Can't add column to datagridview programmatically in visual basic.net using method in class

Question

i want to ask something about datagridview in visual basic

i have 1 form name 'form1' and 1 class name 'test' in my project, within the class there is 1 method 'addColumn()'.

i want to add column to datagridview programmatically, when i add directly to form1 from method form1_load, it's success. the code like this

---

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    DataGridView1.Columns.Add("01", 1)

But when i add the column via method from class test,

Dim obj As test

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    obj.addColumns(DataGridView1)
End Sub

i got error this

"Object reference not set to an instance of an object."

code in class test like this

Public Function addColumns(ByVal dgv As DataGridView)
    dgv.Columns.Add("01", 1)
End Function

What wrong with my code?, there are any way to solve this error. Please help me...

Answer 1

You are not declaring a New test object, hence the error.

Dim obj As New test

Or make the function a Shared Function

Public Shared Function addColumns(ByVal dgv As DataGridView)
  dgv.Columns.Add("01", 1)
End Function

Then no need to declare any obj object. Use the function directly.

test.addColumns(DataGridView1)

Answer 2

change Dim obj As test to

Dim obj  as New test

You only declared your obj but not initialized. since obj is null when you call addColumns method you will receive

Object reference not set to an instance of an object.