WinForm ".Show()" method doesn't show up in Visual studio

Question

I am pretty a beginner in using visual studio so I may missed a lot of things. I want to create a custom group in MS Project with a button which I want when I click on it, it would open up a WinForm with some buttons on it. So I created a VSTO project for MS project then added a Ribbon(Visual designer) and a form.

My custom group in Task tab created with a button in it. I double clicked on this button to jump right into it's click handler code, then tried to write a simple code to show my form but it seems it lacks something because intellisense doesn't show up .Show() method and it can not be built. The error I got when I try to build is this:

error BC30469: Reference to a non-shared member requires an object reference.

My form label is Form1 and the simplest code which I wrote in my button click event handler is as follow:

Imports Microsoft.Office.Tools.Ribbon
Imports System.Windows.Forms '(I added this line after the hints)

Public Class Ribbon1
    Private Sub Ribbon1_Load(ByVal sender As System.Object, ByVal e 
        As RibbonUIEventArgs) Handles MyBase.Load
    End Sub

    Private Sub Button1_Click(sender As Object, e As 
    RibbonControlEventArgs) Handles Button1.Click
        Form1.Show() '(The Line which error occurs)
    End Sub
End Class

Answer 1

First of all, you need to check references of your add-in project. By default VSTO add-in projects don't include the System.Windows.Forms assembly reference. If the reference is not there, you need to add it manually. Then in the code you need to use the fully qualified namespace or include it in the beginning of the code file (by using the Imports keyword).