如何将_ComObject类型转换为本机类型，例如Long或其他类型（出现强制转换错误）？ [英] How do I convert type _ComObject to a native type like Long or other (getting cast error)?

问题描述

我试图通过调用

Principal.ExtensionGet("lastLogonTimestamp")

VB.NET代码：

<DirectoryProperty("lastLogonTimestamp")>
Public Property LastLogonTimestamp() As Date? ' no matter what this type is, I cannot cast the Object coming in
    Get
        Dim valueArray = ExtensionGet("lastLogonTimestamp")
        If valueArray Is Nothing OrElse valueArray.Length = 0 Then Return Nothing
        Return DateTime.FromFileTimeUtc(valueArray(0))
    End Get
    Set(value As Date?)
        ExtensionSet("lastLogonTimestamp", value)
    End Set
End Property

这将返回 Object （即 Object（））或 null 。麻烦在于它抱怨我对 Long 的转换（或其他我尝试过的类型： ULong ，日期和字符串）。它总是告诉我这样的情况：

This returns an array of Object (i.e. Object()) or null. The trouble is it complains about my cast to Long (or other types I have tried like: ULong, Date, and String). It always tells me something like this:

从'_ComObject'类型到'Long'类型的转换无效。

Conversion from type '_ComObject' to type 'Long' is not valid.

在一个新问题，我着手进行另一种选择（从DateTime到64位）

In a new question, I set out to go the other way (from DateTime to 64 bit)

推荐答案

使用中提供的C＃代码链接（通过HansPassant的注释），我使用以下VB代码解决了此问题：

Using C# code provided in link via HansPassant's comment below, I resolved this with the following VB code:

<DirectoryProperty("lastLogonTimestamp")>
Public Property LastLogonTimestamp() As Date?
    Get
        'Dim valueArray = GetProperty("whenChanged")
        Dim valueArray = ExtensionGet("lastLogonTimestamp") 'ExtensionGet("LastLogon")
        If valueArray Is Nothing OrElse valueArray.Length = 0 Then Return Nothing

        Dim lastLogonDate = valueArray(0)
        Dim lastLogonDateType = lastLogonDate.GetType()
        Dim highPart = CType(lastLogonDateType.InvokeMember("HighPart", Reflection.BindingFlags.GetProperty, Nothing, lastLogonDate, Nothing), Int32)
        Dim lowPart = CType(lastLogonDateType.InvokeMember("LowPart", Reflection.BindingFlags.GetProperty Or Reflection.BindingFlags.Public, Nothing, lastLogonDate, Nothing), Int32)
        Dim longDate = CLng(highPart) << 32 Or (CLng(lowPart) And &HFFFFFFFFL)
        Dim result = IIf(longDate > 0, CType(DateTime.FromFileTime(longDate), DateTime?), Nothing)

        Return result
        'Return DateTime.FromFileTimeUtc(valueArray(0))
    End Get
    Set(value As Date?)
        ExtensionSet("lastLogonTimestamp", value)
    End Set
End Property

和C＃版本（从源）：

[DirectoryProperty("RealLastLogon")]
public DateTime? RealLastLogon
{
    get
    {
        if (ExtensionGet("LastLogon").Length > 0)
        {
            var lastLogonDate = ExtensionGet("LastLogon")[0];
            var lastLogonDateType = lastLogonDate.GetType();
            var highPart = (Int32)lastLogonDateType.InvokeMember("HighPart", BindingFlags.GetProperty, null, lastLogonDate, null);
            var lowPart = (Int32)lastLogonDateType.InvokeMember("LowPart", BindingFlags.GetProperty | BindingFlags.Public, null, lastLogonDate, null);

            var longDate = ((Int64)highPart << 32 | (UInt32)lowPart);

            return longDate > 0 ? (DateTime?) DateTime.FromFileTime(longDate) : null;
        }

        return null;
    }
}

这篇关于如何将_ComObject类型转换为本机类型，例如Long或其他类型（出现强制转换错误）？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！