get around the ‘circular refernece’ problem, as each class uses the other in the Interface section. Putting the associated ‘uses’ reference in the Interface section doesn’t clear up the ‘Undeclared identifier’ issue, and putting them both in the same unit doesn’t either. Right now they are in the same unit (I’ve tried them in separate units, and together), and I get the ‘Undeclared identifier: TcmTPDataConnector’ error.

How can I get around this?

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UPDATE:

It’s Friday night at 9:30pm where I am, and I was totally stuck. Just MINUTES after my post, you people SAVED THE DAY!! (night!) THANK YOU!!

Man, I love StackOverflow…. SO my friend in this learning-like-crazy season. : ) Thank you, thank you, thank you…

Answer 1

On the same unit, try the following:

TcmTPDataConnector = class(TComponent);   TcmTPDataPanel = class(TcmTPBasePanel)    ...  end;  TcmTPDataConnector = class(TComponent)   ... end;