Remove item from DataSource when DataList ItemCommand is fired

Question

Im a little stuck here. I have a datalist which has a datasource thats a Lit (of SomeObject).

Private MyObjectList As List (of SomeObject)

I load data as and when required by the user clicking a button to add a product to their shopping basket and bind the datalist.

Form_load....
dl.Datasource = MyObjectList
dl.databind()
End Sub

To display data in the datalist i have a label which shows what theyve added, using the e eventArg casting it to my object, example below:

Protected Sub dl_ItemDataBound(sender As Object, e As System.Web.UI.WebControls.DataListItemEventArgs) Handles dl.ItemDataBound
    Dim myObject = DirectCast(e.Item.DataItem, SomeObject)
....
Label.Text = myObject.Description

End Sub

The inline code is:

    <asp:DataList ID="dl" runat="server">
                <ItemTemplate>
                    <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
                    <asp:Button ID="DeletePRoduct" runat="server" Text="Delete" CommandName="Del" CommandArgument='<%# Container.ItemIndex %>'/>
        </ItemTemplate>
    </asp:DataList>

So now i would like the user to be able to delete a product

Protected Sub dl_ItemCommand(source As Object, e As System.Web.UI.WebControls.DataListCommandEventArgs) Handles dl.ItemCommand
    Dim myObject = DirectCast(e.Item.DataItem, SomeObject)

    If e.CommandName = "Del" Then
        MyObjectList.Remove(myObject)
    ....
    End If
End Sub

If i try and pass in myObject under the ItemCommand i realised that e.item.DataItem that i casted is Nothing so it doesnt delete any products. I then thought to remove that product by row index and added a CommandArgument to the button when i realised i cant do that as the List expects a type of SomeObject.

Could anyone advise how to remove an object in this manner?

Thanks

Answer 1

You can find ID of deleting item using dl.DataKeys[e.Item.ItemIndex]. Make sure to set DataKeyField of DataList control.

<asp:DataList ID="dl" runat="server" DataKeyField="ID"...>
 ....
</asp:DataList>

Public Class SomeObject
    Public Property ID() As Integer
        Get
            Return m_ID
        End Get
        Set
            m_ID = Value
        End Set
    End Property
    Private m_ID As Integer
    Public Property Name() As String
        Get
            Return m_Name
        End Get
        Set
            m_Name = Value
        End Set
    End Property
    Private m_Name As String
End Class

Private _someObjects As List(Of SomeObject)
Public Property SomeObjects() As List(Of SomeObject)
    Get
        If _someObjects Is Nothing Then
            _someObjects = New List(Of SomeObject)() With { _
                New SomeObject() With { _
                    .ID = 1, _
                    .Name = "One" _
                }, _
                New SomeObject() With { _
                    .ID = 2, _
                    .Name = "Two" _
                }, _
                New SomeObject() With { _
                    .ID = 2, _
                    .Name = "Three" _
                } _
            }
        End If
        Return _someObjects
    End Get
    Set
        SomeObjects = value
    End Set
End Property

Protected Sub Page_Load(sender As Object, e As System.EventArgs)
    If Not IsPostBack Then
        dl.DataSource = SomeObjects
        dl.DataBind()
    End If
End Sub

Protected Sub dl_ItemCommand(source As Object, e As DataListCommandEventArgs)
    If e.CommandName = "Del" Then
        Dim id = Convert.ToInt32(dl.DataKeys(e.Item.ItemIndex))
        Dim someObject = SomeObjects.First(Function(x) x.ID = id)
        SomeObjects.Remove(someObject)

        dl.DataSource = SomeObjects
        dl.DataBind()
    End If
End Sub

Note: you need to take care of the persistence of data after deleting. For example, storing data in ViewState, Session or Database.