Question

My view page contains a search-by-example form with the following checkbox code:

<td> <label for='HasProcessErrors'>Has Errors:</label> <%= Html.CheckBox('HasProcessErrors', crit.HasProcessErrors) %> </td> 

The crit object HasProcessErrors property is a boolean whose initial value is false. When I view the source of my rendered page, I see that the helper has generated the following HTML:

<td> <label for='HasProcessErrors'>Has Errors:</label> <input id='HasProcessErrors' name='HasProcessErrors' type='checkbox' value='true' /><input name='HasProcessErrors' type='hidden' value='false' /> </td> 

Have I used the CheckBox helper incorrectly here, or is something odd going on? It seems like it should generate an input of type checkbox with checked = ”.

Thanks for any ideas.

Answer 1

Yes this is correct.

The semantics of a checkbox are a little bit different from what you may think; instead of posting a value indicating its checked/unchecked state, a checked checkbox posts whatever is in its ‘value’ attribute, and an unchecked checkbox posts nothing.

As there is also a hidden field with the same name, if you debug your form submit, you will find a checked checkbox has the value ‘true,false’ whilst an unchecked box has the value ‘false’

You can determine if a checkbox is checked by testing if it contains ‘true’.

 public ActionResult(FormCollection form) {    bool checked = form['checkbox_id'].ToString().Contains('true'); }