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Question
Loading Postback data for a composite control
I am having trouble with postback data for a composite control. The control is esentially a texbox, but can be a label if the ReadOnly property is set to true. On postback, I can't seem to get the value of the textbox. It is really weird to me also because once the page is fully rendered, the textbox contains the posted value!! What is going on??
aspx code
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs"
<%@ Register Namespace="MyControls" TagPrefix="sgm" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtm
<html xmlns="http://www.w3.org/1
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
TextBox1
<asp:TextBox runat="server" ID="TextBox1"></asp:TextBo
<br />
TextBox2
<sgm:SgmTextBox ID="TextBox2" runat="server" />
<br />
<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_OnClick" />
</div>
</form>
</body>
</html>
==========================
aspx.cs code
using System;
using System.Web.UI;
public partial class _Default :Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
protected void Button1_OnClick(object sender, EventArgs e)
{
TextBox1.Text += "!";
TextBox2.Text += "!";
}
}
==========================
SgmTextBox.cs code in App_Code
using System;
using System.ComponentModel;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Collections.Special
namespace MyControls
{
[DefaultProperty("Text")]
[ToolboxData("<{0}:SgmText
public sealed class SgmTextBox : CompositeControl, IPostBackDataHandler
{
public SgmTextBox()
{
}
[Bindable(false)]
[Browsable(true)]
[Category("Behavior")]
[DefaultValue(false)]
[Themeable(true)]
public bool ReadOnly
{
get
{
object readOnly = ViewState["ReadOnly"];
return (readOnly != null) ? (bool)readOnly : false;
}
set
{
ViewState["ReadOnly"] = value;
}
}
[Bindable(true)]
[Browsable(true)]
[Category("Data")]
[DefaultValue("")]
[Themeable(false)]
public string Text
{
get
{
object text = ViewState["Text"];
return (text != null) ? (string)text : string.Empty;
}
set
{
ViewState["Text"] = value;
}
}
protected override void CreateChildControls()
{
Controls.Clear();
if (ReadOnly)
{
Label label = new Label();
label.EnableViewState = false;
Controls.Add(label);
}
else
{
TextBox textBox = new TextBox();
textBox.EnableViewState = false;
textBox.Height = Height;
textBox.Width = Width;
Controls.Add(textBox);
}
}
public bool LoadPostData(string postDataKey, NameValueCollection postCollection)
{
string currentText = Text;
string postedText = postCollection[postDataKey
if (!currentText.Equals(poste
{
Text = postedText;
return true;
}
return false;
}
public void RaisePostDataChangedEvent(
{
return;
}
}
}
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by: Edwin_CPosted on 2007-04-20 at 21:40:45ID: 18950805
LoadPostData only postbacks values i HTML elements such as INPUT. Since the textbox in your composite control is not persistent (not there when it is read only), it is not appropriate to use the LoadPostData to retain your value. My suggestion is that you always create a Label and a Textbox in your composite control. In the PreRender event, your hide (make Visible = false) one of them depending on the ReadOnly value. Then you don't need the ViewState to retain the Text value. Instead you can get it directly from the Textbox control. One more thing you should note is that IDs of the Label and Textbox control should be assigned to make sure they are consistent across postbacks.