Why doesn't qty column increment when adding in textbox to datagridview in vb.net

Why doesn't qty column increment when adding in textbox to datagridview in vb.net.

so the qty column can only max the value to 2 is there something wrong with my code should continue to grow if the product code is the same as the product column in the DataGridView.

Thanks

 Private Sub BindItemDetail()
            If _myTable.Rows.Count = 0 Then
                Dim field() As String = {"No", "Codeproduct", "Barcode", "Qty"}
                _myTable = DataControl.CreateDataTableDynamic(field)
            End If
            grid.DataSource = _myTable
        End Sub
 Private Sub FillDataTable(iRow As Integer, ByVal Codeproduct As String, ByVal Barcode As String, ByVal Qty As Integer, ByVal Coledit As String, ByVal ColDel As String)

            Dim row As DataRow = _myTable.NewRow()
            row("No") = iRow
            row("Codeproduct") = Codeproduct
            row("Barcode") = Barcode
            row("Qty") = Qty
            _myTable.Rows.Add(row)
End Sub
Private Sub TextBox1_KeyPress(sender As Object, e As KeyPressEventArgs) Handles TextBox1.KeyPress
        Dim iRow As Integer
        If Grid.RowCount - 1 = 0 Then
            iRow = 1
        Else
            iRow = Convert.ToInt32(Grid.Rows(Grid.RowCount - 2).Cells(0).Value.ToString()) + 1
        End If
        Dim Qty As Integer = 1
        Dim Found As Boolean = False
        If e.KeyChar = Microsoft.VisualBasic.ChrW(Keys.Enter) Then
            For j = 0 To Me.Grid.Rows.Count - 1
                If Convert.ToString(Me.Grid.Rows(j).Cells(1).Value) = TextBox1.Text.ToString() Then
                    Found = True

'The problem in my code is in below the code line
                    Grid.Rows(j).Cells(3).Value = Qty + 1
                    TextBox1.Clear()
                    TextBox2.Clear()
                    Exit For
                End If
            Next
            If Not Found Then
                FillDataTable(iRow, TextBox1.Text, TextBox2.Text, Qty)
                Grid.DataSource = _myTable
                TextBox1.Clear()
                TextBox2.Clear()
            End If
        End If
    End Sub

Desired result

The problem with the code is you are setting the cell value to 2, not incrementing it. You set this:

        Dim Qty As Integer = 1

and then do this:

Grid.Rows(j).Cells(3).Value = Qty + 1

So if you actually want to increment the cell value by 1, then you would instead use this:

Dim newValue As Integer
If Integer.TryParse(Grid.Rows(j).Cells(3).Value, newValue) Then
    newValue += 1
Else
    newValue = 1
End If
Grid.Rows(j).Cells(3).Value = newValue.ToString()

and not define the Qty variable at all.

While at it, you probably want to check for the Enter key first, since it seems you don't want to do anything else in this method for other keys. This would be the revised code:

Private Sub TextBox1_KeyPress(sender As Object, e As KeyPressEventArgs) Handles TextBox1.KeyPress
    If e.KeyChar = Microsoft.VisualBasic.ChrW(Keys.Enter) Then
        Dim iRow As Integer
        If Grid.RowCount - 1 = 0 Then
            iRow = 1
        Else
            iRow = Convert.ToInt32(Grid.Rows(Grid.RowCount - 2).Cells(0).Value.ToString()) + 1
        End If
        Dim Found As Boolean = False
        For j = 0 To Me.Grid.Rows.Count - 1
            If Convert.ToString(Me.Grid.Rows(j).Cells(1).Value) = TextBox1.Text.ToString() Then
                Found = True
                Dim newValue As Integer
                If Integer.TryParse(Grid.Rows(j).Cells(3).Value, newValue) Then
                    newValue += 1
                Else
                    newValue = 1
                End If
                Grid.Rows(j).Cells(3).Value = newValue.ToString()
                TextBox1.Clear()
                TextBox2.Clear()
                Exit For
            End If
        Next
        If Not Found Then
            FillDataTable(iRow, TextBox1.Text, TextBox2.Text, 1)
            Grid.DataSource = _myTable
            TextBox1.Clear()
            TextBox2.Clear()
        End If
    End If
End Sub

I have to assume that if it is not found then the quantity should now be 1, but I don't have the specifications for your project, nor access to all of the objects, such as TextBox1, TextBox1, Grid, nor the FillDataTable method. If one presses Enter several times, this method would keep incrementing the value by 1.

EDIT: Per Dr. Null's suggestion, changed to ensure data type compatibility.

thanks for the guide @jmcilhinney

Grid.Rows(j).Cells(3).Value += Qty