Verify that an object has a certain property

Question

I found C# code for it here

So I tried

Public Function checkProperty(ByVal objectt As Object, ByVal propertyy As String) As Boolean
    Dim type As Type = objectt.GetType
    Return type.GetMethod(propertyy)
End Function

But it throws an error at type.GetMethod(propertyy) saying "Value of type 'System.Reflection.MethodInfo' cannot be converted to 'Boolean'."

What to do?

Answer 1

By splitting the line:

        Return type.GetMethod(propertyy) IsNot Nothing

of dasblinkenlight into the three lines;

        Dim info As System.Reflection.PropertyInfo = type.GetProperty(propertyy)
        Dim reallyExists As Boolean = info IsNot Nothing
        Return reallyExists

the function checkProperty will return true on existing properties.

I cannot comment to the answer of dasblinkenlight, since my reputation is still less than 50, so send my above improvement on his answer as a new answer. I am not happy with this, since it makes the pages on stackoverflow less readable. In order to make this a true answer I include a module I created, in which the lines

Public Function propertyExists( _

through

End Function

are improvements to the code of function checkProperty of natli and dasblinkenlight.

See Verify that an object has a certain property for the question of natli, that I am answering to. See https://stackoverflow.com/posts/9399928/revisions and the question of natli for the answer of dasblinkenlight, that I am commenting to.

By the way: "As you will see below I prefer not to use system namespaces, so that I can directly see what system functions are referenced."

The module with the name net2Module I created to use this follows;

''' <summary>
''' This module with the name net2Module contains
''' tools that need at least .NET Framework 2.0.
''' This module needs System.Reflection.
''' </summary>
Public Module net2Module

''' <summary>
''' If one of the tools fails, the property exceptionMessage will
''' not be nothing, but contain an exception.
''' Each tool will set exceptionMessage to nothing or an exception.
''' </summary>
Public exceptionMessage As System.Exception = Nothing

''' <summary>
''' Checks if a property with some name exist in an object.
''' This function needs System.Reflection.
''' </summary>
''' <param name="objectt">The object.</param>
''' <param name="propertyy">The name of the property.</param>
''' <returns>True if the property exists.</returns>
Public Function propertyExists( _
        objectt As Object, _
        ByVal propertyy As String _
        ) As Boolean
    Try
        exceptionMessage = Nothing
        Dim type As System.Type = objectt.GetType
        Dim info As System.Reflection.PropertyInfo = _
            type.GetProperty(propertyy)
        Dim reallyExists As Boolean = info IsNot Nothing
        Return reallyExists
    Catch ex As System.Exception
        exceptionMessage = ex
        Return False
    End Try
End Function ' propertyExists
End Module ' net2Module

In the following code I succesfully use my function propertyExists in order to close or hide child forms recursively;

Friend Module sharedEnums
Friend Enum objectNamesEnum
    formHandlingClass
    calledForms
    ownedForms
End Enum ' objectNamesEnum

Friend Enum recursiveFormTypesEnum
    calledForms
    ownedForms
End Enum ' recursiveFormTypesEnum

Friend Enum recursiveActionsEnum
    hideForms
    closeForms
End Enum ' recursiveActionsEnum
End Module ' sharedEnums

Friend Class recursiveClass

Friend recursiveFormTypes As New recursiveFormTypesEnum

Friend recursiveActions As New recursiveActionsEnum

Friend Sub hideOrCloseFormsRecursively( _
        formsToHandle As System.Windows.Forms.Form())
    If Not formsToHandle Is Nothing Then
        Dim formToHandle As System.Windows.Forms.Form = Nothing
        Dim propertyToExist As String = String.Empty
        If Me.recursiveFormTypes = recursiveFormTypesEnum.calledForms Then
            propertyToExist = objectNamesEnum.calledForms.ToString
        Else ' Me.recursiveFormTypes = recursiveFormTypesEnum.ownedForms
            propertyToExist = objectNamesEnum.ownedForms.ToString
        End If
        For Each formToHandle In formsToHandle
            Try ' Recurse through the forms to handle
                Dim formObject As Object = formToHandle
                If net2Module.propertyExists(formObject, _
                        objectNamesEnum.formHandlingClass.ToString) Then
                    If net2Module.propertyExists( _
                            formObject.formHandlingClass, propertyToExist) Then
                        If Me.recursiveFormTypes = _
                                recursiveFormTypesEnum.calledForms Then
                            Call Me.hideOrCloseFormsRecursively( _
                                formObject.formHandlingClass.calledForms.ToArray)
                        Else ' Me.recursiveFormTypes = recursiveFormTypesEnum.ownedForms
                            Call Me.hideOrCloseFormsRecursively( _
                                formObject.formHandlingClass.ownedForms)
                        End If
                    End If
                End If
                If net2Module.propertyExists(formObject, propertyToExist) Then
                    If Me.recursiveFormTypes = _
                            recursiveFormTypesEnum.calledForms Then
                        Call Me.hideOrCloseFormsRecursively( _
                            formObject.calledForms.ToArray)
                    Else ' Me.recursiveFormTypes = recursiveFormTypesEnum.ownedForms
                        Call Me.hideOrCloseFormsRecursively( _
                            formObject.ownedForms)
                    End If
                End If
            Catch
            End Try
            Try ' Take the action to take on each found form
                If Me.recursiveActions = _
                        recursiveActionsEnum.hideForms Then
                    Call formToHandle.Hide()
                Else ' Me.recursiveActions = recursiveActionsEnum.closeForms
                    Call formToHandle.Close()
                End If
            Catch
            End Try
        Next
    End If
End Sub ' hideOrCloseFormsRecursively

End Class ' recursiveClass

I would be delighted to read from you if you have been helped by me or not. I am Dutch, so would also like comments on my Engish, so that I can improve it.

Answer 2

First, C# code checks for presence of a method, not a property. Second, C# code compares return to null:

Public Function checkProperty(ByVal objectt As Object, ByVal propertyy As String) As Boolean
    Dim type As Type = objectt.GetType
    Return type.GetProperty(propertyy) IsNot Nothing
End Function

EDIT To check for fields, change the method as follows:

Public Function checkField(ByVal objectt As Object, ByVal fieldName As String) As Boolean
    Dim type As Type = objectt.GetType
    Return type.GetField(fieldName) IsNot Nothing
End Function

Answer 3

You're trying to return type.GetMethod(propertyy), where your example code is returning the result of evaluating if that method is null or not.

try Return type.GetMethod(propertyy) isnot nothing

Answer 4

it is returning the MethodInfo instead and you can just change it as follow:

Public Function checkProperty(ByVal objectt As Object, ByVal propertyy As String) As Boolean
    Dim type As Type = objectt.GetType
    Return type.GetMethod(propertyy) IsNot Nothing
End Function