FAQ: Why do dynamic controls disappear on postback and not raise events? RSS

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  dch3

  Member

  447 Points

  638 Posts

  Re: FAQ: Why do dynamic controls disappear on postback and not raise events?

  Sep 29, 2009 06:58 PM|LINK

  From personal experience, I nearly killed myself over trying to sort out problems that I had with adding ListItems to a Drop Down List in a repeater. The code seemed to work perfectly fine outside of the repeater with the ListItems being persisted and the _SelectedIndexChanged event being raised and other what not. I finally figured out that instead of having the Drop Down List in the markup and adding the ListItems to it, that I needed to just have an asp : placeholder in the content and the create the entire Drop Down List from start to finish in the code behind via the _ItemDataBound event. I had checked everything including EnableViewState on the control, on the Repeater on the Page.

  
  

  Of course now that its working, the whole thing has to be scrapped given that I didn't factor in how the number of items in the repeater and the Drop Down List would impact the load time of the page
  

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  girish dagdi...

  Member

  45 Points

  49 Posts

  Re: FAQ: Why do dynamic controls disappear on postback and not raise events?

  Oct 08, 2009 06:30 AM|LINK

   hi,

  nice article.But i have different problem here.

   I am creating one tabcontainer and 13 tabpanels dynamically in page_init.I have also created iframe in each tabpanel dynamically in page_init.Now how can i access first iframe's id.I am getting only last iframe's id once page loads.

  The mypage.aspx.cs code is:

  using System;
  using System.Collections.Generic;
  using System.Linq;
  using System.Web;
  using System.Web.UI;
  using System.Web.UI.WebControls;
  using System.Data.SqlClient;
  using AjaxControlToolkit;
  using System.Configuration;

   

  public partial class Courses : System.Web.UI.Page
  {
      SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);
      SqlConnection conWeb = new SqlConnection(ConfigurationManager.ConnectionStrings["MainConnectionString"].ConnectionString);
      protected UpdatePanel upanel, MainPanel;
      public TabContainer MainTabcontainer, tabcontainer;
      public TabPanel tabpanel;
      public System.Web.UI.HtmlControls.HtmlGenericControl frame;
      public Label lblpage=new Label();
      int counter = 0;

     

     
      protected void Page_Load(object sender, EventArgs e)
      {
          Label myLable, myLable1;
          myLable = (Label)Master.FindControl("Label1");
          myLable.Text = "Courses  ";
          myLable1 = (Label)Master.FindControl("Label2");
          myLable1.Text = "";

        

      }
      protected void Page_Init(object sender, EventArgs e)
      {
          Label myLable, myLable1;
          myLable = (Label)Master.FindControl("Label1");
          myLable.Text = "";
          myLable1 = (Label)Master.FindControl("Label2");
          myLable1.Text = "";

          funShowData();
      }
      public void funShowData()
      {

          SqlCommand cmd = new SqlCommand("SELECT  query to access ids", con);
          con.Open();
          SqlDataReader sdr = cmd.ExecuteReader();
          int i = 0;

          MainPanel = new UpdatePanel();
          MainTabcontainer = new TabContainer();
          MainTabcontainer.Width = 660;

          while (sdr.Read())
          {
             
              tabpanel = new TabPanel();
              tabpanel.ID = "tab" + i.ToString();
              tabpanel.EnableViewState = true;
              tabpanel.HeaderText = sdr[1].ToString();
              tabpanel.Enabled = true;

              string val = sdr[0].ToString();
              if (val.Length == 1)
              {
                  val = "0" + val;
              }

              tabpanel.TabIndex = Convert.ToSByte(val);
              upanel = new UpdatePanel();

              upanel.ID = "upanel";
              tabcontainer = new TabContainer();

