AppSuite:Extending the UI

API status: In Development

Extension points:
General information

Abstract. Abstractly speaking extension points are an architecture for letting plugins contribute functionality to other parts of the program. They form the core of the OX App Suite plugin architecture. A less detailed hands-on introduction can be found here. Some basics about the extention point concept and advantages compared to inheritance.

Introduction

Inheritance vs. Extension points

OX App Suite uses the extension point concept to create extension points that allow a simple and flexible way to extending functionality. When system reaches a part that can be extended it asks a central registry if extensions are registered. In that case these extensions will be executes independent of the providing component (some plugin or OX App Suite itself).

The illustrated example compares inheritance and extension points. The main benefit of using extension points is that the programm is still the active component and it's in controll. This leads to the following advantages:

• Reduced coupling
• Increased cohesion
• Modularity- Re-usability
• Dynamic

Some characteristics

• good fences: extension points unregister corrupt extenders
• lazy loading: extenders are loaded if they are used
• fair play: all extenders have equal rights
• diversity: extension points support different extension

Components

The extension point system lives in the 'io.ox/core/extensions' module and consists of these elements:

• extension point system: accessing the outer parts
• registry: manages extension points, extensions and their state
• extension point: part of the systems that can be extended, referenced by a unique id
• extension: adding/replacing functionality during runtime, referenced by a unique id
• baton: object used to store context, passed back through callbacks

Extension Point System

 //load extension points module
 require(['io.ox/core/extensions'], function (ext) {
     //insert code here
 });

Registry

• manages extension points, extensions and their state

list points

 // returns array of point ids
 var keys = ext.keys();

get/create point

 //also registers a point if not happened yet
 var mypoint = ext.point('io.ox/calendar/detail');

Extension Point

• part of the systems that can be extended
• referenced by a unique id
• defines some kind of contract it's extension that to comply

attributes

• id
• description (optional)

example

 //get a point and it's description
 var point = ext.point('io.ox/mail/links/toolbar'),
     descr = point.description = '';

add extension

• important: existing extensions with same id will not be overwritten - use replace insted
• If the id is not specified, the value 'default' is used.
• example: add extension with id 'date'

example

 // chainable (returns mypoint)
 point.extend({
     id: 'example1', // Every extension is supposed to have an id
     index: 100,     // Extensions are ordered based on their indexes
     draw: function () {
         //draw something
     }
 });

replace extension

• important: only extension properties will be replaced (jQuery extend is used internally)
• hint: replace can also be executed before extension is initially created with extend

example

 // chainable (returns mypoint)
 mypoint.replace({
     id: 'example1',
     index: 100,
     draw: function (baton) {
         //draw something completely different
     }
 });

use extensions

• invoking extension point extensions by defining functionname, context and baton
• node used as context (function is called via apply(node, args))
• baton forwarded within programmatic flow and used for storing and exchanging data between extensions

 
mypoint.invoke(name, context, baton);

example

 //call 'draw' of all registered extensions (order defined by index attribute)
 //node used as context ('draw' function is called via apply(node, args))
 //baton's data property contains relevant information about current entity (for example a mail object)
 mypoint.invoke('draw', node, baton);

access extensions

 
// returns array containing all extension ids
mypoint.keys();

// returns array containing all extensions
mypoint.all();

// executes callback for a specific extension; chainable (returns point)
mypoint.get(id, callback);

// disabled extension will return true also;
var exists = mypoint.has(id);

enabled only

// returns array containing all enabled extensions
mypoint.list();

// returns number containing enabled extensions
mypoint.count();

enabling/disabling

var enabled = mypoint.isEnabled();

 // chainable (returns mypoint)
 mypoint.enable(id);

 // chainable (returns mypoint)
 mypoint.disable(id);

example

 //disable
 ext.point('io.ox/mail/detail/header').disable('receiveddate');

underscore equivalents

• only considers enabled extensions
• functions returns underscore-chain object of enabled extensions
• take a look at [ http://underscorejs.org ] for more details

 mypoint.chain();
 mypoint.each(callback);
 mypoint.map(callback);
 mypoint.filter(callback); //select alias
 mypoint.reduce(callback, memo); //inject alias
 mypoint.pluck(propertyName);

example

 // Shuffle extension order
 ext.point('io.ox/calendar/detail').each(function (e) {
     e.index = Math.random() * 1000 >> 0;
 }).sort();

Event Hub

• Event Hub based on jQuery's on, off, one and trigger
• differences documentated for each function

 // attach listener
 mypoint.on(type, data, function);

 // detach listener
 mypoint.off(type, function);

 // attach listener for a single execution
 mypoint.one(type, data, function);

