add new row in gridview - asp.net

Question

UPDATE
from this i bind gridview
Public Function uplif() As DataTable
Dim dt As New DataTable()
gridvieew1.Visible = True
Try
dt.Columns.AddRange(New DataColumn(1) {New DataColumn("ID", GetType(Integer)),
New DataColumn("Name", GetType(String))}
Dim Content As String = Request.Form(textbox1.UniqueID)
For Each row As String In Content .Split(ControlChars.Lf)
If Not String.IsNullOrEmpty(row) Then
dt.Rows.Add()
Dim i As Integer = 0
For Each cell As String In row.Split(ControlChars.Tab)
If i > 1 Then
labelmessage.Text = "More than 2 columns not Allowed !!"
textbox1.Text = ""
Else
If cell.Trim() = "" Then
cell = "0"
End If
dt.Rows(dt.Rows.Count - 1)(i) = cell
i += 1
End If
Next
End If
Next
gridvieew1.DataSource = dt
gridvieew1.DataBind()
Catch Ex As Exception
labelmessage.CssClass = "alertNo"
labelmessage.Text = Ex.Message
End Try
Return dt
End Function
Protected Sub PasteToGridView(sender As Object, e As EventArgs)
uplif()
End Sub
now when i try to add new row like this
Private Sub AddNewRowToGrid()
Dim dt As DataTable = uplif()
Dim NewRow As DataRow = dt.NewRow()
dt.Rows.Add(NewRow)
gridvieew1.DataSource = dt
gridvieew1.DataBind()
End Sub
Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
AddNewRowToGrid()
End Sub
this shows same output like add new row and replace previous data which is already in gridview and also this shows an error
Object reference not set to an instance of an object.
after click on add new row
ID Name
where as i want like this
ID Name
1 abc
2 def
(here new empty row when click on button )

Answer 1

As was pointed out in a comment to your post, the problem is in these two lines:
Dim dt As New DataTable()
...
gridview1.DataSource = dt
That creates a brand new DataTable and binds the grid view to it. You don't copy data over, and you don't alter the existing gridview's table.
The correct fix here would be to get the DataTable from the gridview's DataSource and make any changes you need to to that. Don't create a new DataTable.

Answer 2

Get the already assigned DataSource and then add the Row. Do not add columns as it will be already present in your datasource
Private Sub AddNewRowToGrid()
Dim dt As gridview1.DataSource
Dim NewRow As DataRow = dt.NewRow()
dt.Rows.Add(NewRow)
gridview1.DataSource = dt
gridview1.DataBind()
End Sub
Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
AddNewRowToGrid()
End Sub