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310 lines
13 KiB
Plaintext
310 lines
13 KiB
Plaintext
Form Media
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==========
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Rendering an attractive and easy-to-use Web form requires more than just
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HTML - it also requires CSS stylesheets, and if you want to use fancy
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"Web2.0" widgets, you may also need to include some JavaScript on each
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page. The exact combination of CSS and JavaScript that is required for
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any given page will depend upon the widgets that are in use on that page.
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This is where Django media definitions come in. Django allows you to
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associate different media files with the forms and widgets that require
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that media. For example, if you want to use a calendar to render DateFields,
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you can define a custom Calendar widget. This widget can then be associated
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with the CSS and JavaScript that is required to render the calendar. When
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the Calendar widget is used on a form, Django is able to identify the CSS and
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JavaScript files that are required, and provide the list of file names
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in a form suitable for easy inclusion on your Web page.
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.. admonition:: Media and Django Admin
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The Django Admin application defines a number of customized widgets
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for calendars, filtered selections, and so on. These widgets define
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media requirements, and the Django Admin uses the custom widgets
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in place of the Django defaults. The Admin templates will only include
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those media files that are required to render the widgets on any
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given page.
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If you like the widgets that the Django Admin application uses,
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feel free to use them in your own application! They're all stored
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in ``django.contrib.admin.widgets``.
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.. admonition:: Which JavaScript toolkit?
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Many JavaScript toolkits exist, and many of them include widgets (such
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as calendar widgets) that can be used to enhance your application.
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Django has deliberately avoided blessing any one JavaScript toolkit.
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Each toolkit has its own relative strengths and weaknesses - use
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whichever toolkit suits your requirements. Django is able to integrate
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with any JavaScript toolkit.
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Media as a static definition
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----------------------------
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The easiest way to define media is as a static definition. Using this method,
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the media declaration is an inner class. The properties of the inner class
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define the media requirements.
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Here's a simple example::
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class CalendarWidget(forms.TextInput):
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class Media:
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css = {
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'all': ('pretty.css',)
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}
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js = ('animations.js', 'actions.js')
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This code defines a ``CalendarWidget``, which will be based on ``TextInput``.
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Every time the CalendarWidget is used on a form, that form will be directed
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to include the CSS file ``pretty.css``, and the JavaScript files
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``animations.js`` and ``actions.js``.
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This static media definition is converted at runtime into a widget property
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named ``media``. The media for a CalendarWidget instance can be retrieved
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through this property::
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>>> w = CalendarWidget()
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>>> print w.media
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<link href="http://media.example.com/pretty.css" type="text/css" media="all" rel="stylesheet" />
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<script type="text/javascript" src="http://media.example.com/animations.js"></script>
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<script type="text/javascript" src="http://media.example.com/actions.js"></script>
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Here's a list of all possible ``Media`` options. There are no required options.
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``css``
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~~~~~~~
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A dictionary describing the CSS files required for various forms of output
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media.
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The values in the dictionary should be a tuple/list of file names. See
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`the section on media paths`_ for details of how to specify paths to media
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files.
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.. _the section on media paths: `Paths in media definitions`_
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The keys in the dictionary are the output media types. These are the same
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types accepted by CSS files in media declarations: 'all', 'aural', 'braille',
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'embossed', 'handheld', 'print', 'projection', 'screen', 'tty' and 'tv'. If
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you need to have different stylesheets for different media types, provide
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a list of CSS files for each output medium. The following example would
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provide two CSS options -- one for the screen, and one for print::
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class Media:
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css = {
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'screen': ('pretty.css',),
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'print': ('newspaper.css',)
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}
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If a group of CSS files are appropriate for multiple output media types,
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the dictionary key can be a comma separated list of output media types.
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In the following example, TV's and projectors will have the same media
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requirements::
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class Media:
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css = {
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'screen': ('pretty.css',),
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'tv,projector': ('lo_res.css',),
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'print': ('newspaper.css',)
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}
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If this last CSS definition were to be rendered, it would become the following HTML::
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<link href="http://media.example.com/pretty.css" type="text/css" media="screen" rel="stylesheet" />
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<link href="http://media.example.com/lo_res.css" type="text/css" media="tv,projector" rel="stylesheet" />
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<link href="http://media.example.com/newspaper.css" type="text/css" media="print" rel="stylesheet" />
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``js``
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~~~~~~
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A tuple describing the required JavaScript files. See
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`the section on media paths`_ for details of how to specify paths to media
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files.
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``extend``
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~~~~~~~~~~
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A boolean defining inheritance behavior for media declarations.
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By default, any object using a static media definition will inherit all the
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media associated with the parent widget. This occurs regardless of how the
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parent defines its media requirements. For example, if we were to extend our
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basic Calendar widget from the example above::
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class FancyCalendarWidget(CalendarWidget):
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class Media:
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css = {
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'all': ('fancy.css',)
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}
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js = ('whizbang.js',)
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>>> w = FancyCalendarWidget()
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>>> print w.media
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<link href="http://media.example.com/pretty.css" type="text/css" media="all" rel="stylesheet" />
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<link href="http://media.example.com/fancy.css" type="text/css" media="all" rel="stylesheet" />
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<script type="text/javascript" src="http://media.example.com/animations.js"></script>
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<script type="text/javascript" src="http://media.example.com/actions.js"></script>
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<script type="text/javascript" src="http://media.example.com/whizbang.js"></script>
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The FancyCalendar widget inherits all the media from it's parent widget. If
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you don't want media to be inherited in this way, add an ``extend=False``
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declaration to the media declaration::
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class FancyCalendarWidget(CalendarWidget):
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class Media:
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extend = False
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css = {
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'all': ('fancy.css',)
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}
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js = ('whizbang.js',)
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>>> w = FancyCalendarWidget()
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>>> print w.media
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<link href="http://media.example.com/fancy.css" type="text/css" media="all" rel="stylesheet" />
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<script type="text/javascript" src="http://media.example.com/whizbang.js"></script>
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If you require even more control over media inheritance, define your media
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using a `dynamic property`_. Dynamic properties give you complete control over
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which media files are inherited, and which are not.
