vb.. NET泛型，按名称提取对象成员值

Question

我正在传递2个通用对象和一个字符串到一个函数中，我想找到与字符串匹配的对象的属性并比较它们的值。

下面是一个示例模型:

Public Structure Foo
    Public Bar As String
    Public Nan As String
    Public Tucket As String
End Structure

和调用类:

<TestMethod()> 
Public Sub TestEquality_Class_Pass_Identifier()
    _tester = new GeneralAssert
    Dim expectedFoo = New Foo With {.Bar = "asdf", .Nan = "zxcv", .Tucket = "qwer"}
    Dim actualFoo = New Foo With {.Bar = "qwer", .Nan = "zxcv", .Tucket = "qwer"}
    _tester.TestEquality(expectedFoo, actualFoo, "Bar")
End Sub

将执行业务逻辑的泛型Assert类

Public Class GenericAssert
    Public Sub TestEquality(Of t)(expected As t, actual As t, Optional identifier As String = Nothing)
        Dim expectedType = expected.GetType(), actualType = actual.GetType()
        Assert.AreEqual(expectedType, actualType)
        If (Not identifier Is Nothing) Then
            Dim expectedProperty = expectedType.GetMember(identifier).FirstOrDefault()
            Dim actualProperty = actualType.GetMember(identifier).FirstOrDefault()
            TestEquality(*WhatHere1*, *WhatHere2*)
        End If
    End Sub
End Class

预期结果将是比较expectedFoo ("asdf")和actualFoo ("qwer")的Bar成员。我在FieldInfo, PropertyInfo或MemberInfo中找不到任何值，这将允许我通过名称获得分配给该属性的值。

Answer 1

因为结构的性质和要测试的内容都是已知的，所以我使用FieldInfo对象作为获取字段值的最直接的方法。

Public Sub TestEquality(Of t)(expected As t, actual As t, Optional identifier As String = Nothing)
    Dim expectedType = expected.GetType()
    Dim actualType = actual.GetType()
    Assert.AreEqual(expectedType, actualType)
    If (identifier IsNot Nothing) Then
        Dim expectedField As FieldInfo = expectedType.GetField(identifier, BindingFlags.IgnoreCase Or BindingFlags.Public Or BindingFlags.Instance)
        Dim actualField As FieldInfo = actualType.GetField(identifier, BindingFlags.IgnoreCase Or BindingFlags.Public Or BindingFlags.Instance)
        Assert.AreEqual(expectedField.GetValue(expected), actualField.GetValue(actual))
    End If
End Sub

Answer 2

我不明白为什么在这种情况下不能这样做:

Public Sub AssertEquality(Of T)(ByVal expected As T, ByVal actual As T, identifier As String)
    Dim expected_prop = expected.GetType().GetProperty(identifier, BindingFlags.Instance + BindingFlags.Public)
    Dim actual_prop = actual.GetType().GetProperty(identifier, BindingFlags.Instance + BindingFlags.Public)
    Dim expected_value = expected_prop.GetValue(expected, Nothing)
    Dim actual_value = actual_prop.GetValue(actual, Nothing)
    Assert.AreEqual(expected_value, acutal_value)
End Sub
Sub Main()
    Dim expectedFoo = New Foo With {.Bar = "asdf", .Nan = "zxcv", .Tucket = "qwer"}
    Dim actualFoo = New Foo With {.Bar = "qwer", .Nan = "zxcv", .Tucket = "qwer"}
    AssertEquality(expectedFoo, actualFoo, "Bar")
End Sub