= Multiple Select Helper

Selecting multiple elements in a list is sometimes tricky. You may click
inadvertably on one item of the list and lost all your previous selection. You
are forced to use Ctrl (or Command) clicks to select more than one element.

Multiple Select Helper allows you to create easy to use list for multiple
selections from array, hashes, collections or trees. The list is build using
checkboxes so you can click easily and you will not lost the elements you
clicked before. As drawback you lose the use of the keyboard in the "list".

This multiple selections are very useful in many to many relationships
(+has_and_belongs_to_many+ or <tt>has_many :through</tt> with no obligatory
fields) where a "add and remove" solution will be cumbersome.

You can download this plugin at:

http://svn.ruido-blanco.net/multiple_select/trunk

You can find this information at:

http://ruido-blanco.net/blog/rails-multiple-select-helper-plugin

== Using Multiple Select Helper

There are 3 pairs of functions that you can use depending of the source of your
data:

- +multiple_select+ (and +checkboxes_for_multiple_select+): With arrays, hashes
  or your own classes (implementing first and last in them).
- +collection_multiple_select+
  (and +checkboxes_from_collection_for_multiple_select+): With arrays of classes
  using +text_method+ and +value_method+ to access the data in the instances.
- +tree_multiple_select+ (and +checkboxes_from_tree_for_multiple_select+): With
  tree-like structures (like ActiveRecord's +acts_as_tree+) using +text_method+
  and +value_method+ to access the data in the instances.

All three posibilites supports the following options in the options hash:

[+outer_class+] Specifies the class of the div that wraps all the checkboxes.
[+selected_items+] Specifies an array of items that should be selected when the
                   list renders (only in the three main methods, the other three
                   use the +selected_items+ parameter instead).
[+inner_class+] Specifies the class of the div that wraps each checkbox.
[+position+] Determines the position of the label besides the checkbox. The value
             should be <tt>:right</tt> or <tt>:left</tt>. The default is
             <tt>:right</tt>.
[+alternate+] Determines if the class of each of the checkboxes should alternate.
              The default is not alternating classes.
[+alternate_class+] Specifies the alternative class that will be used if
                    +alternate+ option is used. The alternative class will be
                    added to the +inner_class+ option if it is also specified.
                    The default alternative class is "alt".
[+initial_alternate+] Determines if the first element of the list should be the
                      alternative one or not. The default is that the first
                      element is not the alternative one.
[+disabled+] If disabled is +true+ all the checkboxes will be disabled. If
             disabled is an array only the checkboxes in the array will be
             disabled. If disabled is +false+ no checkboxes will be disabled.
             The default is +false+.

Besides the options above described the two tree methods supports also the
following options:

[+depth+] Maximum depth the tree will be trasversed. A depth of 0 will only show
          the nodes of the first level. The default is traverse all the tree.
[+child_method+] The method that will be send to the node to obtain its children.
                 This method must only return an array of the direct children of
                 the node. The default is "children" (valid for +acts_as_tree+.
                 For +acts_as_nested_set+ use "direct_children" instead).
[+level_class+] Specifies the preffix of the class that will be used in each of
                the divs that wrap each checkbox. The +level_class+ will be
                suffixed with a incresing number according the level of the
                actual checkbox. This class will be added to the +inner_class+
                and the alternative class if they are also specified.
[+initial_level+] Specifies the first level that will be used as preffix of
                  +level_class+. The default is 0.

When you want to store your list of checked options in a "habtm" relationship
you could use something like:

 # In the model
 class Person < ActiveRecord::Base
   has_and_belongs_to_many :fruits
 end
 
 # In the view
 <%=
   collection_multiple_select(
     'fruits', Fruit.find(:all), :id, :name, :selected_items => @fruits
   )
 %>
 
 # In the controller
 @fruits = (params[:fruits] or []).collect {|item| item.to_i}
 @person.fruit_ids = @fruits

And you will have all the fruits you have selected linked to the person you are
editing.

== Version history

- 20060903
  - Added disabled option.
  - The ids generated are now HTML 4.01 valid.
  - The tree version is more efficient now.
- 20060806
  - Initial release.

== Authors

- Daniel Rodríguez Troitiño (mailto:drodrigueztroitino@yahoo.es).
- Michael Schuerig (mailto:michael@schuering.de): disabled option.