CompositePage is a way to assemble web pages from page fragments. Through the use of Zope page templates, browser-based drag and drop, and custom context menus, CompositePage makes it easy to visually combine page fragments into complete pages.
How to use CompositePage
Follow these steps:
- Install the CompositePage product in Zope by unpacking the archive into your Products directory. I’ve tested only with a current Zope checkout, which is something like Zope 2.7.
- Create a Composite Tool instance in a central location, possibly the root folder.
- Create a Composite object. On the creation form, there is a checkbox for creating a sample template. Leave the checkbox checked.
- Visit the Composite object and select the “Design” tab. You should see a three-column layout with blue dotted lines in the places where you are allowed to insert content.
- Click just beneath one of the blue lines. A context menu will pop up. Select “Add…”.
- You will be directed to a slot (a folderish object.) In slots, you can add composite elements. Add a composite element that points to a script.
- Find the composite created earlier and select the “Design” tab again. Your new object should now show up in the slot.
- Move the object to a different slot using drag and drop. When the mouse cursor is hovering over a permitted target (the blue dotted lines are targets), the target will be highlighted. Let go and watch your object appear in the new place.
- Right-click over your object and select “Delete” from the context menu.
How to write a template
Templates can be any Zope object, but ZPTs (Zope Page Templates) are the most common. A template designed for use with composites uses the ‘slots’ attribute of the composite. The ‘slots’ attribute is a mapping-like object.
Here is a simple composite-aware page template:
<html> <head> </head> <body> <div tal:content="structure here/slots/center/single"> This will be replaced with one element from one slot. </div> </body> </html>
The expression ‘here/slots/center/single’ gets the ‘slots’ attribute of the composite, finds a slot named ‘center’, and calls the single() method of the slot, returning a string containing an HTML structure.
The only place you have to name a slot is in the template. If the template refers to a slot that does not yet exist, the composite will create and return an empty slot. If you place something in that slot using the drag and drop interface, the composite will transparently add a new slot to the ‘filled_slots’ folder. Note that Zope prevents you from storing slots with names that start with an underscore or that clash existing folder attributes.
Templates use either the single() or the multiple() method of a slot. single() returns a string, while multiple() returns a list of strings. Use single() when you expect the slot to never contain more than one element. Use multiple() to allow more than one element. In either case, don’t forget to use the ZPT ‘structure’ keyword, since the returned strings contain HTML that should not be escaped.
You can also use the special slot expression type to define slots in a template:
<html> <head> </head> <body> <div tal:content="slot: center"> This will be replaced with elements in the center slot. </div> </body> </html>
This syntax allows the template author to define slot titles in addition to slot names. The template author could write:
<div tal:content="slot: center 'Page Center'">
The slot title will be shown to page designers.
How it works
When you render (view) a composite, it calls its template. When the template refers to a slot, the composite looks for the named slot in the filled_slots folder. If it finds the slot, it returns it; if it doesn’t find it, the composite creates a temporary empty slot. Then the template calls either the single() or multiple() method and the slot renders and returns its contents.
Rendering in edit mode
When requested, the composite calls upon a “UI” object to render its template and slots with edit mode turned on. In edit mode, slots add ‘class’, ‘source_path’, ‘target_path’, and ‘target_index’ attributes to HTML tags to mark movable objects and available drop targets. Slots add HTML markup for drop targets automatically. When rendering using the single() method, slots provide a drop target only if the slot is empty. When rendering using the multiple() method, slots insert drop targets between the elements and to the beginning and end of the slot.
The UI object can use various mechanisms to make the page editable. Most UI objects use regular expressions to find the ‘head’ and ‘body’ tags. Then the UI object inserts scripts, styles, and HTML elements. The result of the transformation is sent back to the browser.
Drag and drop
Adapting CompositePage to other applications
CompositePage provides a default user interface that integrates with the Zope management interface, but mechanisms are provided for integrating with any user interface. Look at design.py, the ‘common’ subdirectory, and the ‘zmi’ subdirectory for guidance. Simple customizations probably do not require more code than the ZMI UI.
Fixed test failures caused by 7 years of changes to Zope and Python. This mostly involved simple modernization:
- Use zope.interface, zope.tales, and zope.pagetemplate rather than their predecessors.
- Use absolute imports.
- Use Unicode where possible.
Let’s stop swallowing errors that occur when rendering the template to get the list of slots. Error messages are friendlier than silent breakage.
Slots now show the add element interface only at the top and bottom of the slot, not between elements. (Hmm, should this be configurable?)
- Changed the UI to use images for elements and targets.
- Added inline views. You can now select templates to render objects.
- Context menus now have headers.
- The clipboard now works.
- You can now define slots in a template using “slot:” expressions. This should make it easier to write templates.
- The composite tool now checks copy/paste permissions before making any changes.
- Slots now have a __str__ method, making it easy to render them directly.
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