getting TextBox Text before post back

Question

I'm building a user control that is a multiple text box generator. it gives you the ability to create as much textboxs as you need..

My problem is that every time i'm using the btnAdd to add a new TextBox, the .Net is sending a post back to the server - which removes all the text inside the current text boxes..

Is there a way that i can catch the text in the textbox before the callback in order to re-render the user control with the text inside ?

HTML part:

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="MultipleTextBox.ascx.cs"
    Inherits="MultipleTextBox" %>
<asp:ScriptManager runat="server" ID="scriptManager">
</asp:ScriptManager>
<asp:UpdatePanel ID="updatePanel" runat="server">
    <contenttemplate>
<div id="container" runat="server">
</div>

<asp:Button runat="server" Text="+" ID="btnAdd" OnClick="btnAdd_Click"></asp:Button>
<asp:Button runat="server" Text="-" ID="btnRemove" onclick="btnRemove_Click"></asp:Button>

</contenttemplate>
</asp:UpdatePanel>

Code:

public partial class MultipleTextBox : System.Web.UI.UserControl
{
    /// <summary>
    /// The Session key for text box list
    /// </summary>
    private readonly string SESSION_TEXTBOX_LIST = "textboxList";

    /// <summary>
    /// The Session key for MultipleTextBox name
    /// </summary>
    private readonly string SESSION_NAME = "multipleTextBoxName";

    /// <summary>
    /// The List of TextBox instances
    /// </summary>
    private List<TextBox> textBoxList;

    /// <summary>
    /// The basic name of this multiple text box
    /// </summary>
    private string name;

    protected void Page_Load(object sender, EventArgs e)
    {                
        //disable the validation using does buttons
        btnAdd.CausesValidation = false;
        btnRemove.CausesValidation = false;
        //if it's not a post back - intialize the page
        if (!IsPostBack)
        {
            Session[SESSION_TEXTBOX_LIST] = null;
            Session[SESSION_NAME] = null;
            textBoxList = new List<TextBox>();
            Session[SESSION_TEXTBOX_LIST] = textBoxList;
            btnRemove.Visible = false;
            return;
        }
        //get the name
        if (Session[SESSION_NAME] != null)
            name = (string)Session[SESSION_NAME];
        //get the text box list
        if (Session[SESSION_TEXTBOX_LIST] != null)
            textBoxList = (List<TextBox>)Session[SESSION_TEXTBOX_LIST];
    }

    protected void btnAdd_Click(object sender, EventArgs e)
    {
        //add a new text box to the text box list
        textBoxList.Add(createTextBox());
        //show the text boxes
        ShowTextboxes(false);
        if (textBoxList.Count > 0)
            btnRemove.Visible = true;
    }

    protected void btnRemove_Click(object sender, EventArgs e)
    {
        //show the text boxes
        ShowTextboxes(true);
        //set the visibility of the remove button
        if (textBoxList.Count == 0)
            btnRemove.Visible = false;
    }

    /// <summary>
    /// Set the buttons for this control
    /// </summary>
    private void setButtons()
    {
        //set the visibility of the remove button
        if (textBoxList.Count == 0)
            btnRemove.Visible = false;
        else
            btnRemove.Visible = true;
    }

    /// <summary>
    /// Create a new TextBox
    /// </summary>
    /// <returns>a new TextBox with the right name attribute</returns>
    private TextBox createTextBox()
    {
        TextBox textbox = new TextBox();
        textbox.Attributes["name"] = name + "_" + (textBoxList.Count + 1);
        textbox.ID = name + "_" + (textBoxList.Count + 1);
        return textbox;
    }

    /// <summary>
    /// Show the TextBox instances
    /// </summary>
    /// <param name="isRemoveLast">true - use after clicking the remove button - will remove the last TextBox element. false - will show the whole TextBox list</param>
    private void ShowTextboxes(bool isRemoveLast)
    {
        if (textBoxList == null || name == null)
            return;
        //if remove the last element - remove it
        if (isRemoveLast)
            textBoxList.RemoveAt(textBoxList.Count - 1);
        //add each text box to the container
        foreach (TextBox textBox in textBoxList)
        {
            //RequiredFieldValidator validator = new RequiredFieldValidator();
            //validator.ErrorMessage = "*required";
            //validator.ControlToValidate = textBox.ID;
            container.Controls.Add(textBox);
            //container.Controls.Add(validator);
            container.Controls.Add(new LiteralControl("<br/>"));
        }
    }

    /// <summary>
    /// Get or set the basic name of thei MultipleTextBox
    /// </summary>
    public string Name
    {
        get
        {
            return this.name;
        }
        set
        {
            this.name = value;
        }
    }
}

P.S Would love for answer with pure C# and .Net. not JavaScript if possible..

Answer 1

You should be able to get the textbox values from Request.Form. Try changing your ShowTextboxes method to

private void ShowTextboxes(bool isRemoveLast)
{
    if (textBoxList == null || name == null)
        return;
    //if remove the last element - remove it
    if (isRemoveLast)
        textBoxList.RemoveAt(textBoxList.Count - 1);
    //add each text box to the container
    foreach (TextBox textBox in textBoxList)
    {
        // Populate value
        textBox.Text = Request.Form[textBox.Name]

        //RequiredFieldValidator validator = new RequiredFieldValidator();
        //validator.ErrorMessage = "*required";
        //validator.ControlToValidate = textBox.ID;
        container.Controls.Add(textBox);
        //container.Controls.Add(validator);
        container.Controls.Add(new LiteralControl("<br/>"));
    }
}