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Differences between RWT and SWT

Introduction to the RAP Widget Toolkit

At the core of RAP operates the RAP Widget Toolkit (RWT), which largely implements the same API as the Standard Widget Toolkit (SWT). That is why many projects that build upon SWT (like JFace) can run on RWT with little or no modifications. It can also be used with or without the Eclipse 3.x workbench layer.

Note that RWT refers only to this widget toolkit, while RAP refers to the project in its entirety, including its ports of JFace, Workbench and Forms, OSGI integration, add-ons, Branding and Interaction Design API, tooling, demos and custom themes.

RWT implements most (40+) SWT Widgets, including their events and layout manager. It also supports SWT-like key and mouse event handling, drag and drop and painting (on Canvas). If you are not already familiar with SWT, we recommend to first learn the SWT basics (almost all valid for RWT) by reading the official documentation and snippets provided by the SWT project homepage. A full reference specific to RWT can be found here.

Compatibility to SWT

RAP generally follows the rule If it compiles, it works. That means that all SWT API implemented in RWT is working within the requirements set by SWT. If an SWT feature is not implemented, the corresponding API is also missing. If this is the case, it is likely because it's hard or impossible to implement in RWT. In some cases, SWT classes and methods are implemented as empty stubs to enable single-sourcing, but only where this is a valid according of the SWT documentation of the API. Examples are the accessibility API and some SWT constants that are marked as HINT.

SWT was developed for desktop applications, but RWT is used to build web applications. For this reason, there are some features that SWT supports that RWT does not, while RWT adds some features that are tailored to the specific requirements of web application development. However, RWT does not add any new API to the classes adopted from SWT. All RWT-specific features are accessible by API in the namespace org.eclipse.rap.rwt. Many are activated using a widget's setData method with a constant from the RWT class as the key. Example:

table.setData( RWT.MARKUP_ENABLED, Boolean.TRUE )

Other additional features may be accessed via client services.

Notable Additional Features

  • Client Class and Client Services
    All features specific to the RAP client (which is exchangeable) are handled by the client class and the client services. This includes support for browser history, JavaScript execution and retrieving the clients time zone offset. The Client interface and client services are documented in more detail here.
  • HTTP File Upload
    Unlike SWT, RWT can not simply access the user's file system and read data from it. Therefore RAP provides several ways to upload files within the RAP application. Read more about it here.
  • Markup in Widgets
    Several widgets in RWT support a subset of HTML in their text property. Detailed information can be found here.
  • Tree and Table Enhancements
    The RWT Tree and Table widgets provide a number of features not found in SWT. This includes the possibility to exclude some columns from scrolling, pre-caching of items, as well as support for templates, markup and advanced theming. Find out more about it here.
  • DropDown Widget
    The DropDown widget enables simple and efficient input assist for text fields. It is basically a pop-up list that can be attached to any Text widget. It behaves very similar to Combo, but does not automatically change the content of the widget it is attached to. Instead it fires selection events that may be used to modify the value of the Text widget programatically.
    A ready-to-use, enhanced auto-complete solution for text fields can be found in the RAP Incubator. The component is called AutoSuggest and uses the DropDown widget internally.
  • Theming
    In SWT, the default visual representation of an widget is determined by the operating system. In RAP this is done by the theming which can be adjusted by the developer using CSS.
  • Multi-User Environment
    RAP operates in a multi-user environment and provides some additional API that helps dealing with the consequences. An detailed introduction can be found here.
  • Scripting
    Since the RAP WebClient is JavaScript based you can also write event listeners in JavaScript instead of Java. This may be used to implement features that require instantaneous user feedback or rely heavily on key events. Read more about it in the Scripting section.

Notable Limitations

  • Unimplemented Features
    While the API for touch event handling and accessibility configuration is present in RWT, it does not natively support either. This is a valid implementation according to the SWT documentation. Accessibility in RAP may be achieved by adding ARIA attributes though.
  • Unimplemented Widgets: StyledText, Tracker, TaskBar, Tray
    These widgets are currently not available in RWT. If you require a rich text editor in RAP, take a look in the RAP Incubator and Wiki.
  • Painting Limitations
    SWT can paint on any widget or image using a GC, while RAP only allows painting on the Canvas widget. In some cases the drawText, drawString and drawImage methods may disregard the drawing order and overlap elements that are drawn later. Some methods are unimplemented, including copyArea, setClipping, setTransform, setInterpolation, setLineDash and setXORMode. Performance and results of a drawing operations can differ depending on the browser. It is possible to use the native HTML5 Canvas directly instead of the SWT GC using RWT Scripting. See also Self-Drawing custom widgets.
  • Limitations in Dialogs: Dialog, ColorDialog, FontDialog, MessageBox
    When using the JEE compatibility mode, opening a dialog does not block program execution. To obtain their return value, a callback must be registered using the RWT-only open(DialogCallback) method.
  • Limitations of the Browser widget
    Since the Browser widget is based on the HTML iframe element, there are some restrictions. Detailed information can be found here. Also, when using the JEE compatibility mode, evaluating a script does not block program execution. To obtain its return value, a callback must be registered using the RWT-only evaluate(String, BrowserCallback) method.
  • Limitations in Mouse and Key Events
    See Mouse and Key Event Handling in RAP.
  • Limitations in Verify and Modify Events:
    Modify and Verify events are not fired instantaneously, but with a small delay, possibly combining a number of changes into one event. Also, the values of the VerifyEvent fields text, start and end currently always report the entire text to have changed. However, when using a ClientListener (written in JavaScript), these limitations do not exist.
  • Limitations in Drag and Drop
    In DragSourceEvent, the fields image, offsetX and offsetY have no effect. DropTargetEvents may be omitted while the mouse cursor is still in motion. When dragging files from the clients OS (to drop on a drop target with ClientFileTransfer), feedback effects are not renderd, operation types (move/copy/link) are ignored, and no DragEnter / DragOver / DragLeave events are fired.
  • Limitations when using background threads
    See articles Session access from a background thread and Server Push.