How to dynamically create and add textbox to a placeholder using AJAX?
<p>I'm trying to create text box dynamically. so I cal  it through the AJAX function. </p>

<p>This is my code:</p>

<p><strong>Ajax function</strong></p>

<pre><code>function ChangedAdults(noofAdults) {
    alert(noofAdults.value);
    $.ajax({

        type: 'POST',
        dataType: 'json',
        url: "/FlightBooking.aspx/Adults",

        data: "{noOfAdults:'" + noofAdults.value +  "'}",
        contentType: "application/json; charset=utf-8",
        success: function (result) {
                     $("#AdultsList").html(result.d);
                 },
        error: function (xhr, ajaxOptions, thrownError) {
                   alert(xhr.status);
                   alert(thrownError);
               }
    });
}
</code></pre>

<p><strong>code behind</strong></p>

<pre><code>[WebMethod]
public static string Adults(int noOfAdults)
{
    FlightBooking obj = new FlightBooking();
    obj.CreateAdultsList(noOfAdults);          

    string test= "";
    return test.ToString();
}
private void CreateAdultsList(int noOfAdults)
{
    int n = noOfAdults;
    for (int i = 0; i &lt; n; i++)
    {
        TextBox MyTextBox = new TextBox();                      
        MyTextBox.ID = "tb" + "" + i;    
        AdultsListPlaceholder.Controls.Add(MyTextBox); //error coming here
        AdultsListPlaceholder.Controls.Add(new LiteralControl("&lt;br /&gt;"));
    }
}
</code></pre>

<p>But I receive an error:</p>

<blockquote>
  <p>Object reference not set to an instance of an object </p>
</blockquote>

<p>What could cause this problem?</p>
