Let's start with some motivation. Using content providers allows us to insert one piece of HTML content. In most Web development, however, you are often interested in defining some sort of region and then allow developers to register content for those regions.
>>> from zope.viewlet import interfaces
As mentioned above, besides inserting snippets of HTML at places, we more frequently want to define a region in our page and allow specialized content providers to be inserted based on configuration. Those specialized content providers are known viewlets and are only available inside viewlet managers, which are just a more complex example of content providers.
Unfortunately, the Java world does not implement this layer separately. The viewlet manager is most similar to a Java "channel", but we decided against using this name, since it is very generic and not very meaningful. The viewlet has no Java counterpart, since Java does not implement content providers using a component architecture and thus does not register content providers specifically for viewlet managers, which I believe makes the Java implementation less usefull as a generic concept. In fact, the main design goal in the Java world is the implementation of reusable and sharable portlets. The scope for Zope 3 is larger, since we want to provide a generic framework for building pluggable user interfaces.
In this implementation of viewlets, those regions are just content providers called viewlet managers that manage a special type of content providers known as viewlets. Every viewlet manager handles the viewlets registered for it:
>>> class ILeftColumn(interfaces.IViewletManager): ... """Viewlet manager located in the left column."""
You can then create a viewlet manager using this interface now:
>>> from zope.viewlet import manager >>> LeftColumn = manager.ViewletManager('left', ILeftColumn)
Now we have to instantiate it:
>>> import zope.interface >>> class Content(object): ... zope.interface.implements(zope.interface.Interface) >>> content = Content()>>> from zope.publisher.browser import TestRequest >>> request = TestRequest()>>> from zope.publisher.interfaces.browser import IBrowserView >>> class View(object): ... zope.interface.implements(IBrowserView) ... def __init__(self, context, request): ... pass >>> view = View(content, request)>>> leftColumn = LeftColumn(content, request, view)
So initially nothing gets rendered:
>>> leftColumn.update() >>> leftColumn.render() u''
But now we register some viewlets for the manager
>>> import zope.component >>> from zope.publisher.interfaces.browser import IDefaultBrowserLayer>>> class WeatherBox(object): ... zope.interface.implements(interfaces.IViewlet) ... ... def __init__(self, context, request, view, manager): ... self.__parent__ = view ... ... def update(self): ... pass ... ... def render(self): ... return u'<div class="box">It is sunny today!</div>'>>> # Create a security checker for viewlets. >>> from zope.security.checker import NamesChecker, defineChecker >>> viewletChecker = NamesChecker(('update', 'render')) >>> defineChecker(WeatherBox, viewletChecker)>>> zope.component.provideAdapter( ... WeatherBox, ... (zope.interface.Interface, IDefaultBrowserLayer, ... IBrowserView, ILeftColumn), ... interfaces.IViewlet, name='weather')>>> from zope.location.interfaces import ILocation >>> class SportBox(object): ... zope.interface.implements(interfaces.IViewlet, ... ILocation) ... ... def __init__(self, context, request, view, manager): ... self.__parent__ = view ... ... def update(self): ... pass ... ... def render(self): ... return u'<div class="box">Patriots (23) : Steelers (7)</div>'>>> defineChecker(SportBox, viewletChecker)>>> zope.component.provideAdapter( ... SportBox, ... (zope.interface.Interface, IDefaultBrowserLayer, ... IBrowserView, ILeftColumn), ... interfaces.IViewlet, name='sport')
and thus the left column is filled. Note that also events get fired before viewlets are updated. We register a simple handler to demonstrate this behaviour.
