CODEWITHSUNDEEP
vb.netsystem.reflection
MattCucco
MattCucco

Reputation: 133

Using GetValue and System.Reflection

Using VB.Net. I'm trying to get the property values from two objects of the same class and compare them. If the values are different then i want to add them to a string showing what the values were and what they changed to. I'm having problems with the GetValue. Here is the code for this function:

  Public Function GetRowChangesList(ByVal Before As IEnumerable(Of Object), ByVal After As IEnumerable(Of Object), ByRef isNew As Boolean) As String

    Dim TheseChanges As List(Of String) = Nothing

    'any errors, return ""
    Try

        'If Lists are both empty, return
        If Before Is Nothing And After Is Nothing Then
            Return ""
        End If

        'Figure out the object type and make sure before and after match
        Dim DataTypeBefore As Type
        Dim DataTypeAfter As Type

        DataTypeBefore = Before.Single.GetType()
        DataTypeAfter = After.Single.GetType()

        'if they don't match function won't work
        If DataTypeBefore IsNot DataTypeAfter Then
            Return ""
        End If


        Dim myField As PropertyInfo() = Before.Single.GetType().GetProperties()
        Dim myField2 As PropertyInfo() = After.Single.GetType().GetProperties()

        'Find the changes
        Dim index As Integer

        For index = 0 To myField2.Length - 1
            If Not myField(index).GetValue(Before) = myField2(index).GetValue(After) Then

                TheseChanges(0) += ("Change happened at:  " + myField(index).Name.ToString + "  Values changed from: " +
                     myField(index).GetValue(Before).ToString + " To " + myField2(index).GetValue(After).ToString)

            End If
        Next

    Catch ex As Exception

        'send error
        SendErrorEmail(ex, "Saving changes for: '" + Before.Single.GetType().ToString)

    End Try

    'return
    Return TheseChanges(0)

End Function

There should only be one thing that changed if anything changes at all. That's why it just returns the first element. When I'm debugging it catches an exception every time. The errors it gives me are as follows:

        If Not myField(index).GetValue(Before) = myField2(index).GetValue(After) Then   error BC30199: '(' expected.    
    TheseChanges(0) = ("Change happened at:  " + myField(index).Name.ToString + "  Values changed from: " + error BC30201: Expression expected. 
    myField(index).GetValue(Before).ToString + " To " + myField2(index).GetValue(After).ToString)   error BC37237: ')' is not a valid format specifier  
    End If  error BC30201: Expression expected. 
    Next    error BC30201: Expression expected.

EDIT: I just tried this method and still got the same errors(Code Below). Also just tried changing '=' to isNot (didn't change anything) and I also just tried adding parens around each value and that also didn't change anything. 

If myField(index).GetValue(myField(index).Name) = myField2(index).GetValue(myField(index).Name)

Upvotes: 2

Views: 938

Answers (1)

dummy
dummy

Reputation: 4284

Change:

If Not myField(index).GetValue(Before) = myField2(index).GetValue(After) Then

To:

If Not myField(index).GetValue(Before.Single) = myField2(index).GetValue(After.Single) Then

Explanation:

myField is created for the Type Before.Single, but you are using it with Before which is not the same type as Before.Single.

Upvotes: 1

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