 // trigger event
 // difference: allows multiple types separated by spaces.
 // difference: actually calls triggerHandler since we are not in the DOM.
 mypoint.trigger(types);

 // explicit destroy to clean up.
 mypoint.destroy();

Extension

• adding/replacing functionality during runtime
• referenced by a unique id

Attributes

• id
• index (optional): numeric value used for specify order of execution (also valid are 'first' and 'last')
• functions: as required by the extension point contract

'example

 
//defining a extension for some extension point that requires a draw function
{
    id: 'example1',
    index: 100,
    draw: function () {
        //draw something
    }
};

execution order

To ensure your extension is called first or last use the index 'first' or 'last'. Keep in mind that a defined call order does not guarantees all extensions with a lower index finished already when your extension is called (for example some asynchronous code). Nevertheless for the most common use case (draw extensions that create/modify nodes with already present data) this execution order should be quite reliable to do some DOM manipulation within an custom extension indexed as 'last'. If more than one extension of a point has the index 'first' or 'last' these will be executed first/last in the order they were added.

extensions patterns

OX App Suite uses extensions patterns. Please keep in mind that this list not necessarily covers all pattern currently used.

io.ox/backbone/forms.js

• CheckBoxField
• ControlGroup
• DateControlGroup
• DatePicker
• ErrorAlert
• Header
• InputField
• Section
• SectionLegend
• SelectBoxField
• SelectControlGroup

io.ox/backbone/views.js

• AttributeView

io.ox/calendar/edit/recurrence-view

• RecurrenceView

io.ox/core/extPatterns/links

• Button
• DropdownLinks
• InlineLinks
• link
• ToolbarLinks

io.ox/core/tk/attachments

• AttachmentList
• EditableAttachmentList

io.ox/contacts/widgets/pictureUpload.js

io.ox/preview/main.js

• Engine

Baton

Part of extension points system is a structure called baton which serves as an context object. The baton passed back through callbacks within programmatic flow allowing data exchange between extension points.

attributes

• data: usually contains current entity object, also used for data exchange
• options: contains data such as the current active application if a baton is used comprehensively
• flow:
  • disabled: stores disabled extensions (managed via baton.disable(pointId, extensionId))
    
• $: used to reference a jQuery node object

disable extensions

 //disable
 baton.disable(pointid, extensionid);

 //is disabled
 var isDisabled = baton.isDisabled(pointid, extensionid);

example

 var pointid = 'io.ox/mail/detail',
     extensionid = 'example3',
     node = $('div'),
     baton = ext.Baton();

 //disable extension
 //returns undefined
 baton.disable(pointid,extensionid);

 //invoke extension with baton instance 
 ext.point(pointid).invoke('draw', node, baton)

data exchange

example

 //extension using baton to store data
 {
     id: 'example1',
     index: 100,
     draw: function (baton) {
         //get the currenty process mail object
         var mail = baton.data;
         //append subject to current node referenced as this
         this.append(
             $('div').text(mail.subject);
         )
         //extend mail object to store some flag
         mail.drawn = mail.drawn || {};
         mail.drawn.subject = true;
         //disable extension3
         baton.disable()
     }
 };
 {
     id: 'example2',
     index: 200,
     draw: function (baton) {
         //get the currenty process mail object
         var mail = baton.data;
         //use value set by 'example1'
         if(mail && mail.drawn && mail.drawn.subject) {
             //do something
         }
     }
 };
 {
     id: 'example3',
     index: 300,
     draw: function (baton) {
         //wil not be executed if baton from 'disable example' is used
     }
 };

ensure

• ensure that submitted object is instanceof baton
• return obj if it's an instanceof baton
• return new baton instance where baton.data is extended by obj or obj.data (if exists)

 var baton = ext.Baton.ensure(obj) 

example

 //new baton.data extended by object
 var baton = ext.Baton.ensure({ id: 2 })

Conclusion

As you can see, unlike adding functionality, customizing and modifying existing extensions is always more of a grey box operation and might incur some risks when updating the software. For example when replacing a certain functionality parts of the original functionality will have to be reimplemented, and all that extra code will have to be maintained in the future.

In essence extension points are better suited to integrating new functionality into the product rather than customizing existing functionality, but, when in a pinch or really wanting to change a certain part of the software, this is certainly a way to consider. At its most extreme use you could even disable all extensions for the mail detail view to register a set of your own extensions to completely change the way mails are displayed, at the cost of having to maintain your own detail view.

This wraps up our little tour of the OX App Suite extension point system. It is used to integrate new functionality into the OX App Suite and provides a system for 3rd party applications to become extensible themselves. It can be used to customize the existing UI at the cost of havint to know a bit more about the internals of our application. For now until more comprehensive documentation becomes available, look at the existing OX App Suite code to see concrete extensions and extension points in action.