How to add postback function in Custom Server Controls

Discussion in 'ASP .Net Building Controls' started by ton, Jan 29, 2004.

  1. ton

    ton Guest

    In the procedure CreateChildControls I add several controls like check and
    textboxes, button link and so on. How can I get the postback respons on the
    button link:
    The functions:
    lblButtonLink_Command and lblButtonLink_Click will not be executed

    Please help

    ton, Jan 29, 2004
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  2. ton,
    what do you want to do with the caputred event ?
    If all you need to do is capture it and take action in your control itself
    then you can easily do this :
    1.In createchildcontrols as you add your control that posts back, a button
    control for example :
    Dim button1 As New Button()
    button1.Text = "Submit"
    'Notice the event handler defined below
    AddHandler button1.Click, AddressOf Me.ButtonClicked

    now define the buttonclicked sub in your control and take action there,
    everytime the button is clicked this will fire :
    Private Sub ButtonClicked(sender As [Object], e As EventArgs)
    'What to do when button is clicked
    End Sub
    Should work for you, however I havent tested, but theorically this is all
    you need if this is your requirement. This is useful if you need to take
    action without exposing the event to the container page, giving the
    consumers of your control no control, as this event is not exposed to them.

    for a complete example that digs deeper into this you might want to look at
    the following link :

    Instead if you need to expose this event to the page where your control
    sits, and exposed to the end users of your control then you will need to
    bubble it up .
    Here is a very nice example of how this can be done for composite controls
    on MSDN.
    Alessandro Zifiglio, Jan 29, 2004
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  3. ton

    ton Guest

    Thanks for you reply

    I've used the code you've send me. It did not work. I made my control a lot
    simpeler and the result was the same.
    It looked as if the button click event were not handled by te procedure of
    the addresoff statement:

    The code looks now like: (And I'm sure that the createchildcontrols is
    called instaed of the the buttonclick procedure)

    Protected Overrides Sub CreateChildControls()
    If Me.Page.IsPostBack Then ' this is what runs after the button click
    ''Exit Sub '' (if I use Exit sub, no control is displayed)

    End If

    But = New Button

    But.Text = "Submit"

    But.ID = ClientID & "X"


    AddHandler But.Click, AddressOf Me.ButtonClick

    ChildControlsCreated = True

    end Sub

    Private Sub ButtonClick(ByVal sender As Object, ByVal e As System.EventArgs)

    But = FindControl(ClientID & "X")

    But.Text = "xxxx"


    End Sub

    I've dimensioned the button But as a private control, did not help
    íve done this with the withevents keyword, no difference
    and i've dimensioned them in the procedures createchildrecords and

    no differences


    ton, Jan 29, 2004
  4. Should fire. It works for me. However i have noticed that you are trying to
    add controls in your button click. This will not work for you because during
    postback those controls wont be recreated. so set a flag in viewstate as you
    add the control.
    Also I have noticed that you are trying to retrieve the same button, the one
    that fired the event in its event click and add it to the controls
    collection. This is not what what you need to do, but simply have the same
    code run after postback. Whatever code you have in your createchildcontrols
    method will run after postback, so let it all run as is and remove the
    ispostback check in there --If that code is not run your event will never
    fire, this is because the viewstate of the control is restored when the
    control is reloaded into its container.

    Private Sub ButtonClick(ByVal sender As Object, ByVal e As System.EventArgs)
    Dim MyButton As New Button()
    MyButton = CType(sender, Button)
    context.response.write("Click event for " & & "Fired")
    End Sub\Composition2.vb&font=3

    This is another example :\Composition3.vb&font=3

    Alessandro Zifiglio, Jan 29, 2004
  5. ton, Look at the post "No events are fired in child controls". Jeffery has
    just pointed out how useful Implementing the InamingContainer interface
    really is, especially when you need events in child controls routed. This is
    why your events werent firing.

    Iimplement this interface, and do not try passing an explicit id to your
    control if you dont need it.

    At the moment i myself am having problems passing an explict id to child
    controls and i'm working on a workaround. Will postback when I do find a
    way. One good reason to want to pass an explicit id is when using a
    validator control and as you already know you need to pass your controls id
    to its "controlToValidate" property.

    If this is not your case then i dont see why it is important to pass an
    explicit ID

    Alessandro Zifiglio, Jan 30, 2004
  6. oops, no workaround. That InamingContainer Interface had me a little
    confused ;P
    Since this interface already makes control ids unique you just need to pass
    your id as is like = "button1" = "textbox1"
    and so forth.
    When trying to reference textbox1 for example just simply use its id
    Alessandro Zifiglio, Jan 30, 2004
  7. ton

    ton Guest

    thank you
    the event is fired now but what I had in my does not occur:
    What I do is the following:
    - I show a record contains of 10 fields. The properties are:
    Tablename, RecordID, ShowFields (just a list of the fields to show)
    now pressing a button should replace the existing recordcard by another
    record card. For example a record contains a Contact. One of the field is
    the (database)-link to the Customer. To click on that buttonlink, should
    replace the form with for example 10 fields of the customer. You can say it
    is a zoom function to the toplevel of the database.
    For me this is inportant because it let me navigate in the database.
    Another example:
    when I want to modify the link I want to replace the control with a search
    screen to show a list of customers, where the user can select one. Or to add
    a complete knew one.

