In Delphi is it possible to bind an interface to an object that doesn't implement it

Question

I know Delphi XE2 has the new TVirtualInterface for creating implementations of an interface at runtime. Unfortunately I am not using XE2 and I\'m wondering what kind of hackery

Answer 1

I'm not sure, what you want to accomplish and why you want to dynamically bind that interface, but here is a way to do it (don't know if it fits your need):

type
  IMyInterface = interface
  ['{8A827997-0058-4756-B02D-8DCDD32B7607}']
    procedure Go;
  end;

  TMyClass = class(TInterfacedObject, IInterface)
  private
    FEnabled: Boolean;
  protected
    property Enabled: Boolean read FEnabled;
  public
    constructor Create(AEnabled: Boolean);
    function QueryInterface(const IID: TGUID; out Obj): HResult; stdcall;
    procedure Go; //I want to dynamically bind IMyInterface.Go here
  end;

  TMyInterfaceWrapper = class(TAggregatedObject, IMyInterface)
  private
    FMyClass: TMyClass;
  protected
    property MyClass: TMyClass read FMyClass implements IMyInterface;
  public
    constructor Create(AMyClass: TMyClass);
  end;

constructor TMyInterfaceWrapper.Create(AMyClass: TMyClass);
begin
  inherited Create(AMyClass);
  FMyClass := AMyClass;
end;

constructor TMyClass.Create(AEnabled: Boolean);
begin
  inherited Create;
  FEnabled := AEnabled;
end;

procedure TMyClass.Go;
begin
  ShowMessage('Go');
end;

function TMyClass.QueryInterface(const IID: TGUID; out Obj): HResult;
begin
  if Enabled and (IID = IMyInterface) then begin
    IMyInterface(obj) := TMyInterfaceWrapper.Create(Self);
    result := 0;
  end
  else begin
    if GetInterface(IID, Obj) then
      Result := 0
    else
      Result := E_NOINTERFACE;
  end;
end;

And this is the corresponding test code:

var
  intf: IInterface;
  my: IMyInterface;
begin
  intf := TMyClass.Create(false);
  if Supports(intf, IMyInterface, my) then
    ShowMessage('wrong');

  intf := TMyClass.Create(true);
  if Supports(intf, IMyInterface, my) then
    my.Go;
end;