Re: IPostBackDataHandler not working properly with DataGrid

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.



Alessandro Zifiglio wrote:
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);
}

}


<buzlite@xxxxxxxxxxxx> ha scritto nel messaggio
news:1155336658.977686.265490@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
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;
}
}


.