[Washi]

Plug-in System in VB.NET

Hello all,

Today i'm going to show a way to create a basic plugin system with interfaces. I hope i'm clear enough and don't go to fast. I've split up the
tutorial into 6 steps.

• Designing the Main Application
  


• The Connector Library
  


• The Connector in the Main Application
  


• Creating the Plug-in
  


• Finishing the source
  


• Test!
  

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Step 1 - Designing the Main Application

To start, you have to create first a new project that will represent your main application.

Spoiler (Click to View)
[img]http://imageshack.us/a/img839/1107/pic1mr.png[/img]


Then design the form something like this:

[img]http://imageshack.us/a/img560/6015/pic2ez.png[/img]

The first button is to load the user created plugin file, and the second to run it. I've created a groupbox with two labels in it to show you what the output can be. In this example we will change those label's texts by using the plug-in assembly.

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Step 2 - The Connector Library

After the designing of your main application, save it and open a new visual studio window and create another project. This will be a class library that will connect the plugin with the main application.

Spoiler (Click to View)
[img]http://imageshack.us/a/img43/3347/pic3au.png[/img]


Delete the contents of the standard class file and create two interfaces.

[img]http://imageshack.us/a/img685/1561/pic4o.png[/img]

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What is an interface?
(skip this if you know what it is) Spoiler (Click to View)
An interface is a class with functions or subs that don't have any body. If you implement an interface to a class, the class must have those functions or subs in it. In fact you can say that an interface describes a class. You can compare it with a car and a truck, they are both vehicles. So the interface can be something like this:

Code

Public Interface Vehicle
  Sub Forwards()
  Sub Backwards()
  Sub TurnLeft()
  Sub TurnRight()
End Interface

If you implement it into the class Car, then that class must have those four subs, forwards, backwards, turnleft and turnright. And for the Truck it's the same story.

For example:

Code

Public Class Car
    Implements Vehicle

    Public Sub Backwards() Implements Vehicle.Backwards
  'Do stuff to move car backwards
    End Sub

    Public Sub Forwards() Implements Vehicle.Forwards
  'Do stuff to move car Forwards
    End Sub

    Public Sub TurnLeft() Implements Vehicle.TurnLeft
  '...
    End Sub

    Public Sub TurnRight() Implements Vehicle.TurnRight
  '...
    End Sub
End Class

Public Class Truck
    Implements Vehicle

    Public Sub Backwards() Implements Vehicle.Backwards
  'Do stuff to move truck backwards
    End Sub

    (...)

End Class

But why is it useful?
Well now you can access both vehicles into one variable. For example, if the user has the choice to choose a vehicle, you can store the vehicle into a Vehicle variable and start one of the subs. If you don't use an interface, and you have a lot types of vehicles, you have to write a lot of code to process all the vehicles.

An example below to make it clear:

Code

Module Example

    Public Sub Main()

        'ask first the user what kind of vehicle he wants
  Console.WriteLine("Choose option 1 (car) or 2 (truck)")

        'get the vehicle
  Dim int As Integer = CInt(Console.ReadLine())

        'declare a new vehicle
  Dim vehicle As Vehicle

        'check if input is 1 or 2.
  If int = 1 Then
    vehicle = New Car()
  Else
    vehicle = New Truck()
  End If

        'run some subs of the vehicle.
  vehicle.Forwards()
  vehicle.TurnLeft()

    End Sub

End Module

[/code]

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The IPlugin and IConnector interfaces will be used in the main application and the plug-in assembly.

• The IPlugin will be like the Entrypoint (Start) of the class. That's why this interface contains the sub StartPlugIn.
  


• The IConnector will be the connector that connects the Main App with the Plug-in. The first two functions will get the labels' texts, and the next two subs will set the labels' texts. The last sub will disconnect the plug-in from the main application.
  

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Step 3 - The Connector in the Main Application

After creating the connector library, save and build it and go back to your main application. Add your Plugin connector library reference to the project and create a new class, called Connector. Then add the following code to implement the IConnector interface.

Code

Imports PluginConnector

Public Class Connector
    Implements IConnector

If you press enter, the functions/subs Disconnect, GetLabel1Text, GetLabel2Text, SetLabel1Text and SetLabel2Text will be automatically added to your class. Before we add the code of the bodies of the functions and subs, we need to make another sub called Public Sub New(frm as Form1) and another variable. This is to specify the Form you want to edit the labels' texts. You'll get something like this:

Code

Dim frm As Form1

    Public Sub New(ByVal frm As Form1)
  Me.frm = frm
    End Sub

Now we can write the code for the four label functions and subs. Just use Return frm.Label.Text for the get functions and frm.Label.Text = ... for the set subs. We'll write the disconnect sub later.

