title: How do I make an ASP.NET WebForms user control refresh itself when the selected value of an input field is changed?
body: <p>I have an input field:</p>
  <pre><code>&lt;input type=&quot;text&quot; id=&quot;StartDate&quot; /&gt;
  </code></pre>
  <p>And a user control on the same page:</p>
  <pre><code>&lt;FCMS:ContactTypesChecklist ID=&quot;ContactTypesChecklist&quot; runat=&quot;server&quot; /&gt;
  </code></pre>
  <p>Here is the markup for my user control:</p>
  <pre><code>&lt;%@ Control Language=&quot;vb&quot; AutoEventWireup=&quot;false&quot; CodeBehind=&quot;ContactTypesChecklist.ascx.vb&quot; Inherits=&quot;FCMS.ContactTypesChecklist&quot; %&gt;
  
  &lt;%@ Import Namespace=&quot;FCMSDBTools&quot; %&gt;
  &lt;%@ Import Namespace=&quot;System.Data&quot; %&gt;
  
  &lt;%
      ' TODO: put these in a nice table or something?    
      For Each dr As DataRow In DBFunctions.CurrentClientCareVisitationContactTypes.Rows
          ' TODO: filter contact types by start date specified
  %&gt;
          &lt;input type=&quot;checkbox&quot; id=&quot;ContactTypes&lt;% =dr(&quot;ClientCareVisitationContactTypeLUID&quot;) %&gt;&quot; name=&quot;ContactTypes&quot; value=&quot;&lt;% =dr(&quot;ClientCareVisitationContactTypeLUID&quot;) %&gt;&quot; /&gt;
          &lt;label for=&quot;ContactTypes&lt;% =dr(&quot;ClientCareVisitationContactTypeLUID&quot;) %&gt;&quot;&gt;&lt;% =dr(&quot;ScreenDescription&quot;)%&gt;&lt;/label&gt;
  &lt;%
      Next
  %&gt;
  </code></pre>
  <p>My problem is, I want to refresh the user control when the text entered in the StartDate input field is changed, because the list of available contact types in this system varies by date (some of them could be expired after a certain date, for instance). I haven't actually added the code to filter by date to the user control yet, but how would I make it refresh when the date field is changed? I'm pretty sure this would involve AJAX, but I'm a bit fuzzy on how all that works, and if putting the markup I want to refresh inside a user control would make it easier or harder...</p>
  <p>Thanks! </p>