ASP.NET AJAX Toolkit - CalendarExtender is reset on Postback

Question

I have an ASP.NET page that has two input elements:

1. A TextBox that is ReadOnly. This TextBox is the TargetControl of a CalendarExtender
2. A DropDownList with AutoPostBack=true

Here is the code:

<table border="0" cellpadding="0" cellspacing="0">
  <tr><td colspan="2">Date:</td></tr>
  <tr><td colspan="2">
    <asp:TextBox ID="dateTextBox" runat="server" ReadOnly="true" />
    <ajax:CalendarExtender ID="datePicker" runat="server" Format="MM/dd/yyyy" OnLoad="datePicker_Load" TargetControlID="dateTextBox" />
  </td></tr>

  <tr><td colspan="2">Select an Option:</td></tr>
  <tr>
    <td>Name:&nbsp;</td>
    <td><asp:DropDownList ID="optionsDropDownList" runat="server" AutoPostBack="true"  
      OnLoad="optionsDropDownList_Load" 
      OnSelectedIndexChanged="optionsDropDownList_SelectedIndexChanged" 
      DataTextField="Name" DataValueField="ID" />
  </td></tr>

  <tr><td><asp:Button ID="saveButton" runat="server" Text="Save" OnClick="saveButton_Click" /></td></tr>
</table>

When the DropDownList posts back, the date selected by the user with the datePicker is reset to the current date. In addition, if I look at the Text property of dateTextBox, it is equal to string.Empty.

How do I preserve the date that the user selected on a PostBack?

Answer 1

Certainly you must do as others have already suggested: set readonly field dynamically rather than in markup, and make sure you are not accidentally resetting the value in Page_Load() during postbacks...

...but you must also do the following inside Page_Load(), because the CalendarExtender object has an internal copy of the date that must be forcibly changed:

if (IsPostBack)  // do this ONLY during postbacks
{
    if (Request[txtDate.UniqueID] != null)
    {
        if (Request[txtDate.UniqueID].Length > 0)
        {
            txtDate.Text = Request[txtDate.UniqueID];
            txtDateExtender.SelectedDate = DateTime.Parse(Request[txtDate.UniqueID]);
        }
    }
}

Answer 2

The fact that the text box is read only appears to be causing this problem. I duplicated your problem using no code in any of the bound events, and the date still disappeared. However, when I changed the text box to ReadOnly=False, it worked fine. Do you need to have the textbox be read only, or can you disable it or validate the date being entered?

EDIT: OK, I have an answer for you. According to this forum question, read only controls are not posted back to the server. So, when you do a postback you will lose the value in a read only control. You will need to not make the control read only.

Answer 3

protected void Page_Load(object sender, EventArgs e)
{
    txt_sdate.Text = Request[txt_sdate.UniqueID];
}

Answer 4

If you want the textbox contents remembered after the postback and still keep it as readonly control, then you have to remove the readonly attribute from the markup, and add this in the codebehind pageload:

protected void Page_Load(object sender, EventArgs e){
    TextBox1.Attributes.Add("readonly", "readonly");
    // ...
}