Passing an Object as an Interface
This should be a simple answer, i believe its going to be a no,
but taken from a larger project, i have an interface and the procedureiMyUnknown= interface(IInterface)
['..GUID..']
end;
procedure WorkObject(iObj :iMyUnknown);
i know this works
var
MyU开发者_运维知识库nknown : iMyUnknown;
begin
if supports(obj, iMyUnknown, MyUnknown) then
WorkObject(MyUnknown);
But is it possible to do something like this?
if supports(obj, iMyUnknown) then
WorkObject(obj as iMyUnknown);
Why would you need to cast?
If obj supports the interface, and all you need to do is check that before passing it to a procedure, you can simply pass the object itself. The compiler will take care of the rest. You only need the third param on the Supports call if you want to access methods of the interface.
Compile and run the code below. It should compile without errors and present you with a console window and a dialog message.
program Project1;
{$APPTYPE CONSOLE}
uses
Classes
, Dialogs
, SysUtils
;
type
iMyUnknown = interface(IInterface)
['{DA867EBA-8213-4A91-8E03-1AACA150CE77}']
procedure DoSomething;
end;
TMuster = class(TInterfacedObject, iMyUnknown)
procedure DoSomething;
end;
procedure WorkObject(iObj: iMyUnknown);
begin
if Assigned(iObj) then ShowMessage('Got something');
end;
{ TMuster }
procedure TMuster.DoSomething;
begin
beep;
end;
var
obj: TMuster;
begin
try
obj := TMuster.Create;
if Supports(obj, iMyUnknown) then
WorkObject(obj);
except
on E:Exception do
Writeln(E.Classname, ': ', E.Message);
end;
end.
Yes, you can. The as
operator worked with interfaces ever since the support for interfaces has been added to the language (around Delphi 3, IIRC). The code you posted works. Where is the problem?
You can cast an object to an interface with an as-cast, as long as the compiler knows that your object supports IInterface, and your interface has a GUID. So it won't work with TObject, but with TInterfacedObject it will.
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