After this, your source will look something like this picture below.

[img]http://imageshack.us/a/img10/3696/pic8fm.png[/img]

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Step 4 - Creating the Plug-In

Save the main application project and open another visual studio window, and create another class library. This will be the plug-in assembly itself.

Spoiler (Click to View)
[img]http://imageshack.us/a/img853/6502/pic9ld.png[/img]


First of all, add the plugin connector library reference to your project . Then add a form and design it to something like this:

[img]http://imageshack.us/a/img837/4160/pic11x.png[/img]

The first button will run the Get functions to get the labels' texts and put them into the textboxes. The Set button will run the Set Functions to set the labels' texts to the textboxes texts.

Back to your first class. Rename it to StartOfPlugin and implement the IPlugin interface. The sub StartPlugIn will be automatically added. In this sub we will create a new form1 and show it.

Code

Dim frm As New Form1
  frm.Connector = connector
  frm.Show()

As you maybe see, the frm.Connector doesn't exist. That's why we have to add the following line at the top of the form's class.

Code

Public Connector As IConnector

Now double click onto the buttons and fill the subs with code. One to get and one to set. Then add a formclosing event to disconnect from the main application when the form closes.

After this, you have something like this:

[img]http://imageshack.us/a/img198/3456/pic12aj.png[/img]

Save the application and go back to the main application.

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Step 5 -Finishing the source

At the very top of the main application form's source add the following line.

Code

Imports System.Reflection

Then add a new variable inside the class. This will represents the current running plug-in.

Code

Public CurrentPlugIn As IPlugin

Now double click onto button1 and use the following code to let the user open a file and set the CurrentPlugIn with the selected file.

Code

Dim ofd As New OpenFileDialog
  If ofd.ShowDialog = Windows.Forms.DialogResult.OK Then

    'load the assembly
    Dim pluginassembly As Assembly = Assembly.LoadFile(ofd.FileName)

    'get the StartOfPlugin class by using GetType("<typename>")
    Dim pluginclass As IPlugin = CType(Activator.CreateInstance(pluginassembly.GetType(pluginassembly.GetName.Name & ".StartOfPlugin")), IPlugin)

    'sets the loaded plugin to the current plugin
    CurrentPlugIn = pluginclass

  End If

Then double click onto button2 and add the following line to start the plugin.

Code

CurrentPlugIn.StartPlugIn(Connector)

Your form code will now look something like this:

[img]http://imageshack.us/a/img713/3707/pic13c.png[/img]

Go back to the Connector class and write the following line into the Disconnect sub to clean the CurrentPlugIn Variable.

Code

frm.CurrentPlugIn = Nothing

Now you're done with the source.

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Step 6 - Test!

If you did everything right, you'll get something like this gif animation:

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I hope you enjoyed this tutorial. Feel free to give comments. Please if you use this tutorial, say post a thanks 😉

If you want to download the project, click here

For the ones who don't trust the file. I dont really understand why there are 2 false positives since its a rar archive with sources.
VirusTotal scan

That's all 😉

[Ethernal Five]

Looks like a very good tutorial, very detailed and explaned alot. Thanks ;)

[MoBaT]

This is such a well built tutorial. I will be sure to use this.

[ibloodqman]

Greatest tutorial i ever seen (honestly). Big Vouch, i'd rep you but i can't.. keep it up

[Androcir]

Very nice tutorial mate, you made it very compreensive (if that's how it is spelled... I don't know..)

Anyways.. ;)

[Washi]

I'm glad you all liked it 😉
Thanks for the commentary.

[nuk]

Very nice indeed. Great share man! Def. a keeper on the tutorials :)

[M0D3M]

Excellent tutorial. This is the first tutorial I have seen on this subject. However I have not been on in awhile. One green apple for you.

[nrd]

this was a great tutorial, can come in handy for some programs in the future

[The MammoTh]

This one is better then I coded, do you mind if I use it?

[ParkII]

Yeah...I needed this a long time ago ...

[Sixem]

That's pretty damn cool, detailed and easy to understand, great job.

[Washi]

This one is better then I coded, do you mind if I use it?

Of course you 're allowed, this is a tutorial, and you may use the source. 😉

Yeah...I needed this a long time ago ...

That's pretty damn cool, detailed and easy to understand, great job.

I'm glad you two liked it 😁

[log dot zip]

Yip yippity kiyay! (Didn't get the reference? Oh well) Anyways: AWESOME JOB.

[Kōtei]

Needs more publicity, truly a grand guide.