How do you access form variable from a module in vb.net

First, the variable should be declared public (to access from the same of different assembly) or internal (to access from the same assembly, so it should be used more often). This "variable" is actually should be a member, either a field or a property. Usually, proper encapsulation requires it to be a property, not a field. Having any fields accessible from outside is considered a bad coding style.

If the member is static, you access it from outside as MyModule.MyMember. If this is an instance member (non-static), you need to have an instance of the module (via a constructor you call somewhere which returns you the reference to the instance), and access it as MyInstance.MyMember.

—SA

You cannot directly access a class without a reference to an instance of that class. Your best bet might be something like this:

Module Module1
    Private m_MyForm As Form1
    Public ReadOnly Property MyForm() As Form1
        Get
            If IsNothing(m_MyForm) Then m_MyForm = New Form1
            Return m_MyForm
        End Get
    End Property
    Public Sub WriteLog(ByVal txt As String)
        MyForm.TextBox3.Text += txt + vbNewLine
    End Sub
End Module

Now anywhere in your application you can access Form1 using Module1.MyForm.

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