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.net 如何通过反射检索字符串并将其连接起来

.net vb.net string

.net 如何通过反射检索字符串并将其连接起来,.net,vb.net,string,.net,Vb.net,String,我有一个长字符串，使用以下模式将其划分为许多较小的字符串： Public Class Test Public Prefix_1 as String = "1 to 100 bytes" Public Prefix_2 as String = "101 to 200 bytes" Public Prefix_3 as String = "201 to 300 bytes" Public Prefix_4 as String = "301 to 400 bytes"

我有一个长字符串，使用以下模式将其划分为许多较小的字符串：

Public Class Test
    Public Prefix_1 as String = "1 to 100 bytes"
    Public Prefix_2 as String = "101 to 200 bytes"
    Public Prefix_3 as String = "201 to 300 bytes"
    Public Prefix_4 as String = "301 to 400 bytes"
    'and so on
End Class
这个
测试类
已编译为类库项目（即.dll文件），并保存到C:\Test.dll

请注意，我事先不知道dll文件中存在多少
前缀
字符串

我的问题是：如何通过反射检索以
前缀开头的所有字符串
，并将其升序连接（即前缀1和前缀2…）为单个字符串

赏金更新：

奖励仅适用于VB.NET解决方案中的答案

您有公共字段，因此，从表示类的
类型
对象获取
字段信息
对象，并排除名称不以
前缀开头的对象

一旦有了这些，您就可以调用
FieldInfo
对象上的
GetValue
，将对象（类
Test
的实例）作为参数来获取字段的值

如果您需要按顺序排列结果，那么我建议使用LINQ语句

对不起，我不懂VB，否则我会给你写一些代码

更新：一些C#代码

应该就这些了。

这应该让你开始了。抱歉，这是C#，但我不记得lambda语法

     Type type = Assembly.LoadFrom (@"c:\test.dll").GetType ("Test");
     object instance = type.GetConstructor (Type.EmptyTypes).Invoke (null);
     var fields = type.GetFields ().Where (f => f.Name.StartsWith ("Prefix_")).OrderBy(f => f.Name);
     string x = fields.Aggregate (new StringBuilder (), (sb, f) => sb.Append((string)f.GetValue (instance)), sb => sb.ToString ());
VB.NET

  Dim type As Type = Assembly.LoadFrom("c:\test.dll").GetType("Test")
  Dim instance As Object = Type.GetConstructor(Type.EmptyTypes).Invoke(Nothing)
  Dim fields = _
     type.GetFields() _
        .Where(Function(f) f.Name.StartsWith("Prefix_")) _
        .OrderBy(Function(f) f.Name)
  Dim bigString As String = _
     fields.Aggregate(New StringBuilder(), _
                      Function(sb, f) sb.Append(DirectCast(f.GetValue(instance), String)), _
                      Function(sb) sb.ToString())
是用C代码编写的（VB.NET有点生疏了：）：

我想根据您的回答，按照您的要求，用Visual Basic提出一个面向对象的解决方案

免责声明：

请记住，我不是VB.NET开发人员。我提供的代码经过测试并正在运行，但肯定需要一些特定于语言的改进

我假设您正在使用类
Test
的实例，因为它公开的字段不是
共享的

主旨

通过分析您的需求，我发现这对于：

  • 将所有字段的命名策略集中在一个位置，以使您的解决方案可维护
  • 注意字段的排序。如果您有前缀_1、前缀_2和前缀_11，则可能会以错误的方式进行排序：前缀_1、前缀_11和前缀_2
  • 验证是否没有缺少字段名（即从前缀_1跳到前缀_3）
根据您的要求，我在一个名为
StringChunkField
的类中对每个包含字符串块的字段进行建模。 该类为每个包含字符串块的前缀字段建模，并承担以下职责：

  • 提供有关字段本身的信息：名称、编号、包含的字符串块以及其中的字符数
  • 集中有关用于命名字段的格式和编号的信息。这里定义了要查找的前缀，并且在处的数字以字段名称开始
  • 从上一项中，它可以回答字段是否是字符串开头的字段，以及字段是否是StringChunkField
  • 实现IComparable以将排序逻辑集中在一个位置（基于字段编号）

现在，我们已经定义了什么是
StringChunkField
、使用什么名称前缀以及如何构建前缀，我们可以通过
TypeEmbeddedStringReader
类的实例查询对象中包含的字符串

其责任是：

  • 查找对象中显示的所有
    StringChunkFields
  • 验证找到的字段编号是否根据
    StringChunkField
    中定义的基数开始，以及编号是否连续
  • 从
    StringChunkField
    s值重建对象中嵌入的字符串

