Dynamic GridView Template for Header that fires Sorting Event

Frinavale

I have implemented the ITemplate interface to dynamically "display" complicated data in a GridView.

For the life of me I cannot implement the template in such a way that when it is applied to Header Data it is displayed as a link that raises a Sorting Event upon postback.

In my InstantiateIn method I create a LinkButton for my Header. I have added a handler to the LinkButton that calls a method upon DataBinding. In that method I have attempted everything I could possibly think of to get the LinkButton to cause a Sorting Event upon postback.

Has anyone done this?

I have a work around (that doesn't use a template for the Header) so there's is no urgency to this. I'm just dying to know how to get this to work.

Thanks

-Frinny

Post Reply

Frinavale

I went back to researching how to wire up dynamically created links/buttons in a template to click (command) events because I was never able to get this to work in the past.

The first thing to note is that you Must create your columns in your Page Init Event.

If you do not do this, the events for the controls created dynamically in your template will be lost. They will post back to the server, but then the event cease to exist.

Another thing to note is that events are handled by the controls that they occur in. This means that you have to implement code that handles the event in your ITemplate class. If you want this to be handled in the Page that the template belongs to you will have to Bubble Up the event.

One last thing to note is that Click Events do not automatically bubble up for LinkButtons, Buttons and ImageButtons. Only the Command Event will bubble up.

The following is an example of some code that creates a template and bubbles up the Command Event of the link buttons in the template to the Page that the template belongs to:

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 Public Partial Class Practice

    Inherits System.Web.UI.Page

    Private _theSource As List(Of SomeClass)
 
    Private Sub Practice_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Init

        _theSource = New List(Of SomeClass)

        _theSource.Add(New SomeClass("first", "data 1"))

        _theSource.Add(New SomeClass("second", "data 2"))

        _theSource.Add(New SomeClass("third", "data 3"))

        _theSource.Add(New SomeClass("fourth", "data 4"))

        Session("_theSource") = _theSource
 
'Please note that we are creating the GridView's Columns in the Page Init event.

'This is important because if you do not create the columns at this stage in the

'page life cycle the event for the dynamic link buttons will be lost!
 
        Dim tf As New TemplateField

        tf.HeaderText = "My Stuff"
 
'My Template is a Private Class that implements the ITemplate Field

'See it's definition farther down in the code.

        Dim item As New MyTemplate()
 
'Assigning the function named "MyCommandHandlingFunction" to handle the templates LinkButtonCommand Event 

        AddHandler item.LinkButtonCommand, New CommandEventHandler(AddressOf MyCommandHandlingFunction)
 
'I was using the following in an attempt to bubble up the Click event for the 

'Dynamic Link Button but this will never happen because I discovered that 

'Only the Command Event will bubble up.

'        AddHandler item.LinkButtonClick, New EventHandler(AddressOf MyCommandHandlingFunction)
 
'Adding the item to the template field

        tf.ItemTemplate = item
 
'Creating the GridView's columns 

        myGrid.Columns.Add(tf)
 
    End Sub
 
'This method simply binds the data source to the data grid

    Private Sub DisplayGridView()

        If _theSource Is Nothing Then

            _theSource = Session("_theSource")

        End If

        myGrid.DataSource = _theSource

        myGrid.DataBind()

    End Sub
 
    Private Sub Practice_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreRender

        DisplayGridView()

    End Sub
 
'This method handles the Command Event that originates from the LinkButton

'In the Template

    Private Sub MyCommandHandlingFunction(ByVal sender As Object, ByVal e As CommandEventArgs)

        'e.CommandArgument contains "Sort"...we set this in the Template

    End Sub
 
'    Private Sub MyClickHandlingFunction(ByVal sender As Object, ByVal e As EventArgs)

'

'    End Sub
 
    Private Class MyTemplate

        Implements ITemplate

        'Expose the command event handler - when the command event handler is trapped internally this event is raised to inform the container

        Public Event LinkButtonCommand As CommandEventHandler

        'Public Event LinkButtonClick As EventHandler
 
        Public Sub InstantiateIn(ByVal container As System.Web.UI.Control) Implements System.Web.UI.ITemplate.InstantiateIn

