prevent go to next row when duplicated value in `datagridview` - vb.net

Question

I have datagrid that user will add values in just one column , and i want to prevent duplicated data in this column, i had mange that by the code bellow,
what I want is to keep the selection (focus) in the same editing cell(x)
if the entered data is duplicated, so I tried to get the current row index and return to it if the data is duplicated but its not working.
row_index = DataGridView1.CurrentRow.Index.ToString()
Dim cell As DataGridViewCell = DataGridView1.Rows(row_index).Cells(1)
DataGridView1.CurrentCell = cell
DataGridView1.BeginEdit(True)
NOTE : User will Add barcode number, so he will use barcode scanner or add it manually and press enter key.
Private Sub DataGridView1_RowValidated(sender As Object, e As DataGridViewCellEventArgs) Handles DataGridView1.RowValidated
If DataGridView1.Rows.Count > 2 Then
Dim i As Integer = 0
Dim row_index As Integer
' loop condition will loop while the row count is less or equal to i
While i <= DataGridView1.Rows.Count - 1
Dim j As Integer = 1
' loop condition will loop while the row count is less or equal to j
While j <= DataGridView1.Rows.Count - 1
Dim str As String = DataGridView1.Rows(i).Cells(1).Value()
Dim str1 As String = DataGridView1.Rows(j).Cells(1).Value()
If Not str1 = "" AndAlso Not str = "" Then
If str1 = str Then
'row_index = DataGridView1.SelectedCells.Item(i).RowIndex.ToString()
row_index = DataGridView1.CurrentRow.Index.ToString()
Dim cell As DataGridViewCell = DataGridView1.Rows(row_index).Cells(1)
DataGridView1.CurrentCell = cell
DataGridView1.BeginEdit(True)
Exit Sub
End If
End If
j += 1
End While
i += 1
End While
End If
End Sub

Answer 1

You can try it also in a for loop. This is how I do it. If what you mean is to stop/retain the selection(focus) or go to in a cell/row whenever it is a duplicate with the current data you have. This should work fine.
enter code here
For i = 0 To Datagridview1.Rows.Count - 1
If Datagridview1.Rows(i).Cells(1).Value = DataYouWillInput Then
DataGridView1.CurrentCell = DataGridView1.Rows(i).Cells(1)
Exit for
End If
Next
enter code here

Answer 2

If your condition returns true with the condition of current data and data you'll be adding. Just exit your loop. Use this.
DataGridView1.CurrentCell = DataGridView1.Rows(i).Cells(1)