.. _using_toscawidgets:


Using Existing Widgets
======================


Finding Existing Widgets
------------------------

 * Check pypi_
 * Toscawidgets provides documentation_ for some of it's
   released packages.  Some of the docs contain `Widget Browsers`_
   that allow you to play with the widget live.
 * The Toscawidgets repository_ holds some widget libraries that have not been released.
   Use them at your own risk.
   
.. _pypi: http://pypi.python.org/pypi?%3Aaction=search&term=toscawidgets&submit=search
.. _documentation: http://toscawidgets.org/documentation
.. _`Widget Browsers`: http://toscawidgets.org/documentation/tw.forms/modules/fields/forms.html
.. _repository: http://toscawidgets.org/hg

Tutorial
--------

The overall process for using a widget is:

 * Create a single instance of the widget (or compound widget), to be
   used throughout the program
 * Pass this instance from the controller to a template
 * In the template, call the widget to display it. Parameters can be
   passed at display time, and this is commonly used for the value of
   the widget.

For this tutorial we are going to create a star rating widget which
utilizes ajax to store the user response and return a request back to
the browser to update the user's view.

Before we start using our widget we need to install it.  For the time
being, this widget has not been released to pypi so we need to install
from the trunk.

::
 
 easy_install tw.rating

import the widget into your project

::

  from tw.rating import Ratings

Create the widget inside your controllers definitions.

:: 
 
  my_rating = Rating(id='my_rating', action='rating', label_text='')

Create a new controller method to share our widget

:: 
  
  @expose('genshi:myproject.templates.widget')
  def testing(self, **kw):
      tmpl_context.widget = my_rating
      return dict()

In the template, call the widget to display it.

::

  ${tmpl_context.widget(value)}

Here is what the resulting widget looks like:

.. image:: images/stars.png

Now, star widget doesn't do any good without some kind of server
interaction.  For this tutorial we are going to just simply keep track
of the average as the user's click the stars in memory.  This could be
later modified to support some sort of crafty database interaction.

First, lets initialize our "database" of star-click averages:
::
  
  sum_ratings = 0
  num_ratings = 0

Then we make a newly exposed method which shares the same name as the
"action" which is sent into the Widget.

::
  
  @expose('json')
  def rating(self, rating):
      global sum_ratings
      global num_ratings
      rating = int(rating)
      sum_ratings += rating
      num_ratings += 1
      rating = float(sum_ratings)/float(num_ratings)
      return dict(num_ratings=num_ratings, avg_rating=rating)

This method returns a json stream to the widget which is then read as
a response by the javascript on the client side.

Now, this is not a terribly interesting example until you start to
handle the response that comes back.  To do that, you just add an
"on_click" parameter to the widget definition.

::

First we modify the template to give a place to hold the data that
comes back from the server.

::

  rating = Rating(id='my_rating', 
                  action='rating', 
                  label_text='',   
                  on_click="""$('#avg_stars')[0].textContent='The average is now: '+response.avg_rating""")

The 'response' javascript variable will hold an object which is your
extracted json stream.  In this case, we are displaying the average
rating.  It is important to note that the star widget uses the jQuery
library, and the '$' operator may not work the same in other
libraries.

.. image:: images/stars_avg.png
