Hello,

Sorry for the poor title,I'm new to OOP so I don't know what is the term for what I need to do.

I have, say, 10 different Objects that inherit one Object.They have different amount and type of class members,but all of them have one property in common - Visible.

type
  TObj1=class(TObject)
  private 
    a:integer;
    ...(More members)
    Visible:Boolean;
end;
  TObj2=class(TObject)
  private 
    b:String;
    ...(More members)
    Visible:Boolean;
end;

...(Other 8 objects)

For each of them I have a variable.

var Obj1:TObj1;
    Obj2:TObj2;
    Obj3:TObj3;
    ....(Other 7 objects)

Rule 1: Only one object can be initialized at a time(others have to be freed) to be visible.

For this rule I have a global variable

var CurrentVisibleObj:TObject; //Because they all inherit TObject

Finally there is a procedure that changes visibility.

procedure ChangeObjVisibility(newObj:TObject);
begin
  CurrentVisibleObj.Free; //Free the old object
  CurrentVisibleObj:=newObj; //assign the new object
  CurrentVisibleObj:= ??? //Create new object
  CurrentVisibleObj.Visible:=true; //Set visibility to new object
end;

There is my problem,I don't know how to initialize it,because the derived class is unknown.

How do I do this?

I simplified the explanation,in the project there are TFrames each having different controls and I have to set visible/not visible the same way(By leaving only one frame initialized).

Sorry again for the title,I'm very new to OOP.