            Dim text As New Label

            text.Style.Add("display", "block")

            text.Style.Add("width", "80px")

            text.Style.Add("float", "left")
 
            AddHandler text.DataBinding, AddressOf Me.BindText

            container.Controls.Add(text)
 
            Dim lnkBtn As New LinkButton

            lnkBtn.Style.Add("float", "left")

            AddHandler lnkBtn.DataBinding, AddressOf Me.BindLinkButtons

            'AddHandler lnkBtn.Click, New EventHandler(AddressOf Click)

            AddHandler lnkBtn.Command, New CommandEventHandler(AddressOf Command)

            container.Controls.Add(lnkBtn)

        End Sub
 
        Private Sub BindLinkButtons(ByVal sender As Object, ByVal e As EventArgs)

            Dim lnkBtn As LinkButton = CType(sender, LinkButton)

            Dim container As GridViewRow = CType(lnkBtn.NamingContainer, GridViewRow)

            Dim cellContent As String = DataBinder.Eval(container.DataItem, "Content").ToString

            lnkBtn.Text = cellContent

            lnkBtn.CommandArgument = "Sort"
 
        End Sub

        Private Sub BindText(ByVal sender As Object, ByVal e As EventArgs)

            Dim txt As Label = CType(sender, Label)

            Dim row As GridViewRow = CType(txt.NamingContainer, GridViewRow)

            Dim cellContent As String = DataBinder.Eval(row.DataItem, "Title").ToString

            txt.Text = cellContent + ": "

        End Sub
 
''This will crash because the only event that's bubbled up is the Command Event....which takes a parameter of CommandEventArgs

        'Private Sub Click(ByVal sender As Object, ByVal e As EventArgs)

        '    RaiseEvent LinkButtonClick(Me, e)

        'End Sub
 
'Handles the Command Event: 

'When the link button is clicked the Command event is bubbled up to the container, which happens to be this class.

'This method bubbles the event up to the next level so that the event can be

'handled in the Page.

        Private Sub Command(ByVal sender As Object, ByVal e As CommandEventArgs)

            RaiseEvent LinkButtonCommand(Me, e)

        End Sub

    End Class
 
'This class is used for the DataSource of the GridView

    Private Class SomeClass

        Private _title As String

        Private _content As String

        Public Property Title() As String

            Get

                Return _title

            End Get

            Set(ByVal value As String)

                _title = value

            End Set

        End Property

        Public Property Content() As String

            Get

                Return _content

            End Get

            Set(ByVal value As String)

                _content = value

            End Set

        End Property
 
        Public Sub New(ByVal theTitle As String, ByVal theContent As String)

            _title = theTitle

            _content = theContent

        End Sub

    End Class
 
End Class

The ASPX code for this page is:

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 <%@ Page Language="vb" AutoEventWireup="false" CodeBehind="Practice.aspx.vb" Inherits="ScratchPad.Practice" %>
 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 
<html xmlns="http://www.w3.org/1999/xhtml" >

<head runat="server">

    <title></title>

</head>

<body>

    <form id="form1" runat="server">

    <div>

        <asp:GridView ID="myGrid" runat="server"

                                  BorderColor="black"

                                  GridLines="Horizontal"

                                  BorderStyle="None"

                                  allowpaging="True"

                                  autogeneratecolumns="False"

                                  style="margin-left:auto; margin-right:auto;"

                                  width="200" EnableViewState="true"></asp:GridView>

    </div>

    </form>

</body>

</html>

Jack Hack

Frinny,

I've been grappling with this problem for several days before locating your informative post. Not only did you provide a working example but your explanation of the problem allowed me to understand why my original attempts to handle such events were not working. Priceless.

I made one small deviation, I found that I had to add the gridview_RowCommand event handler to process the commandName and commandArgument (and subsequent logic) passed by my link button.

My solution is within a visual web part but I'm not sure if this would account for the change.

Thanks again,

Jack

Frinavale

I'm not sure why you had to make that change but I'm glad that my post helped you. I know I spent a lot of time trying to figure this stuff out :)

Dynamic GridView Template for Header that fires Sorting Event

✓ answered by Frinavale

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