>>> from zope.contentprovider.interfaces import IBeforeUpdateEvent >>> events = [] >>> def handler(ev): ... events.append(ev) >>> zope.component.provideHandler(handler, (IBeforeUpdateEvent,)) >>> leftColumn.update() >>> [(ev, ev.object.__class__.__name__) for ev in events] [(<zope.contentprovider.interfaces.BeforeUpdateEvent...>, 'SportBox'), (<zope.contentprovider.interfaces.BeforeUpdateEvent...>, 'WeatherBox')]>>> print leftColumn.render() <div class="box">Patriots (23) : Steelers (7)</div> <div class="box">It is sunny today!</div>
But this is of course pretty lame, since there is no way of specifying how the viewlets are put together. But we have a solution. The second argument of the ViewletManager() function is a template in which we can specify how the viewlets are put together:
>>> import os, tempfile >>> temp_dir = tempfile.mkdtemp() >>> leftColTemplate = os.path.join(temp_dir, 'leftCol.pt') >>> open(leftColTemplate, 'w').write(''' ... <div class="left-column"> ... <tal:block repeat="viewlet options/viewlets" ... replace="structure viewlet/render" /> ... </div> ... ''')>>> LeftColumn = manager.ViewletManager('left', ILeftColumn, ... template=leftColTemplate) >>> leftColumn = LeftColumn(content, request, view)
TODO: Fix this silly thing; viewlets should be directly available.
As you can see, the viewlet manager provides a global options/viewlets variable that is an iterable of all the avialable viewlets in the correct order:
>>> leftColumn.update() >>> print leftColumn.render().strip() <div class="left-column"> <div class="box">Patriots (23) : Steelers (7)</div> <div class="box">It is sunny today!</div> </div>
If a viewlet provides ILocation the __name__ attribute of the viewlet is set to the name under which the viewlet is registered.
>>> [getattr(viewlet, '__name__', None) for viewlet in leftColumn.viewlets] [u'sport', None]
You can also lookup the viewlets directly for management purposes:
>>> leftColumn['weather'] <WeatherBox ...> >>> leftColumn.get('weather') <WeatherBox ...>
If the viewlet is not found, then the expected behavior is provided:
>>> leftColumn['stock'] Traceback (most recent call last): ... ComponentLookupError: No provider with name `stock` found.>>> leftColumn.get('stock') is None True
One important feature of any viewlet manager is to be able to filter and sort the viewlets it is displaying. The default viewlet manager that we have been using in the tests above, supports filtering by access availability and sorting via the viewlet's __cmp__() method (default). You can easily override this default policy by providing a base viewlet manager class.
In our case we will manage the viewlets using a global list:
>>> shown = ['weather', 'sport']
The viewlet manager base class now uses this list:
>>> class ListViewletManager(object): ... ... def filter(self, viewlets): ... viewlets = super(ListViewletManager, self).filter(viewlets) ... return [(name, viewlet) ... for name, viewlet in viewlets ... if name in shown] ... ... def sort(self, viewlets): ... viewlets = dict(viewlets) ... return [(name, viewlets[name]) for name in shown]
Let's now create a new viewlet manager:
>>> LeftColumn = manager.ViewletManager( ... 'left', ILeftColumn, bases=(ListViewletManager,), ... template=leftColTemplate) >>> leftColumn = LeftColumn(content, request, view)
So we get the weather box first and the sport box second:
>>> leftColumn.update() >>> print leftColumn.render().strip() <div class="left-column"> <div class="box">It is sunny today!</div> <div class="box">Patriots (23) : Steelers (7)</div> </div>
Now let's change the order...
>>> shown.reverse()
and the order should switch as well:
>>> leftColumn.update() >>> print leftColumn.render().strip() <div class="left-column"> <div class="box">Patriots (23) : Steelers (7)</div> <div class="box">It is sunny today!</div> </div>
Of course, we also can remove a shown viewlet:
>>> weather = shown.pop() >>> leftColumn.update() >>> print leftColumn.render().strip() <div class="left-column"> <div class="box">Patriots (23) : Steelers (7)</div> </div>
To make the creation of viewlets simpler, a set of useful base classes and helper functions are provided:
>>> from zope.viewlet import viewlet
The first class is a base class that simply defines the constructor:
>>> base = viewlet.ViewletBase('context', 'request', 'view', 'manager') >>> base.context 'context' >>> base.request 'request' >>> base.__parent__ 'view' >>> base.manager 'manager'
But a default render() method implementation is not provided:
>>> base.render() Traceback (most recent call last): ... NotImplementedError: `render` method must be implemented by subclass.
