delphi - 我可以将 Base 类型转换为 Derived 接口(interface)类型吗？

Question

我可以将基本接口(interface)类型转换为派生接口(interface)吗？

我怎样才能像德尔福一样

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类当前未实现 IDerived , 它只实现 IBase .
您的 TDerived类同时实现 IBase (通过继承 TBase )和 IDerived (明确)。

你应该要么

更改您的 TBase声明
TBase =class(TInterfacedObject,IBase, IDerived)
并实现 IDerived TBase 中的方法.

或更改 b:=TBase.Create;至b:=TDerived.Create ;