Dynamic Forms in Spring

Question

I am trying to make a dynamic form using Spring forms. Basically, the form gets a title of learning activity and then there's the a button below it that says, "Add one more Learning Activity". This makes it possible for the user to add one more learning activity. I want him to be able to add as much as he likes.

I haven't tried this before so obviously I encountered errors with the first solution I thought of. I really had a feeling doing what I did will generate an error but just do drive home what I am trying to do, here's the code:

<script language="javascript">
 fields = 0;
 function addInput() {
      document.getElementById('text').innerHTML += "<form:input path='activity[fields++].activity'/><br />";
 }

<div id="text">
  <form:form commandName="course">
   Learning Activity 1 
   <form:input path="activity[0].activity"/>
    <input type="button" value="add activity" onclick="addInput()"/>
    <br/><br/>
   <input type="submit"/>
  </form:form>  
  <br/><br/>
 </div>

Answer 1

You can't use <form:input> within the javascript because is a jsp tag that runs on the server-side.

However, there's nothing magical about how an HTML input gets bound to a field in the Spring command object; it's just based on the name. So in your javascript, add a new <input type="text" name="activity[1].activity"> (for example -- obviously you'll increment the index).

Another option I've used for more complicated controls is to grab the HTML of the existing control (which was created using the Spring form:input tag) and clone it, replacing the indexes with the incremented number. This gets a lot easier if you use jQuery.

EDITED TO ADD: One issue that may cause you problems: you're appending your new input box to the end of your outer div ("text"), which means it's not inside the form tags. That won't work.