If you have already an existing class that produces the HTML content in some method, then the SimpleAttributeViewlet might be for you, since it can be used to convert any class quickly into a viewlet:
>>> class FooViewlet(viewlet.SimpleAttributeViewlet): ... __page_attribute__ = 'foo' ... ... def foo(self): ... return 'output'
The __page_attribute__ attribute provides the name of the function to call for rendering.
>>> foo = FooViewlet('context', 'request', 'view', 'manager') >>> foo.foo() 'output' >>> foo.render() 'output'
If you specify render as the attribute an error is raised to prevent infinite recursion:
>>> foo.__page_attribute__ = 'render' >>> foo.render() Traceback (most recent call last): ... AttributeError: render
The same is true if the specified attribute does not exist:
>>> foo.__page_attribute__ = 'bar' >>> foo.render() Traceback (most recent call last): ... AttributeError: 'FooViewlet' object has no attribute 'bar'
To create simple template-based viewlets you can use the SimpleViewletClass() function. This function is very similar to its view equivalent and is used by the ZCML directives to create viewlets. The result of this function call will be a fully functional viewlet class. Let's start by simply specifying a template only:
>>> template = os.path.join(temp_dir, 'demoTemplate.pt') >>> open(template, 'w').write('''<div>contents</div>''')>>> Demo = viewlet.SimpleViewletClass(template) >>> print Demo(content, request, view, manager).render() <div>contents</div>
Now let's additionally specify a class that can provide additional features:
>>> class MyViewlet(object): ... myAttribute = 8>>> Demo = viewlet.SimpleViewletClass(template, bases=(MyViewlet,)) >>> MyViewlet in Demo.__bases__ True >>> Demo(content, request, view, manager).myAttribute 8
The final important feature is the ability to pass in further attributes to the class:
>>> Demo = viewlet.SimpleViewletClass( ... template, attributes={'here': 'now', 'lucky': 3}) >>> demo = Demo(content, request, view, manager) >>> demo.here 'now' >>> demo.lucky 3
As for all views, they must provide a name that can also be passed to the function:
>>> Demo = viewlet.SimpleViewletClass(template, name='demoViewlet') >>> demo = Demo(content, request, view, manager) >>> demo.__name__ 'demoViewlet'
In addition to the the generic viewlet code above, the package comes with two viewlet base classes and helper functions for inserting CSS and Javascript links into HTML headers, since those two are so very common. I am only going to demonstrate the helper functions here, since those demonstrations will fully demonstrate the functionality of the base classes as well.
