Asp.net - Add Custom Column Using Loop In Aspxgridview (VB)?

how to add custom column to aspxgridview column using looping to get name and value of column.

here is my code behind :

Protected Sub gridSubmission_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles gridSubmission.Init
Dim colBaru As GridViewDataTextColumn = New GridViewDataTextColumn()
For i As Integer = 1 To 6

[code]....

which i used to add new column at aspxgridview.but its getting an error, "An item with the same key has already been added."second question, what property which i must use to put that code? I wanted load that code after page.load ! if i put in aspxgridview.init its was loaded before page.load.and the output it must like this :

1 2 3 4 5 6
row row row row row row
row row row row row row

[code]....