System.NullReferenceException with datagridview - vb.net

Question

I'm trying to fill two arrays with the content of two columns of a Datagridview. I wrote this:
Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
Dim t As Integer = (DataGridView1.Rows.Count - 1)
For i = 0 To t
avx(i) = DataGridView1.Rows(i).Cells("Av").Value
hi(i) = DataGridView1.Rows(i).Cells("h").Value
avsum = Val(avsum + avx(i))
Next
Label2.Text = Val(avsum)
End Sub
When I start debugging, I receive this error at the fourth line of the reported code.
System.NullReferenceException: 'Object reference not set to an instance of an object.'
Does someone know how to solve this issue? How could I initialise Datagridview1? It has been already initialised in Designer section so, if I try to initialise it again, I receive obviously a conflict.

Answer 1

Based on my test, I can not reproduce your problem.
However, I make a sample code that may be similar to your question.
Form_Load event
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim table As New DataTable
table = New DataTable()
table.Columns.Add("Av")
table.Columns.Add("h")
table.Rows.Add("test1", "1001")
table.Rows.Add("test2", "1002")
table.Rows.Add("test3", "1003")
DataGridView1.DataSource = table
DataGridView1.AllowUserToAddRows = False
End Sub
Note: The AllowUserToAddRows property will reduce an extra row.
Button_Click event:
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim t As Integer = (DataGridView1.Rows.Count - 1)
Dim array1(t) As String
Dim array2(t) As String
For i = 0 To t
array1(i) = DataGridView1.Rows(i).Cells("Av").Value
array2(i) = DataGridView1.Rows(i).Cells("h").Value
Next
For index = 0 To t
RichTextBox1.AppendText(array1(index) + Environment.NewLine)
RichTextBox2.AppendText(array2(index) + Environment.NewLine)
Next
End Sub
Final result:

Answer 2

Can you describe about variable avx() and hi()
This error occur maybe datagridview row count greater than Array bound