IPostBackDataHandler not working properly with DataGrid

Discussion in 'ASP .Net Building Controls' started by buzlite, Aug 11, 2006.

  1. buzlite

    buzlite Guest

    Hello All,


    I've posted this in
    microsoft.public.dotnet.framework.aspnet.datagridcontrol but got not
    reply so I'll try my luck here.

    Any help would be greatly appreciated.
    Thanks



    I am having some difficulties with a user control implementing
    IPostBackDataHandler when it is placed inside a datagrid.

    I have created a user control (MyUserControl.ascx) containing 1 TextBox
    that implements the IPostBackDataHandler.
    I have also created a form (WebForm1.aspx) that contains 1 datagrid of
    which the datagrid contains the above user control as specified in its
    template.

    The purpose is to dynamically create one MyUserControl for each item in
    the datasource for display and editing.

    When the program is run and text is entered into MyUserControl's
    textbox, the LoadPostData() of MyUserControl.ascx is called as
    expected. But even though LoadPostData() returns true the
    corresponding RaisePostDataChangedEvent() is not called.


    Note: if I were to simply include the MyUserControl.ascx in
    WebForm1.aspx, then both LoadPostData() and RaisePostDataChangedEvent()
    of MyUserControl.ascx are called as expected.

    Would someone give me some insight as to why this is not working ? Am
    I missing a step somewhere ?



    Attached is the bare essential code snippets to reproduce the problem.


    MyUserControl.ascx
    -----------------------------------------------------
    <%@ Control Language="c#" AutoEventWireup="false"
    Codebehind="MyUserControl.ascx.cs" Inherits="test.MyUserControl"
    TargetSchema="http://schemas.microsoft.com/intellisense/ie5"%>
    <asp:TextBox id="TextBox1" runat="server"></asp:TextBox>


    MyUserControl.ascx.cs
    -----------------------------------------------------
    public class MyUserControl : System.Web.UI.UserControl,
    IPostBackDataHandler, INamingContainer
    {
    protected System.Web.UI.WebControls.TextBox TextBox1;


    #region Web Form Designer generated code
    override protected void OnInit(EventArgs e)
    {
    //
    // CODEGEN: This call is required by the ASP.NET Web Form Designer.
    //
    InitializeComponent();
    base.OnInit(e);

    if (Page != null)
    {
    Page.RegisterRequiresPostBack(this);
    }
    }

    /// <summary>
    /// Required method for Designer support - do not modify
    /// the contents of this method with the code editor.
    /// </summary>
    private void InitializeComponent()
    {
    this.Load += new System.EventHandler(this.Page_Load);

    }
    #endregion


    public virtual bool LoadPostData(string postDataKey,
    System.Collections.Specialized.NameValueCollection postCollection)
    {
    return true;
    }

    public virtual void RaisePostDataChangedEvent()
    {
    }

    private void Page_Load(object sender, System.EventArgs e)
    {
    }
    }



    WebForm1.aspx
    ------------------------------------------------------
    <%@ Register TagPrefix="f4c" TagName="MyUserControl"
    Src="MyUserControl.ascx" %>
    <%@ Page language="c#" Codebehind="WebForm1.aspx.cs"
    AutoEventWireup="false" Inherits="test.WebForm1" %>
    ....
    <form id="Form1" method="post" runat="server">
    <asp:datagrid id="dgListing" runat="server"
    AutoGenerateColumns="False">
    <Columns>
    <asp:TemplateColumn>
    <ItemTemplate>
    <f4c:MyUserControl id="MyUserControl1"
    runat="server"></f4c:MyUserControl>
    </ItemTemplate>
    </asp:TemplateColumn>
    </Columns>
    </asp:datagrid>
    <asp:Button id="Button1" runat="server" Text="Button"></asp:Button>
    </form>


    WebForm1.aspx.cs
    ------------------------------------------------------
    public class WebForm1 : System.Web.UI.Page
    {

    ....
    private void Page_Load(object sender, System.EventArgs e)
    {
    //setup handlers
    this.Button1.Click += new System.EventHandler(this.Button1_Click);

    //setup datagrid
    dgListing.DataSource = this.CreateDataSource();
    dgListing.DataBind();
    }

    private void Button1_Click(object sender, System.EventArgs e)
    {
    }

    ICollection CreateDataSource()
    {
    DataTable dt = new DataTable();
    DataRow dr;

    dt.Columns.Add(new DataColumn("SomeColumn", typeof(Int32)));

    for (int i = 0; i < 2; i++)
    {
    dr = dt.NewRow();
    dr[0] = i;
    dt.Rows.Add(dr);
    }

    DataView dv = new DataView(dt);
    return dv;
    }
    }
     
    buzlite, Aug 11, 2006
    #1
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  2. buzlite

    buzlite Guest

    The user control is added inside the WebForm1.aspx file inside the
    column template of the datagrid control

    Thanks
     
    buzlite, Aug 12, 2006
    #2
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  3. buzlite

    buzlite Guest

    Hello All,
    Any help would be appreciated.
    Thanks



     
    buzlite, Aug 14, 2006
    #3
  4. buzlite

    buzlite Guest

    Hello Gaurav,

    I do not know the reasoning for adding a hidden field and what purpose
    that would accomplish.
    Datagrid generates MyUserControl user control, any text that is entered
    in this user control TextBox would be properly posted back to the
    server. This is true in that when MyUserControl.ascx.cs,
    LoadPostData() is called, the data can be retrieved from the input
    parameter of this method. So...this is working OK.

