Question

I have two components A and B. Component B derives from component A and shares most properties and procedures with it. Now I have a lengthy procedure like this:

procedure DoSomething;
begin
  Form1.Caption := Component_A.Caption;
  // hundreds of additional lines of code calling component A
end;

Depending on whether component B is active or not, I would like to reuse the above procedure and replace the Component_A part with the name of component B. It should look like this then:

procedure DoSomething;
var
  C: TheComponentThatIsActive;
begin
  if Component_A.Active then
    C := Component_A;
  if Component_B.Active then
    C := Component_B;
  Form1.Caption := C.Caption;
end;

How can I do that in Delphi2007?

Thanks!

Answer 1

TheComponentThatIsActive should be the same type that ComponentA is (TComponentA).

Now, if you run into a stumbling block where some properties/methods only belong to ComponentB, then check and typecast it.

procedure DoSomething;
var
    C: TComponentA;

begin
    if Component_A.Active then
        C := Component_A
    else if Component_B.Active then
        C := Component_B
    else
        raise EShouldNotReachHere.Create();

    Form1.Caption := C.Caption;

    if C=Component_B then
        Component_B.B_Only_Method;
end;