Question

In Delphi, I want to be able to create an private object that’s associated with a class, and access it from all instances of that class. In Java, I’d use:

public class MyObject {     private static final MySharedObject mySharedObjectInstance = new MySharedObject(); } 

Or, if MySharedObject needed more complicated initialization, in Java I could instantiate and initialize it in a static initializer block.

(You might have guessed… I know my Java but I’m rather new to Delphi…)

Anyway, I don’t want to instantiate a new MySharedObject each time I create an instance of MyObject, but I do want a MySharedObject to be accessible from each instance of MyObject. (It’s actually logging that has spurred me to try to figure this out – I’m using Log4D and I want to store a TLogLogger as a class variable for each class that has logging functionality.)

What’s the neatest way to do something like this in Delphi?

Answer 1

Here is how I’ll do that using a class variable, a class procedure and an initialization block:

unit MyObject;  interface  type  TMyObject = class    private      class var FLogger : TLogLogger;    public      class procedure SetLogger(value:TLogLogger);      class procedure FreeLogger;    end;  implementation  class procedure TMyObject.SetLogger(value:TLogLogger); begin   // sanity checks here   FLogger := Value; end;  class procedure TMyObject.FreeLogger; begin   if assigned(FLogger) then      FLogger.Free; end;  initialization   TMyObject.SetLogger(TLogLogger.Create); finalization   TMyObject.FreeLogger; end.