Dynamic Checkbox problem when added in render method &checked=true

Discussion in 'ASP .Net' started by =?Utf-8?B?S2V2aW4gUg==?=, Jul 4, 2006.

  1. This is one of the weirdest problems I have ever run into. I have had to
    trim down a bunch of code to give a sample that is more easily readable by
    those who will view this. Here is the problem:

    I dynamically add an htmlcheckbox to a webform in the pages render and set
    the checked value to true. When the page loads, if I remove the check from
    the checkbox and then submit it, in the submit event the checkbox' checked
    value is still true. However if I orignally set the checked value to false in
    the render event, load the webform, check the checkbox and submit the page,
    in the submit event, the checkbox's value is set to true which is how I would
    expect it to work.

    In the example I am including, you will see 2 checkboxes are added in an if
    statement. This statement is so when the form loads for the first time, I
    can control having the checkboxes being added in the render event first
    instead of in the load and then the render (this is to emulate my situation
    and show the problem). The first checkbox is set to true and doesn't work
    properly, while the second is originally set to false and does work properly.

    This seems extremely odd that the one originally set to false works properly
    yet the one originally set to true does not. Is this a problem and is there
    a way to fix it.

    This problem only appears when the page is loaded the first time and
    submitted the first time. After this it works properly and I would guess
    this has something to do with the second time through loading in the
    page_load first instead of the render method first.

    For debugging purposes, set a break on the mbtnRefresh_ServerClick method
    and then watch the following values:
    mtblMain.Rows(0).Cells(0).Controls(0).ID
    ctype(mtblMain.Rows(0).Cells(0).Controls(0), HtmlInputCheckBox).Checked
    mtblMain.Rows(1).Cells(0).Controls(0).ID
    ctype(mtblMain.Rows(1).Cells(0).Controls(0), HtmlInputCheckBox).Checked


    'CODE BEHIND

    Imports System.Web.UI.HtmlControls

    Partial Class _Default

    Inherits System.Web.UI.Page

    Private WithEvents mbtnRefresh As New HtmlInputSubmit

    Private mobjTest As Object

    Private mtblMain As New HtmlTable

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

    Dim ltblMain As New HtmlTable

    mobjTest = HttpContext.Current.Session("mobjTest")

    mbtnRefresh.ID = "btnRefresh"

    form1.Controls.Add(mbtnRefresh)

    form1.Controls.Add(mtblMain)

    ListLayers()

    End Sub

    Protected Overrides Sub Render(ByVal writer As System.Web.UI.HtmlTextWriter)

    HttpContext.Current.Session("mobjTest") = New Object

    mobjTest = HttpContext.Current.Session("mobjTest")

    'Had to add this to the render section so we can obtain the new layers from

    'the MapViewer which is obtained during prerender

    ListLayers()

    MyBase.Render(writer)

    End Sub

    Private Sub ListLayers()

    Dim lcbxTemp As HtmlInputCheckBox

    Dim ltcTEmp As HtmlTableCell

    Dim ltrTemp As HtmlTableRow

    mtblMain.Controls.Clear()

    If mobjTest IsNot Nothing Then

    ltrTemp = New HtmlTableRow

    ltcTEmp = New HtmlTableCell

    lcbxTemp = New HtmlInputCheckBox

    lcbxTemp.ID = "test"

    lcbxTemp.Checked = True

    ltcTEmp.Controls.Add(lcbxTemp)

    ltrTemp.Controls.Add(ltcTEmp)

    mtblMain.Controls.Add(ltrTemp)

    ltrTemp = New HtmlTableRow

    ltcTEmp = New HtmlTableCell

    lcbxTemp = New HtmlInputCheckBox

    lcbxTemp.ID = "test2"

    lcbxTemp.Checked = False

    ltcTEmp.Controls.Add(lcbxTemp)

    ltrTemp.Controls.Add(ltcTEmp)

    mtblMain.Controls.Add(ltrTemp)

    End If

    End Sub

    Protected Sub mbtnRefresh_ServerClick(ByVal sender As Object, ByVal e As
    System.EventArgs) Handles mbtnRefresh.ServerClick

    End Sub

    End Class

    'WEBFORM

    <%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb"
    Inherits="_Default" %>

    <html xmlns="http://www.w3.org/1999/xhtml" >

    <head runat="server">

    <title>Untitled Page</title>

    </head>

    <body>

    <form id="form1" runat="server">

    </form>

    </body>

    </html>
    =?Utf-8?B?S2V2aW4gUg==?=, Jul 4, 2006
    #1
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  2. A bit more info:

    What am I trying to do:
    I am working on a mapping solution that has two controls. One is a map
    control and the other is a layers control. When the form first loads, I
    don''t know which layers the map control has available to it (I have
    simplified this above in the code that checks to see if mobjTemp isNot
    nothing) thus I cannot create the check boxes. When I get to the render of
    the layer control the map control now knows the layers that are available and
    thus I can create the checkboxes to turn layers on and off.



    The steps to follow:

    1. Add a breakpoint on the serverclick event for the button

    2. Load the form (this runs the form load which does not create the text
    boxes the first time through because mobjTest is nothing. The render method
    will then run which sets the mobjTest value thus creating the 2 checkboxes
    where the firstone is checked true and the second is checked false)

    3. Click on the first checkbox to remove the checkmark and click on the
    second checkbox to add the checkmark.

    4. Click submit. This will end up running the load event again. This time
    however, mobjTest is valid thus the checkboxes render. If I fail to create
    the checkboxes here, I am unable to obtain the value submitted from the form
    when the click event fires.

    5. In the serverclick event check the values of the checkboxes. You will
    see that the checkbox originally set to false is now true, but the checkbox
    originally set to true is still true. This is incorrect.

    This problem only appears when the page is loaded the first time and
    submitted the first time. After this it works properly.

    For debugging purposes, set a break on the mbtnRefresh_ServerClick method
    and then watch the following values:
    mtblMain.Rows(0).Cells(0).Controls(0).ID
    ctype(mtblMain.Rows(0).Cells(0).Controls(0), HtmlInputCheckBox).Checked
    mtblMain.Rows(1).Cells(0).Controls(0).ID
    ctype(mtblMain.Rows(1).Cells(0).Controls(0), HtmlInputCheckBox).Checked



    When I want to layers on and off, i do so and click a refresh button. In
    the load event I must recreate my checkboxes so that I may later obtain the
    submitted values in the serverclick event. When the serverclick event fires
    I take the layer values and tell the map which layers have been turned on and
    off. Here lies my problem. The first time a checkbox is dynamically added
    to the screen, its value is set to true and not originally created in the
    load event, setting the value to false will not be the submitted value.
    However if set to false when rendered it works fine.

    After the first load it works fine because after the first submit, you have
    now created that control in the load event.
    =?Utf-8?B?S2V2aW4gUg==?=, Jul 5, 2006
    #2
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