The viewlet will look up the resource it was given and tries to produce the absolute URL for it:
>>> class JSResource(object): ... def __init__(self, request): ... self.request = request ... ... def __call__(self): ... return '/@@/resource.js'>>> zope.component.provideAdapter( ... JSResource, ... (IDefaultBrowserLayer,), ... zope.interface.Interface, name='resource.js')>>> JSViewlet = viewlet.JavaScriptViewlet('resource.js') >>> print JSViewlet(content, request, view, manager).render().strip() <script type="text/javascript" src="/@@/resource.js"> </script>
There is also a javascript viewlet base class which knows how to render more then one javascript resource file:
>>> class JSSecondResource(object): ... def __init__(self, request): ... self.request = request ... ... def __call__(self): ... return '/@@/second-resource.js'>>> zope.component.provideAdapter( ... JSSecondResource, ... (IDefaultBrowserLayer,), ... zope.interface.Interface, name='second-resource.js')>>> JSBundleViewlet = viewlet.JavaScriptBundleViewlet(('resource.js', ... 'second-resource.js')) >>> print JSBundleViewlet(content, request, view, manager).render().strip() <script type="text/javascript" src="/@@/resource.js"> </script> <script type="text/javascript" src="/@@/second-resource.js"> </script>
The same works for the CSS resource viewlet:
>>> class CSSResource(object): ... def __init__(self, request): ... self.request = request ... ... def __call__(self): ... return '/@@/resource.css'>>> zope.component.provideAdapter( ... CSSResource, ... (IDefaultBrowserLayer,), ... zope.interface.Interface, name='resource.css')>>> CSSViewlet = viewlet.CSSViewlet('resource.css') >>> print CSSViewlet(content, request, view, manager).render().strip() <link type="text/css" rel="stylesheet" href="/@@/resource.css" media="all" />
You can also change the media type and the rel attribute:
>>> CSSViewlet = viewlet.CSSViewlet('resource.css', media='print', rel='css') >>> print CSSViewlet(content, request, view, manager).render().strip() <link type="text/css" rel="css" href="/@@/resource.css" media="print" />
There is also a bundle viewlet for CSS links:
>>> class CSSPrintResource(object): ... def __init__(self, request): ... self.request = request ... ... def __call__(self): ... return '/@@/print-resource.css'>>> zope.component.provideAdapter( ... CSSPrintResource, ... (IDefaultBrowserLayer,), ... zope.interface.Interface, name='print-resource.css')>>> items = [] >>> items.append({'path':'resource.css', 'rel':'stylesheet', 'media':'all'}) >>> items.append({'path':'print-resource.css', 'media':'print'}) >>> CSSBundleViewlet = viewlet.CSSBundleViewlet(items) >>> print CSSBundleViewlet(content, request, view, manager).render().strip() <link type="text/css" rel="stylesheet" href="/@@/resource.css" media="all" /> <link type="text/css" rel="stylesheet" href="/@@/print-resource.css" media="print" />
So far we have only demonstrated simple (maybe overly trivial) use cases of the viewlet system. In the following example, we are going to develop a generic contents view for files. The step is to create a file component:
>>> class IFile(zope.interface.Interface): ... data = zope.interface.Attribute('Data of file.')>>> class File(object): ... zope.interface.implements(IFile) ... def __init__(self, data=''): ... self.__name__ = '' ... self.data = data
Since we want to also provide the size of a file, here a simple implementation of the ISized interface:
>>> from zope import size >>> class FileSized(object): ... zope.interface.implements(size.interfaces.ISized) ... zope.component.adapts(IFile) ... ... def __init__(self, file): ... self.file = file ... ... def sizeForSorting(self): ... return 'byte', len(self.file.data) ... ... def sizeForDisplay(self): ... return '%i bytes' %len(self.file.data)>>> zope.component.provideAdapter(FileSized)
We also need a container to which we can add files:
>>> class Container(dict): ... def __setitem__(self, name, value): ... value.__name__ = name ... super(Container, self).__setitem__(name, value)
Here is some sample data:
>>> container = Container() >>> container['test.txt'] = File('Hello World!') >>> container['mypage.html'] = File('<html><body>Hello World!</body></html>') >>> container['data.xml'] = File('<message>Hello World!</message>')
