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User999999
User999999

Reputation: 2520

Convert Typed Arrays at runtime

I want to create a Collection based on type declared in 'convertToType' Or 'myElementType'. It has to be a typed collection (which I need for further use). I don't want an Untyped collection.

What I tried so far is

Dim field As PropertyInfo
'_attribute is the name of the property
field = doc.GetType().GetProperty(_attribute)
Dim convertToType As Type = field.PropertyType
Dim myElementType As Type = convertToType.GetElementType()

I've tried:

Dim myList as List(Of convertToType)
Dim myList as List(Of convertToType.GetType())

Different attempts with Arrays. But it's not working. What am I doing wrong here?

Obviously some extra information is in order. My bad :) The method looks like this (i made it somewhat smaller and simplied):

_attribute: Name of the property Me.Value: Is a property inherited from the superclass (refers to a selected value by the user) is an Array[Object]

Public Overridable Overloads Sub GetData(ByRef doc As ClassA)

    Dim fieldOperator As PropertyInfo
    Dim value() As String
    fieldOperator = doc.GetType().GetProperty("operator_" & _attribute)
    fieldOperator.SetValue(doc, Me.[Operator], Nothing)
    If Me.[Operator] <> Proxy.EasyExploreServices.SearchOperator.NoSearch Then
        Dim field As PropertyInfo

        field = doc.GetType().GetProperty(_attribute)
        Dim convertToType As Type = field.PropertyType
        Dim myElementType As Type = convertToType.GetElementType()

        // DO SOME CONVERSION
        Dim arrListObject As ArrayList = New ArrayList()
        For Each myObj As Object In Me.Value
            If (myElementType Is Nothing) Then
                arrListObject.Add(Convert.ChangeType(myObj, convertToType))
            Else
                arrListObject.Add(Convert.ChangeType(myObj, myElementType))
            End If
        Next
        // END CONVERSION

        field.SetValue(doc, // My New Collection //, Nothing)

    End If
End Sub

Problems further on in the code (if no coversion is made). Types other then Strings throw exception because for example Object[] cannot be converted to Int[] (for example)

Upvotes: 2

Views: 88

Answers (1)

Steven Doggart
Steven Doggart

Reputation: 43743

First, you need to get the Type object for the generic List(Of T) class. You can do that like this:

Dim genericType As Type = GetType(List(Of ))

Notice that the type argument is omitted. Next, you need to get the Type object for a List(Of T) where T is whatever type is described by convertToType. To do that, you can use the MakeGenericType method, like this:

Dim specificType As Type = genericType.MakeGenericType({GetType(convertToType)})

Now that you have the Type object, you can create an instance of it. For instance:

Dim myInstance As Object = Activator.CreateInstance(specificType)

It's hard to say where doing this kind of thing would be very useful. Typically, the value of using a generic list is that you get the safety of the added type-checking at compile time. When you are creating it through reflection, and then using it As Object in a late-bound manner, it would seem like you are losing most of it's value.

Upvotes: 2

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