    The question is: "Is this possible". I do not want the webdesigner to add
    several controls on the form or to add several forms to the project to
    handle these evenst.


    ton, Feb 2, 2004
  8. ton, Can you explain that again. Its not very clear what you want to do ;P

    Alessandro Zifiglio, Feb 2, 2004
  9. ton

    ton Guest

    suppose you want to plan an activity. You get a card wich contains several
    field like
    date, begintime, end time, description, customer, type of activity and so
    type of activity is a dropdonlist
    description a textbox
    and the customer fields points to a foreignkey with the customer-table (if
    it is filled in I just show the customer name)
    off cause i cannot use a drop down list because there will be hunderds or
    thoussends of customers in the database
    so when it is empty i can press a button to select one from a list (get e
    search screen and then look up)
    or i can add a new customer, in both situations I want to have a different
    from as the replacement of my original activity:
    - pick from a list will show me several search fields from the table
    customer inclusive a Search button
    - the add new customer will give me a recordcard with the important fields
    to define a new customer
    when the customer is add, or when the customer is selected from the list I
    replace this card by the original content where the customer field shows the
    name of the customer

    So instead of multiple screens i just use the same screens to collect the
    information to plan this activity

    i hope you can help


    ton, Feb 2, 2004
  10. still not clear to me. Instead of defining a scenario can you simplify it
    and explain it in terms of custom control building what is not working for
    you. Is your requirement to build a databound custom server control ? Are
    you looking into building a custom control that has similar functionality to
    the datagrid, datalist, repeater and so on --what have you been able to
    implement so far. Which parts are working and where are you stuck.

    Alessandro Zifiglio, Feb 2, 2004
  11. ton

    ton Guest

    what i want is that when the event of the button fires I would like to show
    a complete other card, not the 10 fields i've showen earlier but because of
    the click i would see details depending on the click this could be 5 fields
    from another record and another table. So existing added controls away, new
    controls inplace

    ton, Feb 2, 2004
  12. ton

    Arthur Mnev Guest

    My experience to you:

    1. You control must implement INamingContainer to create its own namespace
    for event routing
    2. you override CreateChildControl and construct them according to your
    rules. It might be tricky you must remember that

    Even though ASP.NET supports events it is still disconnected architecture
    therefore once a server sends you a page it completely forgets about you
    therefore, when you click on a button (or generate other event) what must
    happen is:
    1 - data sent to the server
    2 - server constructs control tree (it MUST construct the same control
    tree as you had when you outputted the controls /previous state)
    3 - It checks which control supposed to receive an event (__EVENTTARGET
    post variable contains the control name)
    4 - An event is raised on behalf of control
    5 - You capture the event

    3. Clear the control list (Controls.Clear())
    4. Load Conditions (or Cache) of your previous request (ViewState could be
    used to store them)
    5. Build Controls based on previous conditions (or cache) - by the time you
    get out of the CreateChildControls() your ChildControlsCreated flag will be
    set to true by the framework
    6. Event delegate will get executed
    7. Make sure your event handler alters the Control Condition and calls
    (this.ChildControlsCreated = false). what that will do is place an
    indication flag that controls have not been created, that will case the
    framework to re-run CreateChildControls;
    8. When CreateChildControls re-runs it Clears it's previous control list,
    loads up Build Conditions and Generates the controls. Except the build
    conditions are based now on your different Build conditions.

    It is like you will be running the page twice - once to build an old state,
    figure out what event to raise and raise that event. Once raised you will
    re-run everything to determine second state and alter your presentation.

    If that is not enough think about this. When an event is mapped to the
    hierarchy, the hierarchy must be in the same exact order as it has been
    before, otherwise an event will get mapped to the wrong control. This is
    where you get CorruptedViewState error messages. Consider this:

    User John (ctl1)
    User Jane (ctl2)
    User Jim (ctl3)

    Each of the users is a button

    You click on Jane, however, between the time you got the page and the time
    you clicked user Jane was deleted, a server will construct a list
    User John (ctl1)
    User Jim (ctl2)

    Check which control you were trying to route an event to - that would be
    ctl2; execute OnClick event delegate for User Jim. -

    - Hope this helps

    In summary - if you can avoid doing it do so - I had a catalog that was
    working the exact same way; after 3 months of production I changed it to
    redirect itself to its own page with Get Parameters instead of events. I did
    it because every load of a page resulted in 2X work for the server (previous
    state + current state).
    it also removed a lot of complexity. I also know of a few that created
    every! control on the page they might need and then made them visible or hid
    them. Personally I don't like that style.

    - Arthur
    Arthur Mnev, Feb 2, 2004
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