The contents view of the container should iterate through the container and represent the files in a table:
>>> contentsTemplate = os.path.join(temp_dir, 'contents.pt') >>> open(contentsTemplate, 'w').write(''' ... <html> ... <body> ... <h1>Cotnents</h1> ... <div tal:content="structure provider:contents" /> ... </body> ... </html> ... ''')>>> from zope.app.pagetemplate.simpleviewclass import SimpleViewClass >>> Contents = SimpleViewClass(contentsTemplate, name='contents.html')
Now we have to write our own viewlet manager. In this case we cannot use the default implementation, since the viewlets will be looked up for each different item:
>>> shownColumns = []>>> class ContentsViewletManager(object): ... zope.interface.implements(interfaces.IViewletManager) ... index = None ... ... def __init__(self, context, request, view): ... self.context = context ... self.request = request ... self.__parent__ = view ... ... def update(self): ... rows = [] ... for name, value in self.context.items(): ... rows.append( ... [zope.component.getMultiAdapter( ... (value, self.request, self.__parent__, self), ... interfaces.IViewlet, name=colname) ... for colname in shownColumns]) ... [entry.update() for entry in rows[-1]] ... self.rows = rows ... ... def render(self, *args, **kw): ... return self.index(*args, **kw)
Now we need a template to produce the contents table:
>>> tableTemplate = os.path.join(temp_dir, 'table.pt') >>> open(tableTemplate, 'w').write(''' ... <table> ... <tr tal:repeat="row view/rows"> ... <td tal:repeat="column row"> ... <tal:block replace="structure column/render" /> ... </td> ... </tr> ... </table> ... ''')
From the two pieces above, we can generate the final viewlet manager class and register it (it's a bit tedious, I know):
>>> from zope.app.pagetemplate.viewpagetemplatefile import \ ... ViewPageTemplateFile >>> ContentsViewletManager = type( ... 'ContentsViewletManager', (ContentsViewletManager,), ... {'index': ViewPageTemplateFile(tableTemplate)})>>> zope.component.provideAdapter( ... ContentsViewletManager, ... (Container, IDefaultBrowserLayer, zope.interface.Interface), ... interfaces.IViewletManager, name='contents')
Since we have not defined any viewlets yet, the table is totally empty:
>>> contents = Contents(container, request) >>> print contents().strip() <html> <body> <h1>Cotnents</h1> <div> <table> <tr> </tr> <tr> </tr> <tr> </tr> </table> </div> </body> </html>
Now let's create a first viewlet for the manager...
>>> class NameViewlet(object): ... ... def __init__(self, context, request, view, manager): ... self.__parent__ = view ... self.context = context ... ... def update(self): ... pass ... ... def render(self): ... return self.context.__name__
and register it:
>>> zope.component.provideAdapter( ... NameViewlet, ... (IFile, IDefaultBrowserLayer, ... zope.interface.Interface, interfaces.IViewletManager), ... interfaces.IViewlet, name='name')
Note how you register the viewlet on IFile and not on the container. Now we should be able to see the name for each file in the container:
>>> print contents().strip() <html> <body> <h1>Cotnents</h1> <div> <table> <tr> </tr> <tr> </tr> <tr> </tr> </table> </div> </body> </html>
Waaa, nothing there! What happened? Well, we have to tell our user preferences that we want to see the name as a column in the table:
>>> shownColumns = ['name']>>> print contents().strip() <html> <body> <h1>Cotnents</h1> <div> <table> <tr> <td> mypage.html </td> </tr> <tr> <td> data.xml </td> </tr> <tr> <td> test.txt </td> </tr> </table> </div> </body> </html>
Let's now write a second viewlet that will display the size of the object for us:
>>> class SizeViewlet(object): ... ... def __init__(self, context, request, view, manager): ... self.__parent__ = view ... self.context = context ... ... def update(self): ... pass ... ... def render(self): ... return size.interfaces.ISized(self.context).sizeForDisplay()>>> zope.component.provideAdapter( ... SizeViewlet, ... (IFile, IDefaultBrowserLayer, ... zope.interface.Interface, interfaces.IViewletManager), ... interfaces.IViewlet, name='size')