    Imports System.Reflection
Imports System.Text

Public Class TypeEmbeddedStringReader

    Public Shared Function ReadStringFrom(ByRef target As Object) As String
        ' Get all prefix fields from target
        ' Each StringChunkField hold a chunk of the String to rebuild
        Dim prefixFields As IEnumerable(Of StringChunkField) = GetPrefixFieldsFrom(target)

        ' There must be, at least, one StringChunkField
        ValidateFieldsFound(prefixFields)
        ' The first StringChunkField must hold the beggining of the string (be numbered as one)
        ValidateFieldNumbersBeginAtOne(prefixFields)
        ' Ensure that no StringChunkField number were skipped
        ValidateFieldNumbersAreConsecutive(prefixFields)

        ' Calculate the total number of chars of the string to rebuild to initialize StringBuilder and make it more efficient
        Dim totalChars As Integer = CalculateTotalNumberOfCharsIn(prefixFields)
        Dim result As StringBuilder = New StringBuilder(totalChars)

        ' Rebuild the string
        For Each field In prefixFields
            result.Append(field.StringChunk)
        Next

        ' We're done
        Return result.ToString()
    End Function

#Region "Validation"

    Private Shared Sub ValidateFieldsFound(ByVal fields As List(Of StringChunkField))
        If (fields.Count = 0) Then Throw New ArgumentException("Does not contains any StringChunkField", "target")
    End Sub

    Private Shared Sub ValidateFieldNumbersBeginAtOne(ByVal fields As List(Of StringChunkField))
        ' Get the first StringChunkField found
        Dim firstStringChunkField As StringChunkField = fields.First

        ' If does not holds the begining of the string...
        If (firstStringChunkField.HoldsBeginingOfTheString() = False) Then
            ' Throw an exception with a meaningful error message
            Dim invalidFirstPrefixField = String.Format("The first StringChunkField found, '{0}', does not holds the beggining of the string. If holds the beggining of the string, it should be numbered as '{1}'.", firstStringChunkField.Name, StringChunkField.BeginningOfStringFieldNumber)
            Throw New ArgumentException(invalidFirstPrefixField, "target")
        End If
    End Sub

    Private Shared Sub ValidateFieldNumbersAreConsecutive(ByVal fields As List(Of StringChunkField))
        For index = 0 To fields.Count - 2
            ' Get the current and next field in fields
            Dim currentField As StringChunkField = fields(index)
            Dim nextField As StringChunkField = fields(index + 1)

            ' If the numbers are consecutive, continue checking
            If (currentField.IsFollowedBy(nextField)) Then Continue For

            ' If not, throw an exception with a meaningful error message
            Dim missingFieldMessage As String = String.Format("At least one StringChunkField between '{0}' and '{1}' is missing", currentField.Name, nextField.Name)
            Throw New ArgumentException(missingFieldMessage, "target")
        Next
    End Sub

#End Region

    Private Shared Function CalculateTotalNumberOfCharsIn(ByVal fields As IEnumerable(Of StringChunkField)) As Integer
        Return fields.Sum(Function(field) field.NumberOfCharacters)
    End Function

    Private Shared Function GetPrefixFieldsFrom(ByVal target As Object) As List(Of StringChunkField)
        ' Find all fields int the target object
        Dim fields As FieldInfo() = target.GetType().GetFields()
        ' Select the ones that are PrefixFields 
        Dim prefixFields As IEnumerable(Of StringChunkField) = From field In fields Where StringChunkField.IsPrefixField(field) Select New StringChunkField(field, target)
        ' Return the sorted list of StringChunkField found
        Return prefixFields.OrderBy(Function(field) field).ToList()

    End Function
End Class
用法

我准备了一些示例类型来测试
TypeEmbeddedStringReader
类的行为和使用方法。 简单地说，您必须调用
Shared
函数
ReadStringFrom
作为参数传递包含要读取的字符串的对象

以下是示例类型：

    Public Class SampleType
        Public Prefix_1 As String = "1 to 100 bytes"
        Public Prefix_2 As String = "101 to 200 bytes"
        Public Prefix_3 As String = "201 to 300 bytes"
        Public Prefix_4 As String = "301 to 400 bytes"
    End Class

    Public Class TypeWithoutString

    End Class

    Public Class TypeWithNonConsecutiveFields
        Public Prefix_1 As String = "1 to 100 bytes"
        Public Prefix_5 As String = "101 to 200 bytes"
    End Class

    Public Class TypeWithInvalidStringBeginning
        Public Prefix_2 As String = "1 to 100 bytes"
    End Class
下面是我用来测试它的主要模块：

