dynamic event handling within a custom control

[venablc]

Hi,

I have a custom control which contains (amongst other things) an imageButton.

I'm adding a handler to the "click" event of the imageButton however when the button is clicked the handler routine is not called.

Can anyone tell me where I am going wrong with this? should I be handling the click event in some other way?

here is my code:

Imports Microsoft.VisualBasic
Imports System.Web.UI.WebControls
Imports System.Web.UI

Namespace company.web.media
    Public Class movieThumbnail


        Inherits WebControl

        Private _duration As String
        Private _title As String
        Private _imageURI As String
        Private _movieID As Integer
        Private img As New ImageButton


        Public Property imageURI() As String
            Get
                Return Me._imageURI
            End Get
            Set(ByVal value As String)
                Me._imageURI = value
            End Set
        End Property
        Public Property title() As String
            Get
                Return Me._title
            End Get
            Set(ByVal value As String)
                Me._title = value
            End Set
        End Property

        Public Property duration() As String
            Get
                Return Me._duration
            End Get
            Set(ByVal value As String)
                Me._duration = value
            End Set
        End Property
        Public Property movieID() As Integer
            Get
                Return Me._movieID
            End Get
            Set(ByVal value As Integer)
                Me._movieID = value
            End Set
        End Property
        Protected Overrides Sub RenderContents(ByVal writer As System.Web.UI.HtmlTextWriter)

            Dim table As New Table


            'setup generic styling
            table.Font.Name = "verdana"
            table.BackColor = System.Drawing.Color.FromArgb(25, 25, 25, 25)
            table.ForeColor = Drawing.Color.LightGray
            table.Width = 107

            'add three rows
            table.Rows.Add(New TableRow)
            table.Rows.Add(New TableRow)
            table.Rows.Add(New TableRow)

            'add image to first row
            table.Rows(0).Cells.Add(New TableCell)
            table.Rows(0).Cells(0).ColumnSpan = 2
            img.ImageUrl = Me._imageURI
            img.Height = 100
            img.Width = 100
            img.Style.Add("cursor", "pointer")

            AddHandler img.Click, AddressOf imgClick

            table.Rows(0).Cells(0).Controls.Add(img)

            'add title to second row
            table.Rows(1).Cells.Add(New TableCell)
            table.Rows(1).Cells(0).Text = Me._title
            table.Rows(1).Cells(0).Font.Size = FontUnit.Point(8)

            'add duration to third row
            table.Rows(2).Cells.Add(New TableCell)
            table.Rows(2).Cells(0).Text = Me._duration
            table.Rows(2).Cells(0).Font.Size = FontUnit.Point(10)

            'render control
            table.RenderControl(writer)

        End Sub


        Private Sub imgClick(ByVal sender As Object, ByVal e As ImageClickEventArgs)
            MsgBox(Me._movieID)
        End Sub

    End Class


End Namespace

and the markup simply:

<l11:movieThumbnail runat="server" duration="14:42" title="move title" imageURI="http://www.google.co.uk/logos/newton10-tree.jpg" />

[gep13]

Hey,

To start with, as a general rule, it is bad practice to use a MsgBox for debugging purposes. Use debug/trace writes instead.

Have you set a break point in the click event? Does it ever get hit?

Gary

[venablc]

No, the breakpoint is not hit within the triggered routine (imgClick()) but the breakpoint is hit on the line which adds the handler.

[gep13]

Hey,

I believe I am correct in saying that the AddHandler call is being placed in the wrong place. This needs to be done earlier in the page life cycle, otherwise it will never get hit.

It has been a while, but I would have thought in the CreateChildControls overridden method.

Gary

[venablc]

I have overridden the createChildControls() routine as suggested and added in the line which adds the handler (see code below) however I am still getting the same result. The addhandler line does ger hit however when the button is clicked the imgClick routine does not get hit

      Protected Overrides Sub CreateChildControls()
            MyBase.CreateChildControls()
            AddHandler img.Click, AddressOf imgClick
        End Sub
        Protected Overrides Sub RenderContents(ByVal writer As System.Web.UI.HtmlTextWriter)

            Dim table As New Table


            'setup generic styling
            table.Font.Name = "verdana"
            table.BackColor = System.Drawing.Color.FromArgb(25, 25, 25, 25)
            table.ForeColor = Drawing.Color.LightGray
            table.Width = 107

            'add three rows
            table.Rows.Add(New TableRow)
            table.Rows.Add(New TableRow)
            table.Rows.Add(New TableRow)

            'add image to first row
            table.Rows(0).Cells.Add(New TableCell)
            table.Rows(0).Cells(0).ColumnSpan = 2
            img.ImageUrl = Me._imageURI
            img.Height = 100
            img.Width = 100
            img.Style.Add("cursor", "pointer")



            table.Rows(0).Cells(0).Controls.Add(img)

            'add title to second row
            table.Rows(1).Cells.Add(New TableCell)
            table.Rows(1).Cells(0).Text = Me._title
            table.Rows(1).Cells(0).Font.Size = FontUnit.Point(8)

            'add duration to third row
            table.Rows(2).Cells.Add(New TableCell)
            table.Rows(2).Cells(0).Text = Me._duration
            table.Rows(2).Cells(0).Font.Size = FontUnit.Point(10)

            'render control
            table.RenderControl(writer)

        End Sub

any other ideas?

[gep13]

Hey,

I would suggest that you start with a known working example, i.e:

http://www.dotnetjohn.com/articles.aspx?articleid=126

Get that up and running, then start to edit it to suit your needs.

Gary

[mendhak]

Recreate those controls, or at least the img, in the Init event of your ASCX. Right now, when the postback occurs, the dynamic control's viewstate isn't reassigned. If you do it in the Init, the viewstate gets assigned, the page then realizes that the event needs to be raised.

More Info

[venablc]

Hi,

Thanks for your help mendhak and gep13. Implementing iNamingContainer fixed the issue (maybe someone could explain why?). I got this by comparing the example you sent gep13.

the solution you suggested mendhak also worked, creating the control in the init routine instead of the overidden createChildControls() routine.

Thanks again

Chris V

[mendhak]

INamingContainer ensures that the names are unique and I think it maintains the names across postbacks too (so that viewstate can be assigned to it), which is effectively the same thing. I haven't used it to maintain viewstate before though, I usually use Init.