将对象数组从 C# 返回到 COM 中的 C

Posted 2023-02-22

【中文标题】将对象数组从 C# 返回到 COM 中的 C

【英文标题】：return array of object from C# to C in COM

【发布时间】：2013-04-30 06:56:03

【问题描述】：

我正在使用 COM 在 C++ 和 C# 之间进行通信。

我在 C# 中有以下类

电子邮件地址

/// <summary>
/// Email Address
/// </summary>
public class EmailAddress

    /// <summary>
    /// SMTP Address
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]        
    public string Address;

    /// <summary>
    /// Name
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string Name;

邮箱

/// <summary>
/// MailBox Entity
/// </summary>   
public struct MailBoxEntity

    /// <summary>
    /// SMTP Address
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string SMTPAddress;

    /// <summary>
    /// Mailbox Display Name
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string Name;

    /// <summary>
    /// Mailbox Server Name
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string sServerName;

EmailEntity（尚未实现将包含每个字段的属性的 IEmailEntity）

/// <summary>
/// Class for Email Entity
/// </summary>
public class EmailEntity : IEmailEntity

    /// <summary>
    /// BccRecipients
    /// </summary>
    [MarshalAs(UnmanagedType.ByValArray)]
    public EmailAddress[] BccRecipients;

    /// <summary>
    /// Body
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string Body;

    /// <summary>
    /// CcRecipients
    /// </summary>
    [MarshalAs(UnmanagedType.ByValArray)]
    public EmailAddress[] CcRecipients;

    /// <summary>
    /// Culture
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string Culture;

    /// <summary>
    /// DateTimeCreated
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string DateTimeCreated;

    /// <summary>
    /// DateTimeReceived
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string DateTimeReceived;

    /// <summary>
    /// DateTimeSent
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string DateTimeSent;

    /// <summary>
    /// FromAddress
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string FromAddress;

    /// <summary>
    /// FromName
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string FromName;


    /// <summary>
    /// HasAttachments
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string HasAttachments;

    /// <summary>
    /// Id
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string Id;

    /// <summary>
    /// Importance
    /// </summary>
   [MarshalAs(UnmanagedType.BStr)]
    public string Importance;

    /// <summary>
    /// LastModifiedName
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string LastModifiedName;

    /// <summary>
    /// LastModifiedTime
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string LastModifiedTime;

    /// <summary>
    /// MimeContent
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string MimeContent;

    /// <summary>
    /// ParentFolderId
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string ParentFolderId;

    /// <summary>
    /// Original Mailbox
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public MailBoxEntity OriginalMailBox;


    /// <summary>
    /// ParentFolderName
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string ParentFolderName;

    /// <summary>
    /// ReceivedByAddress
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string ReceivedByAddress;

    /// <summary>
    /// ReceivedByName
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string ReceivedByName;

    /// <summary>
    /// Size
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string Size;

    /// <summary>
    /// Subject
    /// </summary>
    [MarshalAs(UnmanagedType.BStr)]
    public string Subject;

    /// <summary>
    /// ToRecipients
    /// </summary>
    [MarshalAs(UnmanagedType.ByValArray)]
    public EmailAddress[] ToRecipients;

如何访问从 C# 中的函数返回的 EmailEnity 对象数组（在 C++ 中） 并阅读 EmailEntity 类的字段。请注意，EmailEntity 类包含像这样的成员 EmailAddress[] 本身是一个对象数组。 我计划实现接口 IEmailEntity，其中包含访问 EmailEntity 字段的属性 并使用它来访问 C++ 中的字段。这样做对吗？

如何在 C++ 中访问复杂的字段成员，例如 EmailAddress (EmailAddress[] ToRecipients) 的数组。

请提出建议。

谢谢

【参考方案1】：

您可以像这样简化 .NET 代码（删除所有应该自动完成的 MarshalAs）：

[ComVisible(true)]
public class MyRootClass : IMyRootClass // some class to start with

    public IEmailEntity[] GetEntities()
    
        List<IEmailEntity> list = new List<IEmailEntity>();
        for(int i = 0; i < 10; i++)
        
            EmailEntity entity = new EmailEntity();
            List<IEmailAddress> addresses = new List<IEmailAddress>();
            addresses.Add(new EmailAddress  Name = "Joe" + i );
            entity.BccRecipients = addresses.ToArray();
            entity.Body = "hello world " + i;
            list.Add(entity);
        
        return list.ToArray();
       


[ComVisible(true)]
public interface IMyRootClass

    IEmailEntity[] GetEntities();


public class EmailEntity : IEmailEntity

    public IEmailAddress[] BccRecipients  get; set; 
    public string Body  get; set; 


public class EmailAddress : IEmailAddress

    public string Address  get; set; 
    public string Name  get; set; 


[ComVisible(true)]
public interface IEmailAddress

    string Address  get; set; 
    string Name  get; set; 


[ComVisible(true)]
public interface IEmailEntity

    IEmailAddress[] BccRecipients  get; set; 
    string Body  get; set; 
    // to be continued...

要将它与 C++ 一起使用，您需要注册 DLL 并构建一个 .TLB（类型库文件），如此处类似答案中所述：Implement a C# DLL COM File In Unmanaged C++ Program

然后，您可以在 C++ 中访问这些类，如下所示：

#include "stdafx.h"
#import  "c:\MyPathToTheTlb\YourAssembly.tlb" // import the COM TLB

using namespace YourAssembly;

int _tmain(int argc, _TCHAR* argv[])

  CoInitialize(NULL);
  IMyRootClassPtr ptr(__uuidof(MyRootClass));
  CComSafeArray<IUnknown*> entities = ptr->GetEntities(); // CComSafeArray needs atlsafe.h in the PCH
  for(int i = entities.GetLowerBound(0); i <= entities.GetUpperBound(0); i++)
  
    IEmailEntityPtr entity;
    entities.GetAt(i).QueryInterface(&entity);
    _bstr_t body = entity->Body;
    printf("%S\n", body.GetBSTR());

    CComSafeArray<IUnknown*> recipients = entity->BccRecipients;
    for(int j = recipients.GetLowerBound(0); j <= recipients.GetUpperBound(0); j++)
    
      IEmailAddressPtr address;
      recipients.GetAt(j).QueryInterface(&address);
      _bstr_t name = address->Name;
      printf(" %S\n", name.GetBSTR());
    
  
  CoUninitialize();

【讨论】：

您需要使用 [InterfaceType] 属性才能使此代码正常工作。目前，接口只能通过后期绑定访问，默认为 ComInterfaceType.InterfaceIsIDispatch。

@HansPassant - 此代码可以正常工作。我相信默认是双重的。

你说得对，把我染成紫色。看起来我必须在这里和那里编辑一些答案:(

调试断言失败。 atlsafe.h 中的表达式 psaSrc!=0 。是否因为正在返回 null entity->BccRecepients

这可能会发生，具体取决于您实际返回的内容。我的示例代码在 BccRecipients 中放置了一个数组，所以我不会得到 NULL。