HTML/CSS: what's a better option for layout of a tree of nested elements than nested tables?

Question

Ok, I have a set of checkboxes for selecting criteria. For argument's sake, we'll say the data looks like this:

[] Vehicles
   [] Unpowered
      [] Bicycle
      [] Skateboard
   [] Powered
      [] Two-wheeled
         [] Motorcycle
         [] Scooter
      [] Four-wheeled
etc

The []s represent checkboxes.

Ignoring the obviously contrived nature of this example, the idea is this:

• To start with, only the Vehicle checkbox is visible;
• If the user clicks on the Vehicle checkbox is opsn up the next level (Powered, Unpowered);
• If the user selects Powered it opens up the next level (Two-wheeled, Four-wheeled);
• If the user then unchecks Powered, that level disappears.

Now this is relatively easy to set up with onclick's toggling the display CSS attribute between block and none.

This is currently structured on the page as:

<table>
<tr>
  <td><input type="checkbox" onclick="toggle('__Vehicles');"></td>
  <td>Vehicles
    <table id="__Vehicles">
    <tr>
      <td><input type="checkbox"></td>
      <td>Unpowered
etc

I should point out before someone asks: the reason the checkbox was put in table cell was to control formatting. It made it easy to effectively indent since everything in the next table cell would line up.

It all works fine but the table nesting gets pretty deep. I keep thinking there has to be a better way than this. It has to be able to be easily built dynamically and have good cross-browser support for formatting of the "tree".

I should also mention that jQuery is available. I'm using it for other things.

Suggestions?

Edit: Yes the checkbox styling is important as a couple of comments have noted. Also, I have posted a solution to this, based on the responses I've gotten, as an answer below (too big to add here), just for those curious to see an example.

Answer 1

Tables are for tabular data. Use nested lists instead and CSS for formatting.

---

If you're looking for a complete solution, here's one using pure CSS for modern browsers and JavaScript for IE:

<style>
ul.tree, ul.tree ul {
    position: relative;
    list-style: none;
    margin: 0 0 0 20px;
    padding: 0;
}
ul.tree input {
    position: absolute;
    margin-left: -20px;
}
ul.tree ul {
    display: none;
}
ul.tree input:checked ~ ul {
    display: block;
}
ul.tree label:hover {
    text-decoration: underline;
}
</style>
<ul class="tree">
  <li>
    <input type="checkbox" id="option1">
    <label for="option1">Option 1</label>
    <ul>
      <li>
       <input type="checkbox" id="option1a">
       <label for="option1a">Option 1 Sub Option A</label>
      </li>
      <li>
       <input type="checkbox" id="option1b">
       <label for="option1b">Option 1 Sub Option B</label>
      </li>
    </ul>
  </li>
  <li>
   <input type="checkbox" id="option2">
   <label for="option2">Option 2</label>
  </li>
</ul>
<!--[if lte IE 7]>
<script>
var tree = document.getElementsByTagName('ul')[0];
tree.attachEvent('onclick', function() {
    var src = event.srcElement;

    if(src.nodeName.toLowerCase() === 'label')
     var box = document.getElementById(src.htmlFor);
    else if(src.nodeName.toLowerCase() === 'input')
     var box = src;
    else return;

    for(var current = src.nextSibling;
     current && current.nodeName.toLowerCase() !== 'ul';
     current = current.nextSibling);

    if(current)
     current.style.display = box.checked ? 'block' : 'none';
});
</script>
<![endif]-->

Assumes that a checkbox is not wider that 20px.

Answer 2

Nested unordered lists are best practice for this sort of thing.

<ul>
   <li>Item 1</li>
   <li>Item 2
      <ul>
         <li>Sub Item 1</li>
         <li>Sub Item 2</li>
         <li>Sub Item 3</li>
      </ul>
   </li>
   <li>Item 3</li>
   <li>Item 4
      <ul>
         <li>Sub Item 1</li>
         <li>Sub Item 2</li>
         <li>Sub Item 3</li>
      </ul>
   </li>
</ul>

Answer 3

<ul>
    <li><input type="checkbox" />Vehicles <ul>
        <li><input type="checkbox" />Unpowered</li>
        <li><input type="checkbox" />Bicycle</li>
        <li><input type="checkbox" />Skateboard</li>
    </ul></li>
    <li><input type="checkbox" />Powered <ul>
        <li><input type="checkbox" />Two-wheeled <ul>
            <li><input type="checkbox" />Motorcycle</li>
            <li><input type="checkbox" />Scooter</li>
        </ul></li>
        <li><input type="checkbox" />Four-wheeled</li>
     </ul></li>
</ul>

Edit: a little css & js to show & hide nested elements (no checkboxes)

li.opened ul {
display: block;
}

li.closed ul {
    display: none;
}

and js...

