我可以将 Base 类型转换为 Derived 接口类型吗？

Question

我可以将基接口类型转换为派生接口吗？

我怎样才能像Delphi一样

Delphi 生成代码/Delphi 7：

function TXMLBook.Get_Id: IXMLId;
begin
   Result := ChildNodes['id'] as IXMLId;
end;

ChildNodes['id'] 是基本类型 IXMLNode

IXMLId 是从 IXMLNode 派生的类型

我的示例代码是：

type
IBase = interface(IInterface)
['{5CEA3668-36CB-444C-8D3E-06644070A2B4}']
  function Test:AnsiString;
end;

TBase =class(TInterfacedObject,IBase)
  function Test:AnsiString;
end;

IDerived =interface (IBase)
['{8CDB2982-43B0-4636-B6F5-2561C0D419A9}']
  function Test2: AnsiString;
end;

TDerived=class (TBase,IDerived)
  function Test:AnsiString;
  function Test2:AnsiString;
end;

{ TBase }

function TBase.Test: AnsiString;
begin
   Result:='Base Test';
end;

{ TDerived }

function TDerived.Test: AnsiString;
begin
  Result:='Derived Test';
end;

function TDerived.Test2: AnsiString;
begin
   Result:='Derived Test2';
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  b:IBase;
  d: IDerived;
begin
  b:=TBase.Create;
  d:=b as IDerived; // Error : Interface not supported 

  ShowMessage(b.Test);
end;

Answer 1

您的TBase 类目前没有实现IDerived，它只实现了IBase。 您的TDerived 类同时实现了IBase （通过从TBase 继承） 和IDerived （显式）。

你应该

1. 将您的 TBase 声明更改为

   TBase =class(TInterfacedObject,IBase, IDerived)

   并在TBase 中实现IDerived 方法。

2. 或将b:=TBase.Create;改为b:=TDerived.Create；