  
             
              tabcontainer.EnableViewState = true;

              upanel.ContentTemplateContainer.Controls.Add(tabcontainer);
              tabpanel.Controls.Add(upanel);
            

              frame = new System.Web.UI.HtmlControls.HtmlGenericControl("iframe");
              frame.ID = "frame"+counter;
              frame.EnableViewState = true;
              frame.Attributes.Add("frameborder", "0");
              frame.Attributes.Add("src","Tabs/pr_tab.aspx");
              frame.Attributes.Add("width", "630px");
              frame.Attributes.Add("height", "385px");
              tabpanel.Controls.Add(frame);

  
              Label1.Text = "Counter "+counter;
              MainTabcontainer.Tabs.Add(tabpanel);
              i++; counter++;

          }
          sdr.Close();
          con.Close();
          MainPanel.ContentTemplateContainer.Controls.Add(MainTabcontainer);
          div1.Controls.Add(MainPanel);
      }
      protected void ImageButton_download_Click(object sender, ImageClickEventArgs e)
      {
            
          if (MainTabcontainer.ActiveTabIndex == 0)
          {
              Label myLable, myLable1;
              myLable = (Label)Master.FindControl("Label1");
              myLable.Text = "Course > ";
              myLable1 = (Label)Master.FindControl("Label2");
              myLable1.Text = "DVLSI > e-brochure ";
              

              ScriptManager.RegisterStartupScript(Page, this.GetType(), "getfun", "javascript:getfun(" + MainTabcontainer.ActiveTabIndex + ");", true);//To register client script

              

          }
      }
      
     

  
  }

   

  mypage.aspx:

  <asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">

     <script type="text/javascript">
     function getfun(index)
     {
   var div=$get("<%= div1.ClientID%>",document);
   var  Tabcontainer=$get("<%= MainTabcontainer.ClientID%>",div);
    var  frame=$get("<%= frame.ClientID%>",Tabcontainer.ActiveTabIndex);
   

   alert(frame.id);
     }
     </script>
    
      <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
      <div id="div2" runat="server" style="float:left">
          <table>
          <tr>
              <td style="border: 1px solid #3399FF; height: 435px; width: 70px; "
                  valign="top">
                  <br />
                  <br />
                  <asp:ImageButton ID="ImageButton_download" runat="server" ImageUrl="~/Images/arrows.gif"
                      OnClick="ImageButton_download_Click" />
                  <br />
                  <br />
                  
              </td>
          </tr>
      </table>
  </div>
      <div id="div1" runat="server" style="float:right">
     
    
     
    
      </div>
     
  </asp:Content>

   

  In function getfun(index),how can i access first tabpanels iframe.

  dynamic controls

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  batool

  Member

  32 Points

  100 Posts

  Re: FAQ: Why do dynamic controls disappear on postback and not raise events?

  Oct 14, 2009 08:22 AM|LINK

  I tried to convert this code to C#, but its not working... Can anybody convert it?

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  miteshsura

  Member

  41 Points

  26 Posts

  Re: FAQ: Why do dynamic controls disappear on postback and not raise events?

  Oct 14, 2009 04:47 PM|LINK

  try this link .. http://www.developerfusion.com/tools/convert/vb-to-csharp/

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  batool

  Member

  32 Points

  100 Posts

  Re: FAQ: Why do dynamic controls disappear on postback and not raise events?

  Oct 14, 2009 07:51 PM|LINK

  miteshsura

  try this link .. http://www.developerfusion.com/tools/convert/vb-to-csharp/

  
  

  I have already tried this site... I got some problems in the "DynamicControlSelection" Method

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  rlnd

  Member

  6 Points

  8 Posts

  Re: FAQ: Why do dynamic controls disappear on postback and not raise events?

  Oct 25, 2009 06:05 PM|LINK

  Is it possible that this approach doesn't work for custom events? I've got a ul to which I'm programmatically adding (ASP.net user control) lis. I'm re-adding these user controls in the Page_Load event and 'ordinary' events (that is: LinkButton.Clicks) work fine - only my custom events somehow lose their handlers during the postback.

