=============
Button Widget
=============

The button widget allows you to provide buttons whose actions are defined
using Javascript scripts. The "button" type of the "INPUT" element is
described here:

http://www.w3.org/TR/1999/REC-html401-19991224/interact/forms.html#edef-INPUT

As for all widgets, the button widget must provide the new ``IWidget``
interface:

  >>> from zope.interface.verify import verifyClass
  >>> from z3c.form import interfaces
  >>> from z3c.form.browser import button

  >>> verifyClass(interfaces.IWidget, button.ButtonWidget)
  True

The widget can be instantiated only using the request:

  >>> from z3c.form.testing import TestRequest
  >>> request = TestRequest()

  >>> widget = button.ButtonWidget(request)

Before rendering the widget, one has to set the name and id of the widget:

  >>> widget.id = 'widget.id'
  >>> widget.name = 'widget.name'

We also need to register the template for the widget:

  >>> import zope.component
  >>> from zope.pagetemplate.interfaces import IPageTemplate
  >>> from z3c.form.testing import getPath
  >>> from z3c.form.widget import WidgetTemplateFactory

  >>> zope.component.provideAdapter(
  ...     WidgetTemplateFactory(getPath('button_input.pt'), 'text/html'),
  ...     (None, None, None, None, interfaces.IButtonWidget),
  ...     IPageTemplate, name=interfaces.INPUT_MODE)

If we render the widget we get a simple input element:

  >>> print(widget.render())
  <input type="button" id="widget.id" name="widget.name"
         class="button-widget" />

Setting a value for the widget effectively changes the button label:

  >>> widget.value = 'Button'
  >>> print(widget.render())
  <input type="button" id="widget.id" name="widget.name"
         class="button-widget" value="Button" />


Let's now make sure that we can extract user entered data from a widget:

  >>> widget.request = TestRequest(form={'widget.name': 'button'})
  >>> widget.update()
  >>> widget.extract()
  'button'

If nothing is found in the request, the default is returned:

  >>> widget.request = TestRequest()
  >>> widget.update()
  >>> widget.extract()
  <NO_VALUE>