Solved

vb.net how to instantiate a class based on a variable name at runtime

Posted on 2011-02-25
6
467 Views
Last Modified: 2012-05-11
I'm sure this is easy, but my search is coming up short.   I want to be able to instantiate an object (in this case a Prompt Screen), but the Class name is variable based on what the user is doing.  

This is the statement:
    myPromptScreen = New [VariableClassName]

Thanks in advance.
0
Comment
Question by:jackiemeck
6 Comments
 
LVL 85

Expert Comment

by:Mike Tomlinson
ID: 34984591
0
 
LVL 9

Expert Comment

by:rawinnlnx9
ID: 34984603
Look at the 5th option down. Regardless though one of these will work for you. It's the right way:

http://msdn.microsoft.com/en-us/library/system.activator.createinstance.aspx
0
 
LVL 41

Expert Comment

by:graye
ID: 34989711
Here is a small chunk of code that I've used to allow a program to dynamically load a "plug-in" at run time.  It uses the techniques as described above

Imports System.IO
Imports System.Reflection

Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim DLL_File As String

        ' fill the combobox with the list of available plug-in DLLs
        For Each DLL_File In Directory.GetFiles(Application.StartupPath & "\" & My.Settings.PluginDirectory, "Plug*.dll")
            ComboBox1.Items.Add(DLL_File)
        Next

        ' make a default item
        If ComboBox1.Items.Count > 0 Then
            ComboBox1.Text = ComboBox1.Items(0).ToString
        End If
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim Assmbly As Reflection.Assembly
        Dim PlugInType As Type
        Dim pi As PluginBase

        ' load the DLL file using the "signature" of the base class
        Assmbly = Reflection.Assembly.LoadFrom(ComboBox1.Text)

        PlugInType = Assmbly.GetType(Assmbly.GetName.Name & "." & Assmbly.GetName.Name, True, True)
        pi = CType(Activator.CreateInstance(PlugInType), PluginBase)

        ' execute a method on the plug in
        pi.DoSomething()
    End Sub
End Class

Open in new window

0
Active Directory Webinar

We all know we need to protect and secure our privileges, but where to start? Join Experts Exchange and ManageEngine on Tuesday, April 11, 2017 10:00 AM PDT to learn how to track and secure privileged users in Active Directory.

 

Author Comment

by:jackiemeck
ID: 35826224
I have searched numerous resources and have found a lack of detailed examples along the lines of what I'm trying to do.  I know I need "CreateInstance", but I don't know how to format it.  I'll restate by issue with hopefully a little better detail:

I have 15 Forms that each include the same methods.  I don't know which of the Forms the user will decide to activate until runtime.  Basically, there is a loop of 1 through 15, and if the Form is selected, we need to run the identical method inside it.

' The assembly is called "MyProgram", but I'm not sure where that goes.

FormName(1)   = "FormForReportA"
FormName(2)   = "FormForReportB"
FormName(...)   = (etc)
FormName(15)   = "FormForReportZ"

for x = 1 to 15
    myPromptScreen(x) = CreateInstance("NotSureWhatGoesHere", FormName(x))
next x

For x = 1 to 15
    if UserSelected(x) = true then
        myPromptScreen(x).InitializeData()
        myPromptScreen(x).CalculateData()
    end if
next x

Thanks in advance...
0
 
LVL 85

Accepted Solution

by:
Mike Tomlinson earned 500 total points
ID: 35826833
Try something like this:

    Dim asm As System.Reflection.Assembly = System.Reflection.Assembly.GetExecutingAssembly
    ...
    for x = 1 to 15
        myPromptScreen(x) = asm.CreateInstance(asm.GetName.Name & "." & FormName(x))
    next x
0
 

Author Closing Comment

by:jackiemeck
ID: 35833514
That's perfect!  It's exactly what I needed.  Thanks so much.
0

Featured Post

Free Tool: Subnet Calculator

The subnet calculator helps you design networks by taking an IP address and network mask and returning information such as network, broadcast address, and host range.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Well, all of us have seen the multiple EXCEL.EXE's in task manager that won't die even if you call the .close, .dispose methods. Try this method to kill any excels in memory. You can copy the kill function to create a check function and replace the …
Since .Net 2.0, Visual Basic has made it easy to create a splash screen and set it via the "Splash Screen" drop down in the Project Properties.  A splash screen set in this manner is automatically created, displayed and closed by the framework itsel…
Two types of users will appreciate AOMEI Backupper Pro: 1 - Those with PCIe drives (and haven't found cloning software that works on them). 2 - Those who want a fast clone of their boot drive (no re-boots needed) and it can clone your drive wh…
A short tutorial showing how to set up an email signature in Outlook on the Web (previously known as OWA). For free email signatures designs, visit https://www.mail-signatures.com/articles/signature-templates/?sts=6651 If you want to manage em…

821 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question