Composite Control with Templates - DropDownList bubble events

Discussion in 'ASP .Net Building Controls' started by Marc Castrechini, Sep 22, 2006.

  1. I have a base composite control that uses templates.

    If I add buttons (image, link, etc ..) to the template we can bubble the
    event as an item command using the following ...
    Protected Overrides Function OnBubbleEvent(ByVal source As Object, ByVal e
    As EventArgs) As Boolean

    If TypeOf e Is CommandEventArgs Then

    Dim cmd As CommandEventArgs = CType(e, CommandEventArgs)

    RaiseEvent ItemCommand(Me, New CommandEventArgs(cmd.CommandName,

    Return True

    End If

    Return False

    End Function

    Does anyone have a reference or know how to override and bubble up the
    SelectedIndexChanged event?

    Please note that the Autopostback="True" in the template and I don't have a
    member to wire up the event manually (although had considered looping
    through the template controls to do so).

    Final question, Is this group managed?


    - Castro
    Marc Castrechini, Sep 22, 2006
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  2. Hi Marc,

    The concept of event bubbling means taking unhandled events and shooting
    them up the chain of parent controls until they reach the surface. Event
    bubbling does not happen magically, it must be order by the controls when
    they fire their events. In the case of built-in ASP.NET controls, not all
    events order bubbleing to take place. Button, LinkButton, and ImageButton
    are those who do event bubbling. They have an event called Command. A
    button's Click event does not automatically bubble up, but its Command
    event does:

    Protected Overridable Sub OnClick(Byval e as EventArgs)
    RaiseEvent Click(Me, e)
    End Sub

    Protected Overridable Sub OnCommand(Byval e as CommandEventArgs)
    RaiseEvent Command(Me, e)
    RaiseBubbleEvent(Me, e)
    End Sub

    The DropDownList does not do event bubbling by default. You will have to
    create your own customized DropDownList to bubble event:

    Public Class MyDropDownList
    Inherits DropDownList

    Protected Overrides Sub OnSelectedIndexChanged(ByVal e As
    MyBase.RaiseBubbleEvent(Me, New
    CommandEventArgs("SelectedIndexChanged", Me))
    End Sub

    End Class

    Using this customized DropDownList in your templates content, then you can
    handle the ItemCommand event like this:

    Protected Sub t1_ItemCommand(ByVal sender As Object, ByVal e As
    System.Web.UI.WebControls.CommandEventArgs) Handles t1.ItemCommand
    If e.CommandName = "SelectedIndexChanged" Then
    Dim ddl As DropDownList = CType(e.CommandArgument, DropDownList)
    End If
    End Sub

    This newsgroup is managed. See for a
    complete list of managed newsgroups.

    Walter Wang (, remove 'online.')
    Microsoft Online Community Support

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    Walter Wang [MSFT], Sep 25, 2006
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  3. Thank you Walter,
    Although I haven't implemented it yet I do understand your recommended

    Do I understand correctly that only the button objects you listed support a
    Command event bubble? So I should use the recommended solution for all
    other objects (Datagrid, Lists objects, etc)?


    - Marc
    Marc Castrechini, Sep 26, 2006
  4. Hi Marc,

    For the built-in web controls, three of them are bubbling event by default:
    Button, ImageButton, and LinkButton.

    If you use Reflector to run command "Analyzer" on Control.RaiseBubbleEvent,
    you will see these:

    * Button.OnCommand
    * ImageButton.OnCommand
    * LinkButton.OnCommand

    OnCommand will be used by RaisePostBackEvents which means it will gets
    called when it's clicked and posted back.

    * DataGridItem.OnBubbleEvent
    * DataListItem.OnBubbleEvent
    * DetailsViewRow.OnBubbleEvent
    * FormViewRow.OnBubbleEvent
    * GridViewRow.OnBubbleEvent
    * Menu.OnBubbleEvent
    * MenuItemTemplateContainer.OnBubbleEvent
    * RepeaterItem.OnBubbleEvent

    These are actually good examples of how to bubbling up the events when you
    received bubbled event from your templated contents. Use RepeaterItem for
    example, when you put a control which is calling RaiseBubbleEvent inside
    the template, what you need to do is to override OnBubbleEvent and bubble
    them up again. The bubbled event from RepeaterItem will be handled in
    Repeater's overridden OnBubbleEvent:

    Protected Overrides Function OnBubbleEvent(ByVal sender As Object, ByVal e
    As EventArgs) As Boolean
    Dim flag1 As Boolean = False
    If TypeOf e Is RepeaterCommandEventArgs Then
    Me.OnItemCommand(DirectCast(e, RepeaterCommandEventArgs))
    flag1 = True
    End If
    Return flag1
    End Function

    I hope this helps you understand how the event bubbling works. For your
    last question, other than the Button, LinkButton, ImageButton controls, all
    other controls are not bubbling event up by default.

    I understand that your initial requirement is to handle controls' events
    which are placed inside your control's templates. Besides using event
    bubbling, you can use FindControl to find the controls inside the template
    using their ID, and hook up its event handler dynamically.

    Walter Wang (, remove 'online.')
    Microsoft Online Community Support

    When responding to posts, please "Reply to Group" via your newsreader so
    that others may learn and benefit from your issue.

    This posting is provided "AS IS" with no warranties, and confers no rights.
    Walter Wang [MSFT], Sep 27, 2006
  5. Hi Marc,

    I am interested in this issue. Would you mind letting me know the result of
    the suggestions? If you need further assistance, feel free to let me know.
    I will be more than happy to be of assistance.

    Have a great day!

    Walter Wang (, remove 'online.')
    Microsoft Online Community Support

    When responding to posts, please "Reply to Group" via your newsreader so
    that others may learn and benefit from your issue.

    This posting is provided "AS IS" with no warranties, and confers no rights.
    Walter Wang [MSFT], Sep 29, 2006
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