    Imports TypeEmbeddedStringReader.Samples

    Module Module1
        Sub Main()
            ExtractStringFrom(New TypeWithoutString())
            ExtractStringFrom(New TypeWithInvalidStringBeginning())
            ExtractStringFrom(New TypeWithNonConsecutiveFields())
            ExtractStringFrom(New SampleType())
        End Sub

        Private Sub ExtractStringFrom(ByVal target As Object)
            Try
                Dim result As String = TypeEmbeddedStringReader.ReadStringFrom(target)
                Console.WriteLine(result)
            Catch exception As ArgumentException
                Console.WriteLine("Type '{0}': {1}", target.GetType(), exception.Message)
            End Try
            Console.WriteLine()
        End Sub
    End Module
以及运行它的结果：

    Type 'TypeEmbeddedStringReader.Samples.TypeWithoutString': Does not contains any StringChunkField
    Parameter name: target

    Type 'TypeEmbeddedStringReader.Samples.TypeWithInvalidStringBeginning': The first StringChunkField found, 'Prefix_2', does not holds the beggining of the string. If holds the beggining of the string, it should be numbered as '1'.
    Parameter name: target

    Type 'TypeEmbeddedStringReader.Samples.TypeWithNonConsecutiveFields': At least one StringChunkField between 'Prefix_1' and 'Prefix_5' is missing
    Parameter name: target

    1 to 100 bytes101 to 200 bytes201 to 300 bytes301 to 400 bytes
请让我知道是否为你工作，如果我可以为你提供任何其他帮助

更新

根据Gens的请求，我向
TypeEmbeddedStringReader
类添加了一个函数，用于从提供名称和程序集文件的类型实例中读取字符串：

    Public Shared Function ReadStringFromInstanceOf(ByRef assemblyFile As String, ByRef targetTypeName As String)
        Dim assembly As Assembly = assembly.LoadFrom(assemblyFile)
        Dim targetType As Type = assembly.GetType(targetTypeName)

        Dim target As Object = Activator.CreateInstance(targetType)

        Return ReadStringFrom(target)
    End Function
以下是我用于测试的样本类型：

    Public Class UnorderedFields
        Public Prefix_2 As String = "101 to 200 bytes"
        Public Prefix_4 As String = "301 to 400 bytes"
        Public Prefix_1 As String = "1 to 100 bytes"
        Public Prefix_3 As String = "201 to 300 bytes"
    End Class
下面是测试它的代码：

    Dim assemblyFile As String = Assembly.GetExecutingAssembly()
    Dim targetTypeName As String = "TypeEmbeddedStringDemo.UnorderedFields"
    Console.WriteLine(TypeEmbeddedStringReader.ReadStringFromInstanceOf(assemblyFile, targetTypeName))
这是上述代码的输出：

    1 to 100 bytes101 to 200 bytes201 to 300 bytes301 to 400 bytes
我希望这能帮助你解决你的问题。如果你还需要什么，请告诉我

更新2

回答Gens，Simon的解决方案不起作用的原因是因为正在对字段名进行比较。下面的示例排序失败（只是为了说明排序问题，而且它是无效的）

它给出：

    1 to 100 bytes**301 to 400 bytes**101 to 200 bytes201 to 300 bytes
正在修复比较器实现中使用数字而不是名称的问题：

    Public Function Compare(ByVal x As FieldInfo, ByVal y As FieldInfo) As Integer Implements IComparer(Of FieldInfo).Compare
        Dim xNumber = Integer.Parse(x.Name.Replace("Prefix_", String.Empty))
        Dim yNumber = Integer.Parse(y.Name.Replace("Prefix_", String.Empty))
        Return xNumber.CompareTo(yNumber)
    End Function
给出正确的结果：

    1 to 100 bytes101 to 200 bytes201 to 300 bytes301 to 400 bytes
希望有帮助。

如果字符串的定义顺序与问题中的顺序相同，您可以避免排序，下面是一个简单的VB.NET答案：

Public Function Extract() As String
    Dim type As Type = Assembly.LoadFrom("C:\test.dll").GetType("YourNamespace.Test")
    Dim instance As Object = Activator.CreateInstance(type)
    Dim sb As New StringBuilder
    Dim field As FieldInfo
    For Each field In type.GetFields
        If field.Name.StartsWith("Prefix_") Then
            sb.Append(field.GetValue(instance))
        End If
    Next
    Return sb.ToString
End Function
否则，这里有一个带有排序的函数：

