Which format does ASP.NET expect when sending array with gaps?

Question

This is my HTML:

<ul id="limitations" name="limitations" class="dropdown-menu">
   <li>
      <div class="checkbox checkbox-default">
         <input type="checkbox" id="limitation-checkbox-0" value="8" name="limitations[0]" data-name="ALS ">
         <label for="limitation-checkbox-0" style="color:black">ALS </label>
      </div>
   </li>
   <li>
      <div class="checkbox checkbox-primary">
         <input type="checkbox" id="limitation-checkbox-1" value="10" name="limitations[1]" data-name="Arthrogryposis Multiplex Congenita (AMC) &amp; Amyoplasia">
         <label for="limitation-checkbox-1" style="color:black">Arthrogryposis Multiplex Congenita (AMC) &amp; Amyoplasia</label>
      </div>
   </li>
   <li>
      <div class="checkbox checkbox-success">
         <input type="checkbox" id="limitation-checkbox-2" value="2" name="limitations[2]" data-name="Cerebral Palsy (CP), (GMFS)">
         <label for="limitation-checkbox-2" style="color:black">Cerebral Palsy (CP), (GMFS)</label>
      </div>
   </li>
   <li>
      <div class="checkbox checkbox-info">
         <input type="checkbox" id="limitation-checkbox-3" value="4" name="limitations[3]" data-name="Hearing impairment deafness or hard of hearing">
         <label for="limitation-checkbox-3" style="color:black">Hearing impairment deafness or hard of hearing</label>
      </div>
   </li>
    ... MORE <li> ...
</ul>

When I post the form, the model binder for List<int> limitations works only if the checkboxes are selected from, if there is a gap in the array, all items after the gap are not binded.

For example:

Consider the first(8) and the third(10) checkboxes are checked. The value binded to List<int> limitations is [8]. Or if all the checkboxes are checked, List<int> limitations is binded witn an empty list.

I tried changing names of the checkboxes from name="limitations[0..n]" to name="limitations[]" but that caused ASP.NET to completely ignore the values.

Isn't there a standard for such things?!

I know how I can overcome this with javascript manipulation, but I really rather not going that awkward route for such a trivial case.

Using asp.net core 1.0.0 and .Net4.6.1

It should work if you change the name for all checkboxes to name="limitations". The model binder for int[] limitations or List<int> limitations will work. — tmg
– tmg, Commented Jul 20, 2016 at 6:46

Community · Accepted Answer · 2017-05-23 12:22:34Z

1

ASP.Net model binding hasn't changed this behavior between ASP.Net 4 and ASP.Net Core. The answer here is still valid.

Your naming convention is a little off. If you have multiple <input type="checkbox"...> with the same name, it should serialize automatically to the an array that ASP.Net's model binding can accommodate.

Try using name="limitations" instead of name="limitations[0]" throughout your inputs and see if that works as expected.

edited May 23, 2017 at 12:22

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answered Jul 20, 2016 at 6:56

Squiggle

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2 Comments

gdoron Over a year ago

BTW, is that the standard? I searched for hours, no one suggested doing it like that. :(

Squiggle Over a year ago

I think the answer is "it depends". I've seen other approaches in other languages/frameworks, but I believe that's how Razor generates your markup - so it's at least standard for ASP.Net.

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