我从.NET类库中获取IEnumVariant,我正在尝试使用泛型类将其转换为IEnumerator
存在编译器错误,"运算符不适用于此操作数类型"当试图将IInterface强制转换为泛型类型T. 我在尝试将类型转换为类时遇到过变通方法,但这些不适用于接口。
Rob建议使用Supports似乎有问题,TypeInfo也为参数化类型返回nil。
uses WinApi.ActiveX, Generics.Collections;
type
TDotNetEnum<T: IInterface> = class(TInterfacedObject, IEnumerator<T>)
strict private
FDotNetEnum: IEnumVariant;
FCurrent: T;
function MoveNext: Boolean;
procedure Reset;
function GetCurrent: TObject;
function IEnumerator<T>.GetCurrent = GenericGetCurrent;
function GenericGetCurrent: T;
public
constructor Create(const ADotNetObject: OleVariant);
//// I can get it to work using this constructor
// constructor Create(const ADotNetObject: OleVariant; const AGUID: TGUID);
end;
implementation
uses System.Rtti, SysUtils, mscorlib_TLB, ComObj;
constructor TDotNetEnum<T>.Create(const ADotNetObject: OleVariant);
var
netEnum: IEnumerable;
begin
netEnum := IUnknown(ADotNetObject) as mscorlib_TLB.IEnumerable;
FDotNetEnum := netEnum.GetEnumerator();
end;
function TDotNetEnum<T>.GenericGetCurrent: T;
begin
result := FCurrent;
end;
function TDotNetEnum<T>.GetCurrent: TObject;
begin
result := nil;
end;
function TDotNetEnum<T>.MoveNext: Boolean;
var
rgvar: OleVariant;
fetched: Cardinal;
ti: TypeInfo;
guid: TGUID;
begin
OleCheck(FDotNetEnum.Next(1, rgvar, fetched));
result := fetched = 1;
if not result then
FCurrent := nil
else
begin
FCurrent := IUnknown(rgvar) as T; // <-- Compiler error here
//// Doesn't work using Supports either
// ti := TypeInfo(T); // <-- returns nil
// guid := GetTypeData(@ti)^.Guid;
// Supports(IUnknown(rgvar), guid, FCurrent);
end;
end;
procedure TDotNetEnum<T>.Reset;
begin
OleCheck(FDotNetEnum.Reset);
end;
我是否遗漏了某些内容以使通用接口类型能够起作用?
我确实有替代构造函数,我可以从中获取guid
TDotNetEnum<IContact>.Create(vContactList, IContact);
工作但理想
TDotNetEnum<IContact>.Create(vContactList);
没有按&#39;吨
答案 0 :(得分:6)
使用as
转换接口仅对具有GUID的接口有效。编译器在编译泛型类时不能假定T
具有GUID,因此它不能接受val as T
形式的表达式。
This has been covered before, but in reference to the Supports
function,与as
运算符具有相同的限制。
解决方案是使用RTTI获取接口的GUID,然后使用它来输入接口值。您可以使用Supports
:
guid := GetTypeData(TypeInfo(T))^.Guid;
success := Supports(IUnknown(rgvar), guid, FCurrent);
Assert(success);
您也可以直接致电QueryInterface
:
guid := GetTypeData(TypeInfo(T))^.Guid;
OleCheck(IUnknown(rgvar).QueryInterface(guid, FCurrent));