Instantiate a class by its type name??

[MerrionComputin]

OK - I have a plug in framework where my application can have 3rd party plug-ins added via the .config file (provided they confrom to the IPlugIn interface...)

What I have so far reads the Type Name and checks if it supports the interface OK - but how do I instantiate an object of that type if it does?

I have.....
App.config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
   <configSections>
      <!-- Extra custom configuration sections -->
      <section name="printerEventListeners" 
type="PrinterMonitorService.CustomConfigurationSectionReaders.PrinterEventListenersSectionReader" />
     
   </configSections>
    
    <printerEventListeners>
       <!-- Key = the unique name by which the listener is known,
            ClassType = the full type name of the class implementing IPrinterEventListenerBase ,
            CommandLine = startup parameters for that class -->
       <printerEventListener key="printerEventListener1" 
           classType="PrinterMonitorService.PrinterMonitorLogfileListener"
           commandLine="c:\printerEventListener1.log" />
    </printerEventListeners>

Then in the application....

For Each PrintJobListener In PrintJobListeners
                If PrintJobListener.ImplementingClassType.IsSubclassOf(GetType(PrintJobMonitorListenerBase)) Then
                    '\\ Add an instance of the PrintJobMonitorListenerBase derived class...
                    If ApplicationTracing.TraceVerbose Then
                        Trace.WriteLine("PrintJobMonitorListenerBase derived class: " & PrintJobListener.ImplementingClassType.ToString, Me.GetType.ToString)
                        '<-- What to put here ????
                    End If
                End If
            Next

Thanks in advance,
Duncan

[nemaroller]

Well, im going to need some code like that shortly, so Im sure if you dont have an answer by then, I will be helping..

[Edneeis]

You can use Activator.CreateInstance if you have the full namespace or 'type' of the object you can also use reflection via the Assembly.LoadFrom method. You can also load a type via a string using Type.GetType("MyNamespace.ObjectTypeName") Sorry for such a brief post but I'm headed out the door.

[PeteD]

yep... something like this:

Imports System.Reflection
 
'Then use
 
      Dim a As [Assembly] = [Assembly].Load("YourDllProject")
 
      T = a.GetType("YourDllProject.MainForm", True)
 
      'Create an instance of the form
      Dim o As Object = Activator.CreateInstance(t)
 
      'Show the form
     Dim mainForm As Form = CType(o, Form)
     mainForm.Show()

[nemaroller]

Ok... So if I have a tabpageclass named "AdditionalInfo", this should work (but it doesn't)

Dim o As Object =  Activator.CreateInstanceFrom("ReportExecHelper.AdditionalInformationTabPageClass.vb", "TabPage")
 myTabPage = CType(o, TabPage)

This is the error I get:

An unhandled exception of type 'System.IO.FileNotFoundException' occurred in mscorlib.dll

Additional information: File or assembly name ReportExecHelper.AdditionalInformationTabPageClass, or one of its dependencies, was not found.

So I switched the original line with this ..

Dim o As Object = Activator.CreateInstanceFrom("ReportExecHelper.dll", "AdditionalInformationTabPageClass")

And got this...

An unhandled exception of type 'System.TypeLoadException' occurred in mscorlib.dll

Additional information: Could not load type AdditionalInformationTabPageClass from assembly ReportExecHelper, Version=1.0.1370.15851, Culture=neutral, PublicKeyToken=null.

So what gives? All i want to do is create an instance of the object using its Name ... i.e. CreateInstance("MyForm1")

[Edneeis]

You have to use the full namespace of the object:

Dim o As Object = Activator.CreateInstanceFrom("ReportExecHelper.dll", "RootOrOtherNamespaceHere.ObjectName")

I think you also might need to use the full path of the assembly.

[nemaroller]

Yea... I don't know,I can't get it to work.

Does this only work with class libraries? (.dll's)?

So if I made a test project with two forms, I couldn't possibly call the second form using .CreateInstanceFrom("Form2")

[Edneeis]

Actually I pulled some old code where I used this and if you use CreateInstanceFrom or CreateInstance with the assemblyname parameter then it returns an ObjectHandle which can be used in remoting (and maybe other ways too) instead of the actual object. If you were to use that you'd have to unwrap it as the type that it is, but like I said I don't know if that is specific to remoting or not. If you just want to dynamically load something try this:

'load assembly via the path
        Dim asm As Reflection.Assembly = Reflection.Assembly.LoadFrom("E:\Code\NET\Practice\TestBed6\bin\TestBed6.exe")
        'load the type from the assembly via the full namespace
        Dim obj As Object = Activator.CreateInstance(asm.GetType("TestBed6.Form5"))
        DirectCast(obj, Form).ShowDialog()

And no it doesn't have to be a dll.

[nemaroller]

I got it to work finally.

Dim ty As Type = Type.GetType("ReportExecHelper.AdditionalInformationTabPageClass")
            myobj = Activator.CreateInstance(ty)
            TabControl1.TabPages.Add(CType(myobj, TabPage))