reference textbox in user control from inside the same control

Question

I have a user control with a text box and a button. When I press the button, I try to read the contents using the text box's ID (from the user control's code behind) but I always get a blank result. What is the proper way to reference a control in a user control from the same user control.

I read elsewhere that I should simply use the control ID, but somehow it is not working. I must be doing something wrong and I am hoping this is a common mistake and that someone can she some light on this.

Edit:

Markup:

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="ForumPostControl.ascx.cs" Inherits="ForumPostControl" debug="true" %>

    <div id="PostDiv" runat="server">
        <table width="100%" cellpadding="0" cellspacing="0" border="0" style="border:1px solid white; border-radius:5px; margin-bottom:5px;">
            <tr>
                <td valign="top" width="52" style="text-align:center; padding:10px 0px 10px 0px; border-bottom:1px dashed #FFF;">
                    <asp:Image ID="imgReplyPoster" runat="server" />
                </td>
                <td valign="middle" style="text-align:left; padding:10px 0px 10px 0px; border-bottom:1px dashed #FFF;">
                    <asp:HyperLink ID="lnkReplyPoster" runat="server">lnkReplyPoster</asp:HyperLink><br />
                    <asp:Label ID="lblCreated" runat="server" Text="Label"></asp:Label>
                </td>
                <td style="text-align:right; padding:10px 20px 10px 0px; border-bottom:1px dashed #FFF;">
                    <asp:LinkButton ID="btnReply" runat="server" onclick="btnReply_Click">Reply</asp:LinkButton>
                    <asp:LinkButton ID="btnDelete" runat="server" OnClick="btnDelete_Click" OnClientClick="return ConfirmClick('Do you really want to delete this post?');"><img src="images/icons/trash16.png" alt="Delete" border="0" /></asp:LinkButton>
                </td>
            </tr>
            <tr>
                <td valign="top" align="justify" style="padding:10px;" colspan="3">
                    <asp:Literal ID="ltrlPostBody" runat="server"></asp:Literal>
                </td>
            </tr>
        </table>

    <asp:PlaceHolder ID="phReply" runat="server" Visible="False">
        <div align="center" style="padding:5px 10px 10px 10px;">
            <asp:HiddenField ID="hdnParentID" runat="server" />
            <table cellpadding="0" cellspacing="0" border="0">
                <tr>
                    <td>
                        <asp:TextBox ID="txtReply" runat="server"></asp:TextBox>
                    </td>
                </tr>
                <tr>
                    <td align="right" style="padding-top:20px;">
                        <asp:LinkButton ID="lnkPostReply" runat="server" OnClick="lnkPostReply_Click">Post reply</asp:LinkButton>
                    </td>
                </tr>
            </table>
        </div>
    </asp:PlaceHolder>
  </div>

Code behind for saving text to database:

protected void lnkPostReply_Click(Object sender, EventArgs e)
{
    String connectionString = (String)System.Configuration.ConfigurationManager.AppSettings["ConnectionString"];
    SqlConnection cnn = new SqlConnection(connectionString);
    SqlCommand cmd;
    String strSQL;
    cnn.Open();

    strSQL = "INSERT INTO ForumThreads (ForumID, ParentID, PostBody, Created, CreatedBy, Modified, ModifiedBy) VALUES " +
"(@ForumID, @ParentID, @PostBody, GETDATE(), @CreatedBy, GETDATE(), @CreatedBy);";
    cmd = new SqlCommand(strSQL, cnn);
    cmd.Parameters.AddWithValue("@ForumID", prvForumID);
    cmd.Parameters.AddWithValue("@ParentID", prvForumThreadID);
    cmd.Parameters.AddWithValue("@PostBody", txtReply.Text);
    cmd.Parameters.AddWithValue("@CreatedBy", CurrentMember.MemberID);
    cmd.ExecuteNonQuery();
    cmd.Dispose();
    cnn.Close();
    cnn.Dispose();

    Response.Redirect("forum_topic.aspx?TID=" + prvEncryptedTID);
}

The problem is with reading the txtReply control.

Edit #2

I am still struggling with this and experimenting stuff. Here are some finding, I hope they can help solve the mystery. I noticed that I can read properties from the text box control such as width and ID but I cannot read the text that is entered by the user. It always returns blank. If I pre set the text programmatically to, say, "Initial Text", then when I try to read the .text property, I still get "Initial Text", no matter what the user enters. It is as if the text typed the user is lost on post back.

Answer 1

As you mentioned that you are using the usercontrol inside a repeater, I would check the page's Page_Load event method to see I am not rebinding the repeater at postback:

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        Repeater1.DataSource = GetData();
        Repeater1.DataBind();
    }
}

And my Repeater1_ItemDataBound may look something like:

protected void Repeater1_ItemDataBound(object sender, RepeaterItemEventArgs e)
{
    if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem)
    {
        ForumPostControl myControl = (ForumPostControl)e.Item.FindControl("ForumPostControl1");
        myControl.MyProperty = 20;//My custom property of user control
    }
}

Now, each postback may wipe out my usercontrol's custom property. I need to make sure it persist on postback. In my ForumPostControl.ascx.cs I would store the value of this property in visestate and retrieve when needed. I should have this code in my usercontrol:

public int MyProperty 
{ 
    get
    {
        int myProperty = 0;
        if (ViewState["MyProperty"] != null)
        {
            int.TryParse(ViewState["MyProperty"].ToString(), out myProperty);
        }
        return myProperty;
    } 
    set
    {
        ViewState["MyProperty"] = value;
    }
}