  Here is how I'm adding the controls to the list (the IDs are persistent over postbacks):

  Newsletter_TextPart control = (Newsletter_TextPart)LoadControl("~/Newsletter/TextPart.ascx");
          control.ID = "part_" + value.PartID;
  
  
  
  
          control.Deleted += new Newsletter_TextPart.DeletedEventHandler(part_Deleted);
  
  
          AsyncPostBackTrigger t2 = new AsyncPostBackTrigger();
          t2.ControlID = control.ID;
          t2.EventName = "Deleted";
  
  
          upnlText.Triggers.Add(t2);
  
  
  
  
          ulTextParts.Controls.Add(control);
          control.Part = value;

  
  Here is the relevant code in the UserControl:

      public delegate void DeletedEventHandler(object sender, PartEventArgs e);
  
      public event DeletedEventHandler Deleted;
  
      protected void lbtDelete_Click(object sender, EventArgs e)
      {
          if (Deleted != null)
              Deleted(this, new PartEventArgs(Part)); //'Part' is a property of the control
      }

  
  
  

  User Control event ASP.net 3.5 event handler

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  prakashshama...

  Member

  4 Points

  2 Posts

  Re: dynamic control help plzzzzzzzzzzzzzzz.....

  Oct 28, 2009 09:07 AM|LINK

  amitha

  this is my program logic

  i am new to this web developement so looking forward for your help

  plzzzzzzzzzz go thru

  reply asap

  having error with find control part

  do suggest all changes nedeed

  or else

  if possible  can u modify  my code n send rest of my project is going good i am really stuck with this plzz

  i hav to take values frm text box n calculate base on it

  
  

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

  <asp:Panel id="pnlone" runat="server" Height="74px" Width="384px">

  <asp:Label ID="lblAmnt" Text=" Enter the pension amount:" runat="server" Width="180px"></asp:Label>

  <asp:TextBox id="tbAmnt" runat="server"/><br />

  <asp:Label ID="lblNo" Text=" Enter the number of persons:" runat="server" Width="180px"></asp:Label>

  <asp:TextBox id="tbNo" runat="server"/><br />

  <center> <asp:button id="Enter" text="Enter" OnClick="SubmitBtn_Click" runat="server"/></center><br />

  <p><asp:PlaceHolder id="Area1" runat="server"></asp:PlaceHolder></p>

  <table id="tblReslt" runat="server">

  <tr>

  <td id="col1" runat="server"></td>

  <td id="col2" runat="server"></td>

  </tr>

  <tr>

  <td><asp:Button ID="submit" runat="server" visible="false" OnClick="calInheritAmnt" Text="submit" /></td>

  </tr>

  </table>

  </asp:Panel>

   

  <asp:table id="tblInheritDetails" runat="server" width="100%"/>

  </form>

   

  Partial Class testajax

  Inherits System.Web.UI.Page

  Sub Page_Load(ByVal Sender As Object, ByVal E As EventArgs)

  If IsPostBack Then

  SubmitBtn_Click(Sender, E)

  End If

  End Sub

  Public Sub SubmitBtn_Click(ByVal Sender As Object, ByVal E As EventArgs)

  Dim I As Integer

  For I = 1 To CInt(tbNo.Text.Trim())

  Dim tbInhrtrName As New TextBox

  tbInhrtrName.ID = "tbDynamic" & I.ToStringtbInhrtrName.Text = "Control" & I

  Form.Controls.Add(tbInhrtrName)

  'Area1.Controls.Add(tbInhrtrName)

  Dim MyLiteral = New LiteralControl

  MyLiteral.Text = "<BR><BR>"

  Form.Controls.Add(MyLiteral)

  'Area1.Controls.Add(MyLiteral)

  Next

  submit.Visible = "true"

  tblInheritDetails.Visible = "true"

  End Sub

  Protected Sub calInheritAmnt(ByVal sender As Object, ByVal e As System.EventArgs) Handles submit.Click

  Dim id As String

  Dim I As Integer

  'Dim tb As New TextBox

  For I = 1 To CInt(tbNo.Text.Trim())

  Dim tb As New TextBox

  id = "tbDynamic" & I.ToStringtb = DirectCast(sender, TextBox)

  Response.Write(tb.Text.ToString())

  'Response.Write(Session(id) & "<br/>")

  Next

  End Sub

  End Class

  
  

• • Reply
  

  girish dagdi...

