Set Min value in NumericUpDown control in VB.Net

Hi kana250688,

In order to keep NumericUpDown control value 1, you need to set the Minimum property of NumericUpDown control to 1.

And to check whether the DataGridView has data or not on Button click event, you have to perform a check to know the count of rows in the DataGridView as below.

Private Sub btnPlusQty_Click(ByVal sender As Object, ByVal e As EventArgs)
    If dataGridView1.Rows.Count > 0 Then
        Dim product = GetProduct()
        If product IsNot Nothing Then
            product.Quantity += npQuantity.Value
            dataGridView1.Refresh()
        End If
    End If
End Sub

Private Sub btnMinusQty_Click(ByVal sender As Object, ByVal e As EventArgs)
    If dataGridView1.Rows.Count > 0 Then
        Dim product = GetProduct()
        If product IsNot Nothing Then
            If npQuantity.Value > 0 Then
                product.Quantity -= npQuantity.Value
            End If
            dataGridView1.Refresh()
        End If
    End If
End Sub

Hi kana250688,

Yo need to add one more condition as below to check if Quanity column value is 0. 

If product IsNot Nothing And product.Quantity > 0 Then

And you will need to use  ValueChanged event of NumericUpDown control to change the Quantity.

Refer below code.

Private Sub btnMinusQty_Click(ByVal sender As Object, ByVal e As EventArgs)
    If dataGridView1.Rows.Count > 0 Then
        Dim product = GetProduct()

        If product IsNot Nothing And product.Quantity > 0 Then
            product.Quantity -= npQuantity.Value
            dataGridView1.Refresh()
        End If
    End If
End Sub

Private Sub BtnAddproduct_Click(ByVal sender As Object, ByVal e As EventArgs)
    Dim List As List(Of Product) = New List(Of Product)()
    List.Add(New Product() With {
        .Code = "A",
        .Quantity = 2
    })
    List.Add(New Product() With {
        .Code = "B",
        .Quantity = 2
    })
    Dim bindingList As BindingList(Of Product) = New BindingList(Of Product)(List)
    dataGridView1.AutoGenerateColumns = True
    dataGridView1.AllowUserToAddRows = False
    bindingSource = New BindingSource() With {
        .DataSource = List
    }
    dataGridView1.DataSource = bindingSource
End Sub

Private Sub npQuantity_ValueChanged(ByVal sender As Object, ByVal e As EventArgs)
    If dataGridView1.Rows.Count > 0 Then
        Dim product = GetProduct()

        If product IsNot Nothing And product.Quantity > 0 Then
            product.Quantity = npQuantity.Value
            dataGridView1.Refresh()
        End If
    End If
End Sub

 Screenshot

steven says:

And you will need to use  ValueChanged event of NumericUpDown control to change the Quantity.

Remove the ValueChanged event of NumericUpDown control.

And if you want last value to be 1 on Minus Button click, you just have to change the value 0 to 1 in IF condition.

Refer below code.

Private Sub btnMinusQty_Click(ByVal sender As Object, ByVal e As EventArgs)
    If dataGridView1.Rows.Count > 0 Then
        Dim product = GetProduct()

        If product IsNot Nothing And product.Quantity > 1 Then
            product.Quantity = product.Quantity - 1
            dataGridView1.Refresh()
        Else
            MessageBox.Show("Quantity column cannot be minus")
        End If
    End If
End Sub

Screenshot