如何使用属性本身获取属性的名称

Question

I've run into an issue where I need to get the name of a property for logging purposes. I'm sure there is a way to do this in VB.Net using some amalgam of reflection and lambda expressions, but I've been unsuccessful so far.

What I'm trying to do is convert this:

objAddress.AddressLine

to this:

"AddressLine"

Answer 1

In the past, I've used a method I found online for doing this with INotifyPropertyChanged . I can't remember exactly where, but this details the same resolution:

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

The main benefit of doing this is refactoring. If I ever rename my property, the Lambda (and by extension NotifyPropertyChanged event) changes automatically.

---

Update (2015)

It may be worth mentioning that the new features in Visual Studio 2015 make this even easier. Below is the same code shown above, but using the new nameof feature (Details of this, and of other new features can be found Here ).

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

You can even use nameof on the subscriber side, in order to determine if the property is the one you care about:

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

Answer 2

For someone who is still looking for an elegant solution, in the latest version of VB and C# you can use "nameof()".

C#:

var propertyName = nameof(objAddress.AddressLine)

VB .NET:

Dim propertyName = nameof(objAddress.AddressLine)

Note that if you do not have an instance of an object you can just use it's class name.

Answer 3

This will show the current Method. You may want to replace the "get_" prefix of the property name.

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

From 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

I decided to go with the_lotus's response to my initial question which was to use a constant. If I find a more dynamic way to do this in the near future I'll try to post it. lotus, if you happen to see this an answer the question with your comment, i'll switch the answered status over to you.

Answer 6

Using the System.Runtime.CompilerServices works wonders in this case, as of Net4.5. [See Caller Information ] The optional CallerMemberName string can be used to identify what method/property called the log.

From 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

---

Different implementation showing results from a Property Call

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>