How to make a check_box checked in rails?

问题

I made checkboxes using the following rails form helper:

<%= check_box("tag", tag.id) %>

However, I need to make some of them checked by default. The rails documentation doesn't specify how to do this. Is there a way? How?

回答1:

This has a very straightforward solution that is directly supported by check_box (at least as of rails 4, I didn't check older documentation)

<%= check_box("tag", tag.id, {checked: true}) %>

This will make the checkbox checked. Of course instead of true you will put in some logic which determines if each one is checked.

回答2:

If you need the check_box to be checked on new, and correctly filled on edit you can do:

<%= f.check_box :subscribe, checked: @event.new_record? || f.object.subscribe? %>

As I mentioned here

回答3:

The rails docs do say how to have it checked and it depends on the object. If you don't have an instance object to use with check_box, then your best option is to use the check_box_tag as mentioned. If you do, read on.

Here's the link to the docs on the check_box helper. Basically how this works is that you have to have an instance variable defined. That instance variable must have a method that returns an integer or a boolean. From the docs:

This object must be an instance object (@object) and not a local object. It’s intended that method returns an integer and if that integer is above zero, then the checkbox is checked.

For example, let's assume you have a @tag instance in your view which has an enabled method. The following snippet would cause the checkbox to be checked when enabled is true on the @tag object and unchecked when it is false. To have it enabled by default, set the enabled attribute to true in your controller. The last two variables are the values that you want to submit with the form when the check box is checked and unchecked.

<%= check_box "tag", "enabled", {}, "1", "0" %>

A lot of times, you'll see the check_box helper used with a form builder. So if form_for was used for the @tag instance, you would more than likely use this snippet:

<%= f.check_box :enabled %>

回答4:

The check_box_tag instead of check_box has a way to set that it's been checked.

回答5:

No need of writing checked: true for rails >= 4.0 Simply write

<%= check_box_tag "name", value, true %> # true or false

回答6:

Using check_box_tag you can set it to true so that it's already checked. More info here: http://api.rubyonrails.org/classes/ActionView/Helpers/FormTagHelper.html#method-i-check_box_tag

回答7:

Problem with all of these solutions is that it doesn't play well with the params hash on resubmits, so at the moment I'm using something like this,

# ApplicationHelper
def resolve_boolean_parameter resource, attribute, options = {}
  default = options.delete(:default)
  return default unless params[:utf8]

  return params[resource][attribute] == "1"
end

and then in the view:

<div><%= f.label :accepts_newsletter, "Receive Newsletters" %>
  <%= f.check_box :accepts_newsletter, :checked => resolve_boolean_parameter(:user, :accepts_newsletter, default: true)  %>
</div>

回答8:

New Function placed in your Helper

def check_if_true(item)
  ActiveModel::Type::Boolean.new.cast(item)
end

In your View

<%= check_box("test", "active", {checked: check_if_true(@test.active) , :multiple => true, :style => "margin-left: 16px;"}, "true", "false") %>

来源：https://stackoverflow.com/questions/13616554/how-to-make-a-check-box-checked-in-rails