How to cast a Interface to a Object in Delphi

Question

In delphi 2009 I have a reference to a IInterface which I want to cast to the underlying TObject

Using TObject(IInterface) obv

Answer 1

There is a nice alternative when you know the implementing object is a TComponent descendant.

You can use the IInterfaceComponentReference interface, which is defined up in Classes unit:

IInterfaceComponentReference = interface
  ['{E28B1858-EC86-4559-8FCD-6B4F824151ED}']
  function GetComponent: TComponent;
end;

And then it's declared in TComponent (and implemented to return self):

  TComponent = class(TPersistent, IInterface, IInterfaceComponentReference)

So if you know the implementing object is a TComponent then you can do this:

function InterfaceToComponent(const AInterface: IInterface): TComponent;
var
  vReference: IInterfaceComponentReference;
begin
  if Supports(AInterface, IInterfaceComponentReference, vReference) then
    result := vReference.GetComponent
  else
    result := nil;
end;