$(document).ready(function() {

$('li input:checkbox').click(function () {
    $(this).parent().toggleClass('opened');
 $(this).parent().toggleClass('closed');
});

$('li').addClass('closed');
});

edit, again, because Sparr wants some better styles (assuming that the checkboxes have a style of "checkbox"

li input.checkbox { /* input:checkbox is not 100% compatible */
    width: 6px;
    margin: 0 2px;
    /* This makes 10px be the total "width" ofh the checkbox */
}

ul {
    margin: 0 0 0 10px; /* Or whatever your total checkbox width is */
    padding: 0;
}

li {
    padding: 0;
}

Answer 4

You could do this:

<ul>
  <li>
    <input type="checkbox" /> Option 1
    <ul>
      <li><input type="checkbox" /> Option 1 Sub Option A</li>
    </ul>
  </li>
</ul>

You'd then set the padding/margin of the UL's to 0 and 0. Then set the padding-left of the LI's to 10px.

ul {
  margin:0;
  padding:0;
}

li {
  margin:0;
  padding:0 0 0 20px; /* Each nested li will be padded incrementally */
}

For the javascript, attach an event to each checkbox that determines whether the sibling UL (if any exists) should be visible. If the box is checked, show it, else, hide it.

Answer 5

when creating cb's give them a css class depending on the level

<input class="LevelXcb" type="checkbox" />

CSS:

.Level0cb{left:4px;}
.Level1cb{left:16px;}
.Level2cb{left:28px;}

if "left" does not work, try setting "margin-left".

Answer 6

I have to chime in to suggest that you extract the javascript out from your markup, in addition to the suggestions above. Using a library such as lowpro (a favorite of mine), you can create 1 object to handle your nested checkbox behavior, and have it automatically applied, unobtrusively. Packaging up your code like this makes your markup easier to maintain, and your code easier and quicker to write, more powerful, and more easily maintained.

Answer 7

I know this isn't much related to the question, so pls don't up vote is just a sugestion.

In this example from davethegr8:

<ul>
    <li>Vehicles <ul>
        <li>Unpowered</li>
        <li>Bicycle</li>
        <li>Skateboard</li>
    </ul></li>
    <li>Powered <ul>
        <li>Two-wheeled <ul>
            <li>Motorcycle</li>
            <li>Scooter</li>
        </ul></li>
        <li>Four-wheeled</li>
     </ul></li>
</ul>

If you give each step a class, you can use jquery to make some cool drop down efects with on click:

Like

$("li.Two-wheeled").click(function(event){
   $("div.main_wrapper ul.Moto_or_scooter:hidden").slideDown("slow");
}

Just a small sugestion though :)

Answer 8

While the jQuery plugin mcDropdown approaches the nested list problem in a different way (no checkboxes), it may be suitable for your needs.

Answer 9

Wanna see some deep jQuery magic?

<ul class="tree">
  <li><input type="checkbox" name="Vehicles" checked>Vehicles
    <ul>
      <li<input type="checkbox" name="Unpowered">Unpowered
        <ul>
          <li><input type="checkbox" name="Bicycle">Bicycle</li>
          <li><input type="checkbox" name="Skateboard">Skateboard</li>
        </ul>
      </li>
      <li><input type="checkbox" name="Powered" checked>Powered
        <ul>
          <li><input type="checkbox" name="Two-wheeled">Two-wheeled
            <ul>
              <li><input type="checkbox" name="Motorcycle" checked>Motorcycle</li>
              <li><input type="checkbox" name="Scooter">Scooter</li>
            </ul>
          </li>
          <li><input type="checkbox" name="Two-Wheeled">Four-wheeled</li>
        </ul>
    </ul>
  </li>
</ul>

Note: the only decoration here is the tree class.

ul.tree {
    list-style-type: none;
    margin: 0 0 0 -22px;
    padding: 0;
}

ul.tree ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
}

ul.tree input {
    margin-right: 6px;
}

ul.tree li {
    padding: 0 0 0 22px;
    margin: 1px;
}

.closed ul {
    display: none;
}

and the magic:

$(function() {
    $("ul.tree li:has(ul) > :checkbox").click(function() {
        jQuery(this).parent().toggleClass('closed');
    }).not(":checked").parent().addClass("closed");
});

That turns the entire thing into a working opening and closing tree as you click on checkboxes. Awesome.

Thanks to davethegr8, Jonathon Sampson and others for advice.

Answer 10

If the width of the checkboxes is still an issue (after all previous answers...) you can either:

• Put all checkboxes in a fixed with box so you know exactly where the text is beginning (and the next level checkbox)
• Use some jquery calculations to get the width and set the margins of the other elements dynamically (seems a bit much though...)

Using the suggested nested list structure obviously.