Question

In order to get my EF4 EntityCollection to bind with check box values, I have to manually create the check boxes in a loop like so:

<p>
    <%: Html.Label("Platforms") %><br />
    <% for(var i = 0; i < Model.AllPlatforms.Count; ++i)
       { %>
           <%: Model.AllPlatforms[i].Platform.Name %> <input type="checkbox" name="PlatformIDs" value="<%: Model.AllPlatforms[i].Platform.PlatformID %>" /><br />
    <% } %>
</p>

It works, but it doesn’t automatically populate the group of check boxes with existing values when I’m editing a model entity. Can I fudge it with something like?

<p>
    <%: Html.Label("Platforms") %><br />
    <% for(var i = 0; i < Model.AllPlatforms.Count; ++i)
       { %>
           <%: Model.AllPlatforms[i].Platform.Name %> <input type="checkbox" name="PlatformIDs" value="<%: Model.AllPlatforms[i].Platform.PlatformID %>" checked=<%: Model.GameData.Platforms.Any(p => PlatformID == i) ? "true" : "false" %> /><br />
    <% } %>
</p>

I figure there has to be something along those lines which will work, and am just wondering if I’m on the right track.

EDIT: I’m purposely staying away from MVC’s check box HTML helper methods as they’re too inflexible for my needs. My check boxes use integers as their values by design.

Answer 1

Close. You’ll actually want to modify your server-side code so that the “checked” attribute is not emitted at all unless you want the checkbox to be checked.

checked="true"

or

checked="false"

are technically both invalid HTML. Source.

If you want a checked checkbox, you want to emit:

checked="checked"

Any value in the quotes will actually check the box (including checked=”false”), but checked=”checked” is considered proper.
So, updating your code, just tweak the ternary operator to use checked=’checked’ or nothing at all.

<%: Model.AllPlatforms[i].Platform.Name %> <input type="checkbox" name="PlatformIDs" value="<%: Model.AllPlatforms[i].Platform.PlatformID %>" <%: Model.GameData.Platforms.Any(p => p.PlatformID == i) ? "checked='checked'" : "" %> /><br />