c# - 在 .NET 对象上设置 "nullable"属性

Question

我有一些 .NET 互操作代码，我在其中设法加载对象并读取属性，但是在设置对象的属性时遇到问题。以下是 Delphi 代码的相关部分:

uses
  mscorlib_TLB, Winapi.ActiveX;

type
  // Irrelevant parts of the code omitted
  TDotNetObject = class(TObject)
  private
    FTarget: OleVariant;
    FType: _Type;
  public
    procedure SetProperty(const APropertyName: string; const AValue: OleVariant; const AIndex: Integer = -1);
  end;

function VariantToPSafeArray(const AValue: Variant): PSafeArray;
begin
  Result := PSafeArray(VarArrayAsPSafeArray(AValue));
end;

procedure TDotNetObject.SetProperty(const APropertyName: string; const AValue: OleVariant; const AIndex: Integer = -1);
var
  LPropertyInfo: _PropertyInfo;
  LIndex: PSafeArray;
begin
  if AIndex >= 0 then
    LIndex := VariantToPSafeArray(VarArrayOf([AIndex]))
  else
    LIndex := nil;
  LPropertyInfo := FType.GetProperty(APropertyName, BindingFlags_Instance or BindingFlags_Public or BindingFlags_NonPublic);
  if LPropertyInfo <> nil then
    LPropertyInfo.SetValue(FTarget, AValue, LIndex);
end;

procedure UpdateDefectStatus(const ADefectID, AStatus: Integer);
var
  LObject: TDotNetObject;
begin
  // ** Code to obtain the object omitted ***
  LObject.SetProperty('Status', AStatus);
end;

mscorlib_TLB 单元来自 Project JEDI 中的 JCL，此处:

https://github.com/project-jedi/jcl/blob/master/jcl/source/windows/mscorlib_TLB.pas

在TDotNetObject.SetProperty中调用LPropertyInfo.SetValue时抛出错误:

Project TestProject.exe raised exception class EOleException with message 'Object of type 'System.Int32' cannot be converted to type 'System.Nullable`1[MTData.Transport.Tracking.DefectReporting.DefectStatus]''.

C# 对象上的 DefectStatus 属性声明为:

public DefectStatus? Status

(即可以为空)

C# 中的 Status 属性类型声明为:

public enum DefectStatus
{
    /// <summary>
    /// Defect Reported.
    /// </summary>
    Reported,
    /// <summary>
    /// Defect assessed.
    /// </summary>
    Assessed,
    /// <summary>
    /// Defect on work order.
    /// </summary>
    OnWorkOrder,
    /// <summary>
    /// Defect closed.
    /// </summary>
    Closed
}

我在这里找到了如何使用 C# 处理这种情况的解决方案:

https://stackoverflow.com/a/13270302/3164070

但是我对如何在 Delphi 中做同样的事情有点迷失。有什么想法吗？

编辑

鉴于 Olivier 的回答，我尝试编写一些 Delphi 代码来执行等效操作，如下所示:

procedure InvokeToObject;
var
  LType, LDefectStatusType: _Type;
  LInvokeFlags: TOleEnum;
  LArgs: PSafeArray;
  LValue: Integer;
  LResult: OleVariant;
  LRes: HRESULT;
  LResHex: string;
begin
  LType := MTDataClr.GetCoreType('System.Enum');
  LDefectStatusType := MTDataClr.GetType('MTData.Transport.Tracking.DefectReporting.DefectStatus');
  LInvokeFlags := BindingFlags_InvokeMethod or BindingFlags_Static;
  LValue := 1;
  LArgs := VariantToPSafeArray(VarArrayOf([LDefectStatusType, LValue]));
  LRes := LType.InvokeMember_2('ToObject', LInvokeFlags, nil, Null, LArgs, nil, LResult);
  LResHex := IntToHex(LRes);
end;

这段代码的目标只是调用 Enum 类型的 ToObject 方法。获取LType和LDefectStatusType成功，但是调用InvokeMember_2没有成功，返回码为:0x80131512，这显然是Missing Member异常。关于我做错了什么有什么想法吗？

Answer 1

问题在于枚举不是 int，这意味着 SetValue() 需要执行双重转换(Int32 到 DefectStatus > 和 DefectStatus 到 DefectStatus?)，但它不能(它只能执行一个)。

这是一个 C# 代码，可以重现您想要执行的操作:

using System;
using System.Reflection;

public enum DefectStatus
{
    Reported,
    Assessed,
    OnWorkOrder,
    Closed
}

public class Defect
{
    public DefectStatus? Status {get; set;}
}

public class Test
{
    public static void Main()
    {
        Defect def = new Defect();

        PropertyInfo pi = typeof(Defect).GetProperty("Status");

        // This throws an ArgumentException
//      pi.SetValue(def, 1, null);

        // Retrieve the Assessed enum via its numeric value
        object assessed = Enum.ToObject(typeof(DefectStatus), 1);

        // This works as expected
        pi.SetValue(def, assessed, null);

        Console.WriteLine(def.Status);
    }
}

因此您需要在 Delphi 中检索枚举。为此，您需要使用 API 来访问 Enum 类型并对其调用 ToObject。