[Zope3-Users] Re: Intended scope of viewlets?

[Jürgen Kartnaller]

Hi Alec.

Alec Munro wrote:
> Hi List,
> 
> I'm just getting up to speed with viewlets, having read a thread here
> and there in the past about them. I've installed the examples provided
> on this list, and while I believe I understand how they work, I don't
> understand in what circumstances they are most useful. The viewlets in
> the examples are all very small, such as retrieving an formatting a
> single piece of information about an object. However, from some of the
> posts to this list, I get the impression they are also being used for
> more complex items, like navigation menus.

Menus are a perfect example for the use of viewlets.
Have a look at z3c.menu. This package contains a base implementation for 
menus based on viewlets.

> Is there a recommended scope? Can they be described in a way such as
> "develop your templates up to point X, then use a viewlet for
> development of further depth?".
> 
> In my case, I am developing a new skin for a project, and my
> experience with metal says to make the entire HTML page a macro with
> slots for content and navigation. Is there a comparable viewlet-based
> paradigm?

Yes there is one, see below

> 
> Also, am I correct in stating that when working with viewlets, the
> only complete HTML page will be the primary skin file, with all
> viewlets based on snippets of HTML?

Thats exacly what we at Lovely Systems do and it works perfectly :)

We have one base template which is used for all pages. Instead of 
defining slots to be filled by other templates it contains viewlet managers.
We then provide different view classes to be able to register our 
viewlets for the pages of the application.
The view classes are empty classes they are just providing the class 
name or if they provide additional functionality they also provide an 
interface.
It is then possible to register the viewlets for specific pages.
The most important thing on viewlets is that they are adapters on the 
*context*, the *request*, the *view* and the *manager*.

The viewlet solution is an extremely productive way to implement a 
complex application.

Make sure you read this :
http://blogs.lovelysystems.com/srichter/2006/09/20/the-skin-browser-and-lovely-systems-new-development-workflow/

Stephan Richter describes here our use of the viewlet concept and our 
development workflow. The most important part was the development of the 
package z3c.viewtemplate. This package makes it possible to separate the 
  development of the HTML page from the implementation of the python 
view class. The package is not yet perfect but gives us what we need 
right now but it needs a better integration into forms and viewlets. 
Expect more in the near future!

In our applications really everything is done using viewlets, there is 
no single use of fill-slot in the hole application!

> 
> My questions are fairly broad-ranging, I know, but I have thus far
> been unable to find a straightforward explanation of viewlets, in
> terms of how they relate to general site development.

All I can tell you now is : USE VIEWLETS, USE VIEWLETS, USE VIEWLETS,


Jürgen