ASP.NET - Add rows to repeater at runtime

Question

Public Partial Class _Default
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        If Page.IsPostBack = False Then
            Dim ds1 As New List(Of Link)

            For i = 1 To x
                Dim h As New Link
                ds1.Add(h)
                h.Text = "ssss"
                h.URL = "yyyyy"
            Next

            rptMenu.DataSource = (ds1)
        Else
            rptMenu.DataSource = ViewState("ds1")
        End If

        rptMenu.DataBind()
    End Sub

    Protected Sub addFeild()

        Dim ds1 As List(Of Link) = rptMenu.DataSource
        Dim h As New Link
        ds1.Add(H)
        rptMenu.DataBind()
    End Sub

    Private Sub Menu_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreRender
        ViewState("ds1") = rptMenu.DataSource
    End Sub
End Class

 <asp:Repeater ID="rptMenu" runat="server">
        <ItemTemplate>
            <tr>
                <td><asp:TextBox CssClass="txtBox" ID="txtText" runat="server" Text='<%# Eval("Text") %>'></asp:TextBox></td>
                <td><asp:TextBox CssClass="txtBox" ID="txtLocation" runat="server" Text='<%# Eval("URL") %>'></asp:TextBox></td>
                <td><asp:Button ID="btnDelete" runat="server" Text="Delete" /></td>
            </tr>
        </ItemTemplate>
        <FooterTemplate>
            <tr><td colspan="3">
                <asp:Button ID="btnAdd" runat="server" Text="Add" OnClick="addFeild" />
            </td></tr></table>
        </FooterTemplate>
    </asp:Repeater>

This code adds row whin i click Add

However, it removes all changes.

How can I add rows to repeater without removing changes?

Answer 1

To solve this issue I used Reflector to confirm what was done by the Repeater when it handles adding rows itself, creating an ExtensibleRepeater that inherits from Repeater and allows one row to be added for each update. Its only issue is you can't use the footer concept because an added row appears after the footer when it is updated.

Deleting a row is handled by setting the relevant RepeaterItem's Visible to False.

IIRC the reason why you're losing data on callback is because you're calling DataBind even on callback, which resets all existing data, including user form data.

The code is proprietary, but as it is based upon Reflector's display of the .NET 2.0 Repeater, I can show you an edited version:

Imports System.ComponentModel
Imports System.Security.Permissions
Imports System.Web
Imports System.Web.UI
Imports System.Web.UI.WebControls

'''======================================================================
''' Class: ExtensibleRepeater
''' 
''' <summary>
'''   A <see cref="Repeater" /> that can be extended by one item.
''' </summary>
''' 
''' <remarks>
'''   BUG: If the <see cref="ExtensibleRepeater.FooterTemplate" /> is defined, the additional
'''  item will appear after it!
''' </remarks>
''' 
''' <revisionhistory>
'''   100907 MEH Created based upon reflection on Repeater.
''' </revisionhistory>
'''======================================================================
<snip>
Public Class ExtensibleRepeater
    Inherits Repeater

Private additionalItem As RepeaterItem
<snip>

'''---------------------------------------------------------------------
''' Function: AddNew
''' 
''' <summary>
'''   Adds another <see cref="RepeaterItem"></see> to the <see cref="ExtensibleRepeater"></see>.
''' </summary>
''' 
''' <param name="ItemData">
'''   The data item to associate with the <see cref="RepeaterItem"></see>.
'''  Ignored if <paramref name="UseDataSource"></paramref> is False.
''' </param>
''' <param name="UseDataSource">
'''   Indicates whether to use the specified data source.
''' </param>
''' 
''' <returns>The new <see cref="System.Web.UI.WebControls.RepeaterItem"></see>.</returns>
''' 
''' <exception cref="NotSupportedException">Called more than once.</exception>
''' 
''' <remarks>
'''   Currently can only be called once. Must be called again after
'''  <see cref="DataBind"></see> is called to recreate the additional item.
''' </remarks>
''' 
''' <revisionhistory>
'''   100907 MEH Created based upon reflection on the protected Repeater.CreateControlHierarchy.
''' </revisionhistory>
'''---------------------------------------------------------------------
Public Function AddNew(ByVal ItemData As Object, Optional ByVal UseDataSource As Boolean = True) As RepeaterItem

<snip>
    If additionalItem IsNot Nothing Then _
        Throw New NotSupportedException

<snip>
    additionalItem = CreateItem(dataItemCount, itemType, UseDataSource, ItemData)

