Datagridview bound to object - Making the new rows appear blank

Question

I have a Datagridview that changes its content according to a selection the user makes in a listBox. The DGV consits of 2 comboboxes (Country, Product) and 1 textbox (Quantity).

I've created a class combined of 3 integers. This class is used as a type of list, which is the datasource for the DGV. There is also another list containing the prior list, so I have a list of datasources.

The DGV's datasource is a BindingSource that changes whenever the SelectedIndex of the listBox is fired.

My problem occurs whenever a new row is added to the DGV: I use the BindingSource.AddNew which calls the constructor of the class, but it must assign values to each item in the class. That way, whenever I click any cell in the DGV I don't get a blank row. Moreover, when the BS changes and then returned, another row is added.

What I want to get is a blank row - empty comboboxes and textbox.

Thanks for your help!

The class:

    Public Class PoList
    Private _CountryID As Integer
    Private _ProductID As Integer
    Private _Quantity As Integer

    Public Sub New(ByVal CountryID As Integer, ByVal ProductID As Integer, ByVal Quantity As Integer)
        _CountryID = CountryID
        _ProductID = ProductID
        _Quantity = Quantity
    End Sub

    Private Sub New()
        _CountryID = 1
        _ProductID = 2
        _Quantity = Nothing
    End Sub

    Public Property CountryID() As Integer
        Get
            Return _CountryID
        End Get
        Set(ByVal value As Integer)
            _CountryID = value
        End Set
    End Property

    Public Property ProductID() As Integer
        Get
            Return _ProductID
        End Get
        Set(ByVal value As Integer)
            _ProductID = value
        End Set
    End Property

    Public Property Quantity() As Integer
        Get
            Return _Quantity
        End Get
        Set(ByVal value As Integer)
            _Quantity = value
        End Set
    End Property

    Public Shared Function CreateNewPoList() As PoList
        Return New PoList
    End Function
End Class

Private Sub List_AddRow(ByVal sender As Object, ByVal e As AddingNewEventArgs) Handles AllListBindingSource.AddingNew
    e.NewObject = PoList.CreateNewPoList
End Sub

Creating a new inner list:

AllList.Add(New List(Of PoList))
AllListBindingSource.AddNew()
AllListBindingSource.DataSource = AllList(TableCounter)
AddPoDetails.DataSource = AllListBindingSource

SelectedIndexChanged event:

AllListBindingSource.DataSource = AllList(AddPoList.SelectedIndex)
AddPoDetails.DataSource = Nothing
AddPoDetails.DataSource = AllListBindingSource

Can you supply a snippet of how you create the DGV combobox columns and how the item table looks? — WozzeC, Dec 03 '12 at 14:52

score 0 · Answer 1 · answered Dec 03 '12 at 13:13

Right, lets see if I can help you. As I interpret it you have a list filled with lists. These lists don't know their own identity and is based on the current index in the list.

First of I wouldn't use Bindingsource.AddNew I would add the new object straight to the list instead.

AllList(TableCounter).Add(New Polist())

This way you know exactly how many objects has been created, by using events you aren't quite sure are you. To refresh the list do this:

AllListBindingSource.ResetBindings(true)

Which will update your DGV with the new line.

Now you need to restructure your class since when you create a new Polist you set a value to nothing. This will crash your table. What you need to do is this:

Private _Quantity As String

Public Property Quantity() As String
        Get
           Return _Quantity
        End Get
        Set(ByVal value As String)
           _Quantity = value
        End Set
End Property

Using a string is the only way for you to get a blank textbox, I would recommend you to have 0 as default if you are using Quantity as an integer (which you should). Your constructor needs to be changed to this:

Private Sub New()
  _CountryID = 0            
  _ProductID = 0            
  _Quantity = ""
End Sub

In your combobox columns you have to add a blank item in the top (I'm guessing your adding them manually), should be possible by having a blank row in the top of the items.

Thanks for the quick answer! The things is that these comboboxes are bound to a datatable, and the values cannot be strings - they have to be integers. — Gil, Dec 03 '12 at 13:41
So what you are saying are that you want a blank textbox and blank comboboxes. But you have set the entire thing up so that a blank textbox and blank comboboxes aren't allowed. Do you see the problem in your logic? — WozzeC, Dec 03 '12 at 13:59
My two cents, either change the setup completely or decide on a default state that you can consider as blank. — WozzeC, Dec 03 '12 at 14:01
I'm trying to achieve the same behaviour you get when you bind it to a DataTable. That's when you get the combobox filled with items but displaying the first empty item. — Gil, Dec 03 '12 at 15:30

Datagridview bound to object - Making the new rows appear blank

1 Answers1