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.. _dynamic property: `Media as a dynamic property`_
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Media as a dynamic property
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---------------------------
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If you need to perform some more sophisticated manipulation of media
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requirements, you can define the media property directly. This is done
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by defining a widget property that returns an instance of ``forms.Media``.
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The constructor for ``forms.Media`` accepts ``css`` and ``js`` keyword
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arguments in the same format as that used in a static media definition.
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For example, the static media definition for our Calendar Widget could
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also be defined in a dynamic fashion::
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class CalendarWidget(forms.TextInput):
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def _media(self):
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return forms.Media(css={'all': ('pretty.css',)},
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js=('animations.js', 'actions.js'))
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media = property(_media)
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See the section on `Media objects`_ for more details on how to construct
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return values for dynamic media properties.
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Paths in media definitions
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--------------------------
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Paths used to specify media can be either relative or absolute. If a path
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starts with '/', 'http://' or 'https://', it will be interpreted as an absolute
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path, and left as-is. All other paths will be prepended with the value of
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``settings.MEDIA_URL``. For example, if the MEDIA_URL for your site was
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``http://media.example.com/``::
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class CalendarWidget(forms.TextInput):
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class Media:
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css = {
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'all': ('/css/pretty.css',),
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}
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js = ('animations.js', 'http://othersite.com/actions.js')
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>>> w = CalendarWidget()
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>>> print w.media
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<link href="/css/pretty.css" type="text/css" media="all" rel="stylesheet" />
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<script type="text/javascript" src="http://media.example.com/animations.js"></script>
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<script type="text/javascript" src="http://othersite.com/actions.js"></script>
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Media objects
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-------------
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When you interrogate the media attribute of a widget or form, the value that
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is returned is a ``forms.Media`` object. As we have already seen, the string
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representation of a Media object is the HTML required to include media
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in the ``<head>`` block of your HTML page.
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However, Media objects have some other interesting properties.
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Media subsets
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~~~~~~~~~~~~~
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If you only want media of a particular type, you can use the subscript operator
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to filter out a medium of interest. For example::
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>>> w = CalendarWidget()
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>>> print w.media
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<link href="http://media.example.com/pretty.css" type="text/css" media="all" rel="stylesheet" />
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<script type="text/javascript" src="http://media.example.com/animations.js"></script>
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<script type="text/javascript" src="http://media.example.com/actions.js"></script>
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>>> print w.media['css']
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<link href="http://media.example.com/pretty.css" type="text/css" media="all" rel="stylesheet" />
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When you use the subscript operator, the value that is returned is a new
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Media object -- but one that only contains the media of interest.
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Combining media objects
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~~~~~~~~~~~~~~~~~~~~~~~
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Media objects can also be added together. When two media objects are added,
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the resulting Media object contains the union of the media from both files::
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class CalendarWidget(forms.TextInput):
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class Media:
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css = {
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'all': ('pretty.css',)
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}
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js = ('animations.js', 'actions.js')
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class OtherWidget(forms.TextInput):
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class Media:
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js = ('whizbang.js',)
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>>> w1 = CalendarWidget()
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>>> w2 = OtherWidget()
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>>> print w1.media + w2.media
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<link href="http://media.example.com/pretty.css" type="text/css" media="all" rel="stylesheet" />
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<script type="text/javascript" src="http://media.example.com/animations.js"></script>
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<script type="text/javascript" src="http://media.example.com/actions.js"></script>
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<script type="text/javascript" src="http://media.example.com/whizbang.js"></script>
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Media on Forms
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--------------
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Widgets aren't the only objects that can have media definitions -- forms
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can also define media. The rules for media definitions on forms are the
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same as the rules for widgets: declarations can be static or dynamic;
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path and inheritance rules for those declarations are exactly the same.
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Regardless of whether you define a media declaration, *all* Form objects
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have a media property. The default value for this property is the result
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of adding the media definitions for all widgets that are part of the form::
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class ContactForm(forms.Form):
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date = DateField(widget=CalendarWidget)
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name = CharField(max_length=40, widget=OtherWidget)
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>>> f = ContactForm()
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>>> f.media
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<link href="http://media.example.com/pretty.css" type="text/css" media="all" rel="stylesheet" />
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<script type="text/javascript" src="http://media.example.com/animations.js"></script>
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<script type="text/javascript" src="http://media.example.com/actions.js"></script>
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<script type="text/javascript" src="http://media.example.com/whizbang.js"></script>
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If you want to associate additional media with a form -- for example, CSS for form
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layout -- simply add a media declaration to the form::
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class ContactForm(forms.Form):
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date = DateField(widget=CalendarWidget)
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name = CharField(max_length=40, widget=OtherWidget)
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class Media:
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css = {
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'all': ('layout.css',)
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}
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>>> f = ContactForm()
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>>> f.media
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<link href="http://media.example.com/pretty.css" type="text/css" media="all" rel="stylesheet" />
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<link href="http://media.example.com/layout.css" type="text/css" media="all" rel="stylesheet" />
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<script type="text/javascript" src="http://media.example.com/animations.js"></script>
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<script type="text/javascript" src="http://media.example.com/actions.js"></script>
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<script type="text/javascript" src="http://media.example.com/whizbang.js"></script>
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