Calling a method in main app from dll - delphi

Question

Can I call a method which is placed in main application from dll code?

Answer 1

seems there is only one way to do it - create a callback object.
in your application you have to declare interface, wich describes your method, for example:
IMyMethodInterface = interface(IInterface)
procedure MyMethod(); stdcall;
end;
next you have to create class, wich implements this interface (and your method):
TMyMethodObject = class(TInterfacedObject, IMyMethodInterface)
public
procedure MyMethod(); stdcall;
end;
when you load DLL, you have to create TMyMethodObject instance and pass its IMyMethodInterface to dll; of course dll has to have corresponding method and export it (wich takes interface as parameter) SetMethodCallback wich stores interface reference:
vars:
var mmo : IMyMethodInterface;
dllHandle : THandle;
smc : procedure (mmi : IMyMethodInterface); stdcall;
code:
mmo := TMyMethodObject.Create();
dllHandle := LoadLibrary('mydll.dll');
smc := GetProcAddress(dllHandle, 'SetMethodCallback');
if assigned(smc) then
smc(mmo);
now, you can use IMyMethodInterface reference in your dll to call method.
of course you can statically link dll and use it directly:
procedure SetMethodInteface(mmi : IMyMethodInterface); stdcall; external 'mydll.dll';
here is an DLL sample code:
library Project3;
// uses YourMethodIntf.pas
{$R *.res}
var AppMethod : IMyMethodInterface;
procedure SetAppMethodCallback(mmi : IMyMethodInterface); stdcall;
begin
AppMethod := mmi;
end;
procedure AnotherDllMethod();
begin
//here you can use AppMethod.MyMethod();
end;
exports
SetAppMethodCallback name 'SetMethodcallback';
begin
end.
take into account that your mmo object (TMyMethodInterface) will not be destroyed until you set AppMethod in dll to nil (or FreeLibrary dll ), so be careful