vb.net - 如何使用属性本身获取属性的名称

Question

我遇到了一个问题，我需要获取属性的名称以进行日志记录。我确信有一种方法可以在 VB.Net 中使用一些反射和 lambda 表达式的混合体来做到这一点，但到目前为止我还没有成功。

我想要做的是转换这个：

objAddress.AddressLine

对此：

"AddressLine"

Answer 1

过去，我使用我在网上找到的一种方法来执行此操作INotifyPropertyChanged。我不记得确切的位置，但这详细说明了相同的分辨率：

http://paulstovell.com/blog/strong-property-names

C＃

public class Test : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private string _Name;

    public string Name
    {
        get { return _Name; }
        set
        {
            _Name = value;
            RaisePropertyChanged(() => Name);
        }
    }

    private void RaisePropertyChanged(Expression<Func<object>> property)
    {
        MemberExpression exp = property.Body as MemberExpression;

        if (exp != null)
        {
                PropertyChanged(this, new PropertyChangedEventArgs(exp.Member.Name));
        }
    }


}

VB

Public Class Test
    Implements INotifyPropertyChanged

    Public Event PropertyChanged(sender As Object, e As PropertyChangedEventArgs) Implements INotifyPropertyChanged.PropertyChanged
    Private _Name As String

    Public Property Name() As String
        Get
            Return _Name
        End Get
        Set(value As String)
            _Name = value
            RaisePropertyChanged(Function() Me.Name)
        End Set
    End Property

    Private Sub RaisePropertyChanged(Of T)(propertyName As Expression(Of Func(Of T)))
        Dim exp As MemberExpression = TryCast(propertyName.Body, MemberExpression)

        If exp IsNot Nothing Then
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(exp.Member.Name))
        End If
    End Sub



End Class

这样做的主要好处是重构。如果我重命名我的属性，Lambda（以及扩展的 NotifyPropertyChanged 事件）会自动更改。

---

更新 (2015)

值得一提的是，Visual Studio 2015 中的新功能使这变得更加容易。下面是上面显示的相同代码，但使用了新nameof功能（可以在此处找到有关此功能和其他新功能的详细信息）。

C＃

public class Test : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    string _Name;

    public string Name
    {
        get { return _Name; }
        set
        {
            _Name = value;
            RaisePropertyChanged(nameof(Name));
        }
    }

    private void RaisePropertyChanged(string property)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(property));
        }
    }
}

VB

Public Class Test
    Implements INotifyPropertyChanged

    Public Event PropertyChanged(sender As Object, e As PropertyChangedEventArgs) Implements INotifyPropertyChanged.PropertyChanged
    Private _Name As String

    Public Property Name() As String
        Get
            Return _Name
        End Get
        Set(value As String)
            _Name = value
            RaisePropertyChanged(NameOf(Name))
        End Set
    End Property

    Private Sub RaisePropertyChanged(propertyName As String)
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
    End Sub

End Class

您甚至可以nameof在订阅者端使用，以确定该属性是否是您关心的属性：

    private static void PropChanged(object sender, PropertyChangedEventArgs e)
    {
        if (e.PropertyName == nameof(Test.Name))
        {
            Console.WriteLine("The Property I care about changed");
        }
    }

Answer 2

对于仍在寻找优雅解决方案的人，在最新版本的 VB 和 C# 中，您可以使用“nameof()”。

C＃：

var propertyName = nameof(objAddress.AddressLine)

VB.NET：

Dim propertyName = nameof(objAddress.AddressLine)

请注意，如果您没有对象的实例，则可以只使用它的类名。

Answer 3

这将显示当前的方法。您可能想要替换属性名称的“get_”前缀。

Public Class People
    Public Shared ReadOnly Property Address As String
        Get
            Return System.Reflection.MethodInfo.GetCurrentMethod().ToString()
        End Get
    End Property
End Class

' print it
System.Diagnostics.Debug.Print(People.Address)

Answer 4

来自MSDN

Imports System
Imports System.Reflection
Class MyClass1
    Private myProperty1 As Integer 
    ' Declare MyProperty. 

    Public Property MyProperty() As Integer 
        Get 
            Return myProperty1
        End Get 
        Set(ByVal Value As Integer)
            myProperty1 = Value
        End Set 
    End Property 
End Class 'MyClass1

Public Class MyTypeClass
    Public Shared Sub Main(ByVal args() As String)
        Try 
            ' Get Type Object corresponding to MyClass. 
            Dim myType As Type = GetType(MyClass1)
            ' Get PropertyInfo object by passing property name. 
            Dim myPropInfo As PropertyInfo = myType.GetProperty("MyProperty")
            ' Display Name propety to console.
            Console.WriteLine("The {0} property exists in MyClass.", myPropInfo.Name)
        Catch e As NullReferenceException
            Console.WriteLine("The property does not exist in MyClass.", e.Message.ToString())
        End Try 
    End Sub 'Main
End Class 'MyTypeClass 

Answer 5

我决定使用 the_lotus 对我最初的问题的回答，即使用常量。如果我在不久的将来找到一种更动态的方式来做到这一点，我会尝试发布它。莲花，如果你碰巧看到这是一个用你的评论回答问题的问题，我会将已回答的状态切换给你。

Answer 6

在这种情况下，使用 System.Runtime.CompilerServices 可以创造奇迹，从 Net4.5 开始。[参见调用者信息] 可选的 CallerMemberName 字符串可用于标识调用日志的方法/属性。

来自MSDN

Private Sub DoProcessing()  
    TraceMessage("Something happened.")  
End Sub  

Public Sub TraceMessage(message As String,  
        <System.Runtime.CompilerServices.CallerMemberName> Optional memberName As String = Nothing,  
        <System.Runtime.CompilerServices.CallerFilePath> Optional sourcefilePath As String = Nothing,  
        <System.Runtime.CompilerServices.CallerLineNumber()> Optional sourceLineNumber As Integer = 0)  

    System.Diagnostics.Trace.WriteLine("message: " & message)  
    System.Diagnostics.Trace.WriteLine("member name: " & memberName)  
    System.Diagnostics.Trace.WriteLine("source file path: " & sourcefilePath)  
    System.Diagnostics.Trace.WriteLine("source line number: " & sourceLineNumber)  
End Sub  

' Sample output:  
'   message: Something happened.  
'   member name: DoProcessing  
'   source file path: C:\Users\username\Documents\Visual Studio 2012\Projects\CallerInfoVB\CallerInfoVB\Form1.vb  
'   source line number: 15

---

显示属性调用结果的不同实现

Class Foo
    Public ReadOnly Property ThisPropertyObject As Object
        Get
            LogManager.Ping
            Return Nothing
        End Get
    End Property
    Sub New()
      Dim this = ThisPropertyObject 
    End Sub
End Class

Public Module LogManager
        Public Sub Ping(<CallerMemberName> Optional memberName As String = Nothing,
                        <CallerFilePath> Optional sourcefilePath As String = Nothing,
                        <CallerLineNumber> Optional sourceLineNumber As Integer = 0)
            Trace.Writeline(String.Format("[{0}]|{1}|LN:{2}] <PING>",
                                          Path.GetFileName(sourcefilePath),
                                          memberName,
                                          sourceLineNumber)
                                          )
                            )
        End Sub

End Module

'! Results from 'DebugView'
' [20692][LogTestFile.vb|ThisPropertyObject|LN:62] <PING>