    The problem is, when MyUserControl.ascx.cs, LoadPostData() returns a
    value of 'true', RaisePostDataChangedEvent() is never invoked. In the
    MyUserControl.ascx.cs code snippet, I hardcoded a return of 'true'.
    Even then, RaisePostDataChangedEvent() is never invoked. This is the
    main problem that I am experiencing.

    Any insights ?

    Thanks


     
    buzlite, Aug 14, 2006
    #4
  5. buzlite

    buzlite001 Guest

    Hello Gaurav,

    Thanks for you attempt but it was not answering the initial problem.

    The initial problem was that the MyUserControl is embedded in a
    Datagrid control. Please checkout the file WebForm1.aspx in my previous
    email.

    With the configuration as shown in WebForm1.aspx, the user control is
    embedded in a datagrid control. When this file is executed and text is
    entered into the user control textbox, LoadPostData() of the user
    control is invoked. But even though LoadPostData() returns 'true', the
    corresponding RaisePostDataChangedEvent() is not called. This is the
    problem I am trying to find a solution to.

    By the way, I am using Visual Studio.NET 2003 with .NET framework 1.1.
    I think you are using Visual Studio.NET 2005 with .NET framework 2.0.
    Nevertheless, I do not know if this would affect the result. I would
    be curious though.

    Thanks


     
    buzlite001, Aug 15, 2006
    #5
  6. buzlite

    buzlite Guest

    Yes I have. I had to adapt your code to Visual Studio.NET 2003 though.
    It was exhibiting the same problem in that RaisePostDataChangedEvent()
    of the user control is not being called even when LoadPostData() of the
    user control returns 'true' back to the framework.

    Hope you have better luck.



     
    buzlite, Aug 16, 2006
    #6
  7. hi, the reason your postDataChanged event never makes it is because you have
    the user control nested in a datagrid. The datagrid control internally
    overrides the onBubbleEvent, and only raises command event, to which you can
    get to using the ItemCommand method exposed by the datagrid, giving you a
    central location to branch out. Only command events are raised and exposed
    via the ItemCommand method because command events can contain CommandName
    and CommandArgument properties which can futher be used to distinguish
    between who fired what event(stored by you in CommandName property), and
    also a chance to pass some custom data(via the commandArgument property) .

    In your case you want to fire a non command event, so
    1. Nothing will be fired in the DataGrids ItemCommand, and
    2. the event is supressed since onbubble event is overridden by the datagrid
    and no action is provided to handle any events raised other than command
    events.

    To work around, you can expose a textchanged event by your usercontrol
    class, and attach the event declaratively as the following code snippet,
    note OnTextChanged="WebUserControl11_TextChanged".

    Another mistake i have seen in your code is that you rebind your datagrid in
    page_load, whether its postback or not. If you do this, then the datagrid
    will rebind, rebuilding everything and you lose state. This also will
    execute before you user control gets a chance to inspect postdata changes.
    So only rebind the grid, if its not a postback scenario.

    Regards,
    Alessandro Zifiglio
    http://www.AsyncUI.net


    <asp:DataGrid id="DataGrid1" runat="server" EnableViewState="True"
    AutoGenerateColumns="False">
    <Columns>
    <asp:TemplateColumn HeaderText="Template Column1">
    <ItemTemplate>
    <uc1:WebUserControl1 id="WebUserControl11"
    OnTextChanged="WebUserControl11_TextChanged"
    runat="server"></uc1:WebUserControl1>
    </ItemTemplate>
    </asp:TemplateColumn>
    </Columns>
    </asp:DataGrid>


    public void WebUserControl11_TextChanged(object sender, System.EventArgs e)
    {
    string text1 = (string)((WebUserControl1)sender).Text;
    Response.Write(text1);
    }


    In your user control class you would be doing this to expose the public
    event :
    ----------------------------------------------------------------------------------


    public class WebUserControl1 : System.Web.UI.UserControl,
    System.Web.UI.IPostBackDataHandler, System.Web.UI.INamingContainer
    {
    protected System.Web.UI.WebControls.TextBox TextBox1;

    public event EventHandler TextChanged;
    public string Text
    {
    get
    {
    return this.TextBox1.Text;
    }

    set
    {
    this.TextBox1.Text = value;
    }
    }

    // return true only if the text has changed
    // otherwise false.
    public virtual bool LoadPostData(string postDataKey, NameValueCollection
    postCollection)
    {

    String presentValue = Text;
    String postedValue = postCollection[postDataKey];
    if (postedValue == null)
    postedValue = string.Empty;
    if (!presentValue.Equals(postedValue))
    {
    return true;
    }
    return false;
    }

    public virtual void RaisePostDataChangedEvent()
    {
    OnTextChanged(EventArgs.Empty);
    }

    protected virtual void OnTextChanged(EventArgs e)
    {
    if (TextChanged != null)
    TextChanged(this,e);
    }

    override protected void OnInit(EventArgs e)
    {
    InitializeComponent();
    base.OnInit(e);

    if (Page != null)
    {
    Page.RegisterRequiresPostBack(this);
    }

    }


     
    Alessandro Zifiglio, Aug 17, 2006
    #7
  8. buzlite

    buzlite Guest

    Thanks for the help Alessandro. Your explanation was very insightful.
    Your code snippet worked like a charm.

    Gaurav, if you're reading this posting, thanks to you too for helping.

    Have a great day All.



     
    buzlite, Aug 18, 2006
    #8
  9. your welcome.

    Regards,
    Alessandro Zifiglio
    http://www.AsyncUI.net

     
    Alessandro Zifiglio, Aug 19, 2006
    #9
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