  Member

  45 Points

  49 Posts

  Re: dynamic control help plzzzzzzzzzzzzzzz.....

  Oct 29, 2009 05:11 AM|LINK

  hi,

  you have written --  having error with find control part

  but where is the code for finding control.

  dynamic controls

• • Reply
  

  mausimo

  Member

  118 Points

  132 Posts

  Re: dynamic control help plzzzzzzzzzzzzzzz.....

  Nov 05, 2009 04:36 PM|LINK

  For everyone that wanted viewstate code in C#....

  const bool CREATE_SELECTED = true;
      const bool VIEW_SELECTED = true;
      const bool CURRENT_SELECTED = true;
  
  
      //store property value in viewstate so that it will survive postbacks
       private bool p_Create
       {
           set
           {
              ViewState["CREATE_SELECTED"] = value;
           }
           get
           {
              return Convert.ToBoolean(ViewState["CREATE_SELECTED"]);
           }
        }
  
  
       private bool p_View
       {
           set
           {
               ViewState["VIEW_SELECTED"] = value;
           }
           get
           {
               return Convert.ToBoolean(ViewState["VIEW_SELECTED"]);
           }
       }
  
  
       private bool p_Current
       {
           set
           {
               ViewState["CURRENT_SELECTED"] = value;
           }
           get
           {
               return Convert.ToBoolean(ViewState["CURRENT_SELECTED"]);
           }
       }

  
   

   protected void Page_Load(object sender, EventArgs e)
      {
          if (p_Create)
          {
              this.CreateWasClicked();
          }
          if (p_View)
          {
              this.ViewWasClicked();
          }
          if (p_Current)
          {
              this.CurrentWasClicked();
          }       
      }

  
   

      /// <summary>
      /// button used to view the view Articles
      /// </summary>
      protected void btnView_Click(object sender, EventArgs e)
      {
          //if the add article interface is already visible then hide it
          if (PlaceHolder_View.Visible == true)
          {
              PlaceHolder_View.Visible = false;
              btnView.Text = "View";
  
              //VERY IMPORTANT -> remember that we created these controls for the next postback
              this.p_View = false;
          }
          //if the add article interface is not visible then show it
          else
          {
              //displaying the add/create arcticle interface
              PlaceHolder_View.Visible = true;
              //changing button text to hide the create article interface.
              btnView.Text = "Hide View";
  
              //VERY IMPORTANT -> remember that we created these controls for the next postback
              this.p_View = true;
          }
      }
  
      /// <summary>
      /// for keeping view visible after post back if it was clicked
      /// </summary>
      protected void ViewWasClicked()
      {
          PlaceHolder_View.Visible = true;
      }

  
  This is the jist of using viewsates to keep post back variables in C#. This is from my code, it is showing you how to use the functionality. Manipulate this how you want, you can use any type (does not have to be bool etc).

  Good-Luck

  -Mike 

• • Reply
  

  jamesdeepak

  Member

  112 Points

  59 Posts

  Re: FAQ: Why do dynamic controls disappear on postback and not raise events?

  Mar 11, 2010 02:43 PM|LINK

  that code was really understandbable , had no problem converting that to C# .So this is why my Controls started disappearing Lol.

  thanks a bunch for the explanation.
  

  Wanna learn Microsoft Ajax client library? part 2 is here http://deeptechtons.com/tutorials/item/microsoft-ajax-series-part-two.html