How to store form method pointers in a TList

Problem/Question/Abstract:

What is the correct way to store form method pointers on a TList then use the TList items[] to call the various procedures?

Answer:

This isn't as easy as it seems. Despite the name, method pointers aren't pointers, they're 8-byte records (type TMethod, check the Help). So, you have to New a TMethod on the heap for each method pointer you want to store to the list, and of course free the records before you clear or free the list:


type
  TmyMethod = procedure(s: string) of object;
  TpMyMethod = ^TmyMethod;
  TpMethPtr = ^Tmethod;

procedure addMethodPointer(lst: TList; mp: TmyMethod);
var
  p: TpMethPtr;
begin
  new(p);
  p^ := Tmethod(mp);
  lst.add(p);
end;

procedure clearPointers(lst: TList);
var
  j: integer;
begin
  for j := 0 to lst.count - 1 do
  begin
    dispose(TpMethPtr(lst[j]));
  end;
end;


The fancy casting in addMethodPointer is so you can change the parameter type for mp without changing anything else.

The call to a given pointer goes this way:


TpMyMethod(lst[1])^(myString);