教程-Supports判断接口(Instance)是否支持

 function TCommandEnabledController.GetCommandVisible(const ACommandName: string): Boolean;
 var
   I: Integer;
   //定义接口接收者
   oCommandVisibleExecutor: ICommandVisibleExecutor;
 begin
   Result := True;
   for I :=  to FExecutors.Count -  do
   begin
     //判断接口是否支持
     if Supports(FExecutors[I], ICommandVisibleExecutor, oCommandVisibleExecutor) then
     begin
       //使用接口接收者
       if not oCommandVisibleExecutor.CommandVisible(ACommandName) then
       begin
         Result := False;
         Break;
       end;
     end;
   end;
 end;

delphi中的函数Supports位于SysUtils单元

定义如下：

 { Interface support routines }

 function Supports(const Instance: IInterface; const IID: TGUID; out Intf): Boolean; overload;
 function Supports(const Instance: TObject; const IID: TGUID; out Intf): Boolean; overload;
 function Supports(const Instance: IInterface; const IID: TGUID): Boolean; overload;
 function Supports(const Instance: TObject; const IID: TGUID): Boolean; overload;
 function Supports(const AClass: TClass; const IID: TGUID): Boolean; overload;

实现如下：

 { Interface support routines }

 function Supports(const Instance: IInterface; const IID: TGUID; out Intf): Boolean;
 begin
   Result := (Instance <> nil) and (Instance.QueryInterface(IID, Intf) = );
 end;

 function Supports(const Instance: TObject; const IID: TGUID; out Intf): Boolean;
 var
   LUnknown: IUnknown;
 begin
   Result := (Instance <> nil) and
             ((Instance.GetInterface(IUnknown, LUnknown) and Supports(LUnknown, IID, Intf)) or
              Instance.GetInterface(IID, Intf));
 end;

 function Supports(const Instance: IInterface; const IID: TGUID): Boolean;
 var
   Temp: IInterface;
 begin
   Result := Supports(Instance, IID, Temp);
 end;

 function Supports(const Instance: TObject; const IID: TGUID): Boolean;
 var
   Temp: IInterface;
 begin
   Result := Supports(Instance, IID, Temp);
 end;

 function Supports(const AClass: TClass; const IID: TGUID): Boolean;
 begin
   Result := AClass.GetInterfaceEntry(IID) <> nil;
 end;