<snip>
    Return additionalItem
End Function

'''---------------------------------------------------------------------
''' Property: Items
''' 
''' <summary>
'''   Gets a collection of <see cref="System.Web.UI.WebControls.RepeaterItem"></see>
'''  objects in the <see cref="ExtensibleRepeater"></see>.
''' </summary>
''' 
''' <returns>
'''   A collection of <see cref="System.Web.UI.WebControls.RepeaterItem"></see>
'''  objects. The default is an empty <see cref="System.Web.UI.WebControls.RepeaterItemCollection"></see>.
''' </returns>
''' 
''' <remarks></remarks>
''' 
''' <revisionhistory>
'''   100907 MEH Created.
''' </revisionhistory>
'''---------------------------------------------------------------------
<snip>
Public Overrides ReadOnly Property Items() As RepeaterItemCollection
    Get
        If additionalItem IsNot Nothing Then
            Dim newItems As New ArrayList(MyBase.Items)
            newItems.Add(additionalItem)
            Return New RepeaterItemCollection(newItems)
        End If
        Return MyBase.Items
    End Get
End Property

'''---------------------------------------------------------------------
''' Function: CreateItem
''' 
''' <summary>
'''   Creates a <see cref="System.Web.UI.WebControls.RepeaterItem"></see>
'''  with the specified item type and location within the <see cref="ExtensibleRepeater"></see>.
''' </summary>
''' 
''' <param name="ItemIndex">
'''   The specified location within the <see cref="ExtensibleRepeater"></see>
'''  to place the created item.
''' </param>
''' <param name="ItemType">
'''   A <see cref="System.Web.UI.WebControls.ListItemType"></see> that
'''  represents the specified type of the <see cref="T:System.Web.UI.WebControls.Repeater"></see>
'''  item to create.
''' </param>
''' <param name="DataBind">
'''   Indicates whether to use the specified data source.
''' </param>
''' <param name="DataItem">
'''   The data item to associate with the <see cref="RepeaterItem"></see>.
'''  Ignored if <paramref name="DataBind"></paramref> is False.
''' </param>
''' 
''' <returns>The new <see cref="System.Web.UI.WebControls.RepeaterItem"></see>.</returns>
''' 
''' <remarks></remarks>
''' 
''' <revisionhistory>
'''   100907 MEH Created from reflection on the private Repeater.CreateItem, with no changes.
''' </revisionhistory>
'''---------------------------------------------------------------------
Private Overloads Function CreateItem(ByVal ItemIndex As Integer, ByVal ItemType As ListItemType, ByVal DataBind As Boolean, ByVal DataItem As Object) As RepeaterItem
<snip>

'''---------------------------------------------------------------------
''' Property: FooterTemplate
''' 
''' <summary>
'''   Gets or sets the <see cref="System.Web.UI.ITemplate" /> that
'''  defines how the footer section of the <see cref="ExtensibleRepeater" />
'''  control is displayed.
''' </summary>
''' 
''' <value>
'''   A <see cref="System.Web.UI.ITemplate" /> that defines how the
'''  footer section of the <see cref="ExtensibleRepeater" /> control is
'''  displayed.
'''   The default value is Nothing.
''' </value>
''' 
''' <remarks>
'''   This property does not change the inherited behaviour. It is
'''  only overridden to highlight this missing feature:
'''   TODO: BUG: This will appear before an additional item if one is added.
''' </remarks>
''' 
''' <revisionhistory>
'''   100907 MEH Created.
''' </revisionhistory>
'''---------------------------------------------------------------------
<Obsolete("BUG: This will appear before an additional item if one is added.")> _
<Description("The template used for the footer. BUG: This will appear before an additional item if one is added."), _
 Browsable(False), DefaultValue(CStr(Nothing)), _
 PersistenceMode(PersistenceMode.InnerProperty), _
 TemplateContainer(GetType(RepeaterItem))> _
Public Overrides Property FooterTemplate() As ITemplate
<snip>

'''---------------------------------------------------------------------
''' Sub: DataBind
''' 
''' <summary>
'''   Binds the <see cref="ExtensibleRepeater"></see> control and all
'''  its child controls to the specified data source.
''' </summary>
''' 
''' <remarks>
'''   <see cref="AddNew"></see> must be called again to restore the
'''  additional item if it is needed.
''' </remarks>
''' 
''' <revisionhistory>
'''   100908 MEH Created.
''' </revisionhistory>
'''---------------------------------------------------------------------
Overrides Sub DataBind()
    additionalItem = Nothing
<snip>

End Class