Question

我不确定如何准确地说出来。我有一个名为BoundedString的类，基本上看起来像：

Public Class BoundedString

    Public Property Value() As String
    Public Property MinLength() As Integer
    Public Property MaxLength() As Integer

End Class

在我的代码的其他地方，我希望能够说：

Public Class SomeClass
    Public Property StringField() As BoundedString(Of 3, 5)
End Class

其中3和5表示MinLength和MaxLength的值。

这样，我可以静态指定有关我的字符串的信息。我发现的最接近的东西似乎是泛型或属性，但我不认为泛型让你指定具体的价值观。是否有人知道这样做的语言功能？

Answer 1

您可能需要重新定义New()方法：

Public Class BoundedString

    Public Property Value As String
    Public Property MinLength As Integer
    Public Property MaxLength As Integer

    Public Sub New(myMinLength As Integer, myMaxLength As Integer)
        MinLength = myMinLength
        MaxLength = myMaxLength
    End Sub

End Class

Public Class SomeClass

    Dim _StringField As BoundedString
    Public Property StringField As BoundedString
        Get
            Return _StringField
        End Get
        Set(value As BoundedString)
            If value.MinLength = 3 AndAlso value.MaxLength = 5 Then
                _StringField = value
            End If
        End Set
    End Property

End Class

Answer 2

以下是我如何使用属性完成此操作。代码的工作原理是：

定义一组属性，MinLengthAttribute和MaxLengthAttribute，可用于字段或属性。
定义一个方法GetPropertyAttribute，该方法从对象的属性中检索属性。
在构建GetPropertyAttribute时使用BoundedString检索GetPropertyAttribute的最小和最大长度。

这允许您将长度直接关联到属性旁边，这使得类定义相当容易阅读。不可否认，必须使用<AttributeUsage(AttributeTargets.Field Or AttributeTargets.Property)> Public Class MinLengthAttribute : Inherits Attribute Public Property MinLength As Integer ''' <param name="minimumLength">The minimum length of this field/property.</param> Public Sub New(ByVal minimumLength As Integer) minimumLength = minimumLength End Sub End Class <AttributeUsage(AttributeTargets.Field Or AttributeTargets.Property)> Public Class MaxLengthAttribute : Inherits Attribute Public Property MaxLength As Integer ''' <param name="maximumLength">The maximum length of this field/property.</param> Public Sub New(ByVal maximumLength As Integer) MaxLength = maximumLength End Sub End Class ''' <summary> ''' Gets the attribute TAttribute of the property <paramref name="strPropertyName" /> on this class. ''' </summary> ''' <typeparam name="TAttribute">The type of the attribute to retrieve.</typeparam> ''' <param name="oObj">An object that has a property named <paramref name="strPropertyName"/>.</param> ''' <param name="strPropertyName">The property to get an attribute from.</param> ''' <remarks> ''' Requires that <paramref name="strPropertyName"/> has only one attribute ''' of type TAttribute. Throws an exception if this is not the case. ''' </remarks> <Extension> Public Function GetPropertyAttribute(Of TAttribute As Attribute)(oObj As Object, ByVal strPropertyName As String) As TAttribute Dim piPropertyInfo As PropertyInfo = oObj.GetType().GetProperty(strPropertyName) Dim aobjAttributes As Object() = piPropertyInfo.GetCustomAttributes(True) Dim lstAttributes As List(Of TAttribute) = (From objAttribute As Attribute In aobjAttributes.OfType(Of TAttribute)() Select CType(objAttribute, TAttribute)).ToList() If lstAttributes.Count = 1 Then Return lstAttributes(0) Else Throw New InvalidOperationException("Property " & strPropertyName & " has " & lstAttributes.Count & " attributes of provided type. GetPropertyAttribute requires that" & strPropertyName & " only has one property of the provided type.") End If End Function Public Class SomeClass <MinLength(0)> <MaxLength(30)> Public Property String1 As BoundedString <MinLength(5)> <MaxLength(10)> Public Property String2 As BoundedString <MinLength(0)> <MaxLength(100)> Public Property String3 As BoundedString Public Sub New(ByVal string1 As String, ByVal string2 As String, ByVal string3 As String) String1 = New BoundedString(string1, GetPropertyAttribute(Of MinLengthAttribute)("String1").MinLength, GetPropertyAttribute(Of MaxLengthAttribute)("String1").MaxLength) String2 = New BoundedString(string1, GetPropertyAttribute(Of MinLengthAttribute)("String2").MinLength, GetPropertyAttribute(Of MaxLengthAttribute)("String2").MaxLength) String3 = New BoundedString(string1, GetPropertyAttribute(Of MinLengthAttribute)("String3").MinLength, GetPropertyAttribute(Of MaxLengthAttribute)("String3").MaxLength) End Sub End Class来检索最小/最大长度值有点不稳定。

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是否可以在编译时将具体值与字段相关联？

2 个答案: