Question Load Assembly Using Reflection

[StoneCodeMonkey]

Hello,

I would like to load a class library at runtime. As such, I thought I could use reflection to do so. However I am receiving the exception "Unable to cast object of type 'MyLibrary.LogSystem' to type 'MainApp.ILog'." in my main application. To start with I created a Class Library (VS2010) with a simple interface and one class that implements the interface.

Public Interface ILog

    Sub Write(ByVal filePath As String, ByVal Fields() As String, ByVal Values() As String)

End Interface

Public Class LogSystem
    Implements ILog

    Public Sub Write(ByVal filePath As String, ByVal Fields() As String, ByVal Values() As String) Implements ILog.Write
        MsgBox("Written")
    End Sub
End Class

Then I created a Winform application and added the exact same interface. In the load event for the form I used reflection to load the assembly file.

Public Class formMain

    Private log As MainApp.ILog
    Private Sub formMain_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        Dim assyPath As String = "C:\My\Visual Studio\Visual Basic\Personal\Runtime Reference\Booya\Booya\bin\Release\MyLibrary.dll"

        Try
            Dim PlugInAssembly As Reflection.Assembly = Reflection.Assembly.LoadFrom(assyPath)
            Dim Types() As Type
            Dim FoundInterface As Type
            Types = PlugInAssembly.GetTypes
            For Each PlugInType As Type In Types
                FoundInterface = PlugInType.GetInterface("MyLibrary.ILog")
                If FoundInterface IsNot Nothing Then
                    log = CType(PlugInAssembly.CreateInstance(PlugInType.FullName), MainApp.ILog)
                    Exit For
                End If
            Next
        Catch ex As Exception
            Debug.Print(ex.Message)
        End Try

    End Sub

End Class

Everthing works up to the point where I try to create an instance:
log = CType(PlugInAssembly.CreateInstance(PlugInType.FullName), MainApp.ILog)

This is where I get the error. Any ideas?

Regards,

 

[JohnH]

Then I created a Winform application and added the exact same interface

I think you mean you defined a new interface with same name and same members in your main app, but that is not the same type as the interface in class lib (MainApp.ILog <> Lib.ILog).
You have to use a common interface type in both assemblies. For example you can have a class lib containing the interface and reference that in both you plugin libraries and your main app.

 

[StoneCodeMonkey]

Brilliant. That worked perfectly.

Thanks