After we added it to the list of shown columns,
>>> shownColumns = ['name', 'size']
we can see an entry for it:
>>> print contents().strip() <html> <body> <h1>Cotnents</h1> <div> <table> <tr> <td> mypage.html </td> <td> 38 bytes </td> </tr> <tr> <td> data.xml </td> <td> 31 bytes </td> </tr> <tr> <td> test.txt </td> <td> 12 bytes </td> </tr> </table> </div> </body> </html>
If we switch the two columns around,
>>> shownColumns = ['size', 'name']
the result will be
>>> print contents().strip() <html> <body> <h1>Cotnents</h1> <div> <table> <tr> <td> 38 bytes </td> <td> mypage.html </td> </tr> <tr> <td> 31 bytes </td> <td> data.xml </td> </tr> <tr> <td> 12 bytes </td> <td> test.txt </td> </tr> </table> </div> </body> </html>
Oftentimes you also want to batch and sort the entries in a table. Since those two features are not part of the view logic, they should be treated with independent components. In this example, we are going to only implement sorting using a simple utility:
>>> class ISorter(zope.interface.Interface): ... ... def sort(values): ... """Sort the values.""">>> class SortByName(object): ... zope.interface.implements(ISorter) ... ... def sort(self, values): ... return sorted(values, lambda x, y: cmp(x.__name__, y.__name__))>>> zope.component.provideUtility(SortByName(), name='name')>>> class SortBySize(object): ... zope.interface.implements(ISorter) ... ... def sort(self, values): ... return sorted( ... values, ... lambda x, y: cmp(size.interfaces.ISized(x).sizeForSorting(), ... size.interfaces.ISized(y).sizeForSorting()))>>> zope.component.provideUtility(SortBySize(), name='size')
Note that we decided to give the sorter utilities the same name as the corresponding viewlet. This convention will make our implementation of the viewlet manager much simpler:
>>> sortByColumn = ''>>> class SortedContentsViewletManager(object): ... zope.interface.implements(interfaces.IViewletManager) ... index = None ... ... def __init__(self, context, request, view): ... self.context = context ... self.request = request ... self.__parent__ = view ... ... def update(self): ... values = self.context.values() ... ... if sortByColumn: ... sorter = zope.component.queryUtility(ISorter, sortByColumn) ... if sorter: ... values = sorter.sort(values) ... ... rows = [] ... for value in values: ... rows.append( ... [zope.component.getMultiAdapter( ... (value, self.request, self.__parent__, self), ... interfaces.IViewlet, name=colname) ... for colname in shownColumns]) ... [entry.update() for entry in rows[-1]] ... self.rows = rows ... ... def render(self, *args, **kw): ... return self.index(*args, **kw)
As you can see, the concern of sorting is cleanly separated from generating the view code. In MVC terms that means that the controller (sort) is logically separated from the view (viewlets). Let's now do the registration dance for the new viewlet manager. We simply override the existing registration:
>>> SortedContentsViewletManager = type( ... 'SortedContentsViewletManager', (SortedContentsViewletManager,), ... {'index': ViewPageTemplateFile(tableTemplate)})>>> zope.component.provideAdapter( ... SortedContentsViewletManager, ... (Container, IDefaultBrowserLayer, zope.interface.Interface), ... interfaces.IViewletManager, name='contents')
Finally we sort the contents by name:
>>> shownColumns = ['name', 'size'] >>> sortByColumn = 'name'>>> print contents().strip() <html> <body> <h1>Cotnents</h1> <div> <table> <tr> <td> data.xml </td> <td> 31 bytes </td> </tr> <tr> <td> mypage.html </td> <td> 38 bytes </td> </tr> <tr> <td> test.txt </td> <td> 12 bytes </td> </tr> </table> </div> </body> </html>
Now let's sort by size:
>>> sortByColumn = 'size'>>> print contents().strip() <html> <body> <h1>Cotnents</h1> <div> <table> <tr> <td> test.txt </td> <td> 12 bytes </td> </tr> <tr> <td> data.xml </td> <td> 31 bytes </td> </tr> <tr> <td> mypage.html </td> <td> 38 bytes </td> </tr> </table> </div> </body> </html>
That's it! As you can see, in a few steps we have built a pretty flexible contents view with selectable columns and sorting. However, there is a lot of room for extending this example:
>>> import shutil >>> shutil.rmtree(temp_dir)