OOUI/Creating interfaces programmatically

The OOjs UI library provides the building blocks for building an object oriented user interface. It includes many widgets and layouts that are ready to use, as well as basic elements which can be composed to build something of your own. Complex systems such as windowing and toolbars are also provided, and can be extended and composed to fit your application’s needs.

User interfaces are created programmatically in OOjs UI, which abstracts away HTML markup entirely. This technique allows the markup to change, so long as the APIs that generate the markup remain stable. Markup may change when extending a class to support a new feature, or when fixing a bug to increase compatibility.

Everything in OOjs UI that the user can see is built using elements, which are composed together to form discrete parts of a user interface, and also to bring those parts together. By maximizing element reuse, visual, behavioral and API consistency is easier to maintain.

Getting started
If you are not yet familiar with how interfaces are created with OOjs UI, this section contains a quick tutorial on how to build a widget using the library.

Creating a widget involves two basic steps: Note that OOjs UI objects must be added to the DOM before they are visible to the user. Developers writing code should account for the fact that a widget may or may not be attached to the DOM, and will never be attached to the DOM during the execution of the constructor. Even after an element has been attached, it may later become detached. You can check if the element is currently attached using the .isElementAttached method.
 * 1) The widget is created and configured
 * 2) The widget is added to the DOM

Remember to include the required libraries (jQuery and OOjs) as well as the relevant style information (one of the OOjs UI themes, currently Apex or MediaWiki) and the OOjs UI library itself.

Creating and configuring a widget
Each widget is created and configured with either a configuration object that is passed to the widget constructor or by using methods to set the configurations (see example below). Many of the library’s methods are chainable, as illustrated in the example.

Once the widget has been created and configured, it must be attached to the DOM in order to be visible to the user. Use the jQuery .append method to insert the new widget into the DOM using its $element property.

The following example demonstrates how to create and append a simple ButtonWidget that, when clicked, will open “http://www.mediawiki.org” in a new window. ‘button1’ is configured using a config object. ‘button2’ is configured using the widget’s methods:

Note that some get methods (e.g. getItemFromData or getElementDocument ) should not be chained. These methods may return ‘null’, and trying to call another method on ‘null’ will cause an error.

Connecting an event handler to a widget
Widgets emit events when they are interacted with or changed in an interesting way. These events can be listened to by connecting event handlers to the widget. The below example uses an event handler to display an alert when the button is clicked. When the button is clicked, its label will be reset to read ‘Do not click me!’ via the button’s setLabel method.

Event handling is provided by the EventEmitter class, which is “mixed in” to all widgets. For more information about EventEmitter, please see OOjs primer.

Understanding mixins
The concept of mixins is fundamental to the library, and many of the library’s elements can be customized via mixin functionality. For example, one can easily add an icon to a button widget by taking advantage of the fact that the IconElement class is mixed in to the ButtonWidget class. Mixin classes can be used to create and add new elements to a widget (such as the icon in the above example) or to add new behaviors (such as new methods for handling styling flags or titles).

There are three kinds of element mixins, each identified with a naming convention:  Note that though a mixin class can create and initialize an object, it will not append it to the DOM. This must be done manually if you wish to manipulate the object directly.
 * Content: Content mixins generate elements by default (e.g., groups, icons, indicators and labels). The names of content mixins have no suffix (e.g., GroupElement, IconElement, etc.)
 * Attribute: Attribute mixins operate on $element by default (e.g., flags and titles). The names of attribute mixins have an "ed" suffix (e.g., FlaggedElement, TitledElement, etc.)
 * Behavior: Behavior mixins operate on $element by default (e.g., clippable). Behavior mixins are identified with an ”able" suffix (e.g., ClippableElement, etc.) 

It is not uncommon to see widgets composed of multiple mixins: for example, the ButtonWidget class utilizes ButtonElement and IconElement mixins (and a few others). One can easily see which classes have been mixed and are available in the code-level documentation for each class. Mixin classes will always be displayed in the upper right of the documentation screen for each class. In addition each Config option notes the name of the class that defines it.