The JFace UI framework
We've seen that the workbench defines extension points for plug-ins to contribute UI function to the platform. Many of these extension points,
particularly wizard extensions, are implemented using classes in the
org.eclipse.jface.* packages. What's the distinction?
JFace is a UI toolkit that provides helper classes for developing UI features
that can be tedious to implement. JFace operates above the level of a raw widget system. It includes classes for handling common
UI programming tasks:
-
Viewers
handle the drudgery of populating, sorting, filtering, and updating widgets.
-
Actions and contributions
introduce semantics for defining user actions and specifying where to make them available.
-
Image and font registries
provide common patterns for handling UI resources.
-
Dialogs and wizards
define a framework for building complex interactions with the
user.
-
Field assist
provides classes that help guide the user in choosing appropriate content
for fields in dialogs, wizards, or forms.
JFace frees you up to focus on the implementation of your specific
plug-in's function, rather than focusing on the underlying widget system or solving problems that are common in almost any UI application.
JFace and the workbench
Where does JFace end and the workbench begin? Sometimes the lines aren't so obvious. In general, the JFace APIs (from the packages
org.eclipse.jface.*) are independent of the workbench extension points and APIs. Conceivably, a JFace program could be written without using any workbench code at all.
The workbench makes use of JFace but attempts to reduce dependencies where possible. For example, the workbench part model
(
IWorkbenchPart)
is designed to be independent of
JFace. We saw earlier that views and editors can be implemented using SWT widgets directly without using any JFace classes. The workbench attempts to remain "JFace neutral" wherever possible, allowing programmers to use the parts of JFace they find useful. In practice, the workbench uses JFace for much of its implementation and there are references to JFace types in API definitions. (For example, the JFace interfaces for
IMenuManager
,
IToolBarManager
, and
IStatusLineManager
show up as types in the workbench
IActionBar
methods.)
When using JFace API, it's a good idea to keep in mind the rules of engagement for
using background threads. See
The workbench and threads for more information.
JFace and SWT
The lines between SWT and JFace are much cleaner. SWT does not depend on any JFace or platform code at all. Many of the SWT examples show how you can build a standalone application.
JFace is designed to provide common application UI function on top of the SWT
library. JFace does not try to "hide" SWT or replace its function. It provides classes and interfaces that handle many of the common tasks associated with programming a dynamic UI using
SWT.
The relationship between JFace and SWT is most clearly demonstrated by looking at viewers and their relationship to SWT widgets.