Public Function Extract() As String
    Dim type As Type = Assembly.LoadFrom("c:\test.dll").GetType("YourNamespace.Test")
    Dim fields As New List(Of FieldInfo)
    Dim field As FieldInfo
    For Each field In type.GetFields
        If field.Name.StartsWith("Prefix_") Then
            fields.Add(field)
        End If
    Next

    fields.Sort(New FieldComparer)

    Dim sb As New StringBuilder
    Dim instance As Object = Activator.CreateInstance(type)
    For Each field In fields
        sb.Append(field.GetValue(instance))
    Next
    Return sb.ToString
End Function

Private Class FieldComparer
    Implements IComparer(Of FieldInfo)

    Public Function Compare(ByVal x As FieldInfo, ByVal y As FieldInfo) As Integer Implements IComparer(Of FieldInfo).Compare
        Return x.Name.CompareTo(y.Name)
    End Function
End Class
使用您的问题中稍微修改的测试类：

Public Class Test
  Public Prefix_15 As String = "501 to 600 bytes"
  Public Prefix_5 As String = "401 to 500 bytes"
  Public Prefix_1 As String = "1 to 100 bytes"
  Public Prefix_2 As String = "101 to 200 bytes"
  Public Prefix_3 As String = "201 to 300 bytes"
  Public Prefix_4 As String = "301 to 400 bytes"
End Class
运行以下功能：

Public Function GetPrefixString() As String
  Dim type As Type = Assembly.LoadFrom("C:\test.dll").GetType("Test.Test")
  Dim test As Object = Activator.CreateInstance(type)

  Dim fieldList As New List(Of String)
  For Each field As FieldInfo In _
                    From x In type.GetFields _
                    Where x.Name.StartsWith("Prefix_") _
                    Order By Convert.ToInt32(x.Name.Replace("Prefix_", String.Empty))
    fieldList.Add(field.GetValue(test))
  Next

  Return String.Join(String.Empty, fieldList.ToArray)
End Sub
产生以下结果：

1到100字节101到200字节201到 300字节301到400字节401到500 字节501到600字节

嗨，Gens！我刚刚发布了你问题的答案。根据您所说的，我假设您必须使用类测试的实例，因为它公开的字段不是共享的。是这样吗？如果没有，请告诉我，以便我可以更新我的答案。谢谢为什么？ 
Public Function Extract() As String
    Dim type As Type = Assembly.LoadFrom("C:\test.dll").GetType("YourNamespace.Test")
    Dim instance As Object = Activator.CreateInstance(type)
    Dim sb As New StringBuilder
    Dim field As FieldInfo
    For Each field In type.GetFields
        If field.Name.StartsWith("Prefix_") Then
            sb.Append(field.GetValue(instance))
        End If
    Next
    Return sb.ToString
End Function

Public Function Extract() As String
    Dim type As Type = Assembly.LoadFrom("c:\test.dll").GetType("YourNamespace.Test")
    Dim fields As New List(Of FieldInfo)
    Dim field As FieldInfo
    For Each field In type.GetFields
        If field.Name.StartsWith("Prefix_") Then
            fields.Add(field)
        End If
    Next

    fields.Sort(New FieldComparer)

    Dim sb As New StringBuilder
    Dim instance As Object = Activator.CreateInstance(type)
    For Each field In fields
        sb.Append(field.GetValue(instance))
    Next
    Return sb.ToString
End Function

Private Class FieldComparer
    Implements IComparer(Of FieldInfo)

    Public Function Compare(ByVal x As FieldInfo, ByVal y As FieldInfo) As Integer Implements IComparer(Of FieldInfo).Compare
        Return x.Name.CompareTo(y.Name)
    End Function
End Class

Public Class Test
  Public Prefix_15 As String = "501 to 600 bytes"
  Public Prefix_5 As String = "401 to 500 bytes"
  Public Prefix_1 As String = "1 to 100 bytes"
  Public Prefix_2 As String = "101 to 200 bytes"
  Public Prefix_3 As String = "201 to 300 bytes"
  Public Prefix_4 As String = "301 to 400 bytes"
End Class

Public Function GetPrefixString() As String
  Dim type As Type = Assembly.LoadFrom("C:\test.dll").GetType("Test.Test")
  Dim test As Object = Activator.CreateInstance(type)

  Dim fieldList As New List(Of String)
  For Each field As FieldInfo In _
                    From x In type.GetFields _
                    Where x.Name.StartsWith("Prefix_") _
                    Order By Convert.ToInt32(x.Name.Replace("Prefix_", String.Empty))
    fieldList.Add(field.GetValue(test))
  Next

  Return String.Join(String.Empty, fieldList.ToArray)
End Sub