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<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<article id="article">
<articleinfo>
<title>Swing/SWT Integration</title>
<releaseinfo role="SVN"> $Id: article.xml,v 1.3 2007/06/20 15:33:53 wbeaton Exp $ </releaseinfo>
<date>June 20, 2007</date>
<authorgroup>
<author>
<firstname>Gordon</firstname>
<surname>Hirsch</surname>
<affiliation>
<orgname>SAS Institute Inc.</orgname>
</affiliation>
</author>
</authorgroup>
<copyright>
<year>2007</year>
<holder>SAS Institute Inc. Made available under the EPL v1.0 </holder>
</copyright>
<abstract>
<para>
Swing and SWT are sometimes seen as strictly competing technologies. Some
people have strong opinions on which UI toolkit to use exclusively for client
applications. However, in the real world, ideological extremes are
often impractical. Some valid use cases require both technologies
to coexist in a single application. While mixing the two toolkits is not a
simple task, it can be done, and it can be done such that the two toolkits
are smoothly integrated. This article discusses the steps necessary to
achieve good Swing/SWT integration. It focuses on the use case of embedding
existing Swing components into an SWT-based Rich Client Platform application.
</para>
</abstract>
<legalnotice>
<para>Java and all Java-based trademarks are trademarks of Sun Microsystems, Inc. in
the United States, other countries, or both.</para>
<para>Other company, product, or service names may be trademarks or service marks of
others.</para>
</legalnotice>
</articleinfo>
<section id="sec-introduction">
<title>Introduction</title>
<para>
Many existing standalone Java clients represent a large investment in Swing
components. While there are compelling arguments for moving these clients to the Eclipse Rich
Client Platform (RCP), the full migration of a large existing application can be
expensive. By retaining some Swing components, the initial cost of
migration can be reduced. Over time, Swing components may be incrementally converted
to SWT if and when it becomes necessary.
</para>
<para>
For example, at SAS we have extended the standard Swing <ulink url="http://java.sun.com/j2se/1.5.0/docs/api/javax/swing/JTable.html">
<code>JTable</code></ulink> component to
create an enhanced table that meets the needs of our existing applications.
A large effort will be required to convert this component to SWT. Instead of
waiting for an equivalent SWT table, we are able to use the Swing
table component as-is in an RCP application, as shown in the screenshot below.
It shows an RCP application running on the Windows XP platform.
The two tables are Swing components; all other components
were created with SWT.
</para>
<figure id="fig-table-embed">
<title>Embedding Swing Table Components</title>
<mediaobject>
<imageobject>
<imagedata fileref="images/table-embed.png"/>
</imageobject>
</mediaobject>
</figure>
<para>
We also have a large inventory of complex Swing components to display graphs and charts.
Again, by mixing Swing and SWT, we can consider the conversion of these Swing components separately from
the immediate needs of an application that we'd like to migrate to RCP.
The screenshot below shows another RCP application with a Swing-based graph
component. Everything else in the image is an
SWT component. (This application may not look like an RCP application,
but it is. The unusual look is due to extensive use of the Eclipse
presentations API and other advanced workbench features.)
</para>
<figure id="fig-graph-embed">
<title>Embedding Graphical Swing Components</title>
<mediaobject>
<imageobject>
<imagedata fileref="images/graph-embed.jpg"/>
</imageobject>
</mediaobject>
</figure>
<para>
The use of Swing components with the RCP implies that two large UI toolkits will coexist in a
single application and that some amount of integration is necessary to ensure UI
consistency across the entire application.
</para>
<para>
SWT provides the SWT/AWT Bridge <xref linkend="bib-bridge"/> as the basic infrastructure for Swing/SWT integration.
However, the bridge is only the first step along the
path to embedding usable Swing components in RCP applications. Much of
this article is devoted to explaining the additional practices necessary for
effective integration. Without these practices, the
SWT/AWT Bridge is insufficient for production-quality application use.
With them, you can successfully host key Swing components in RCP
applications.
</para>
<para>
Integrating two independent UI toolkits is a complicated task, and it
rarely produces perfect results. This article
concentrates on practical techniques (and yes, even some hacks) to make the
integration effective enough for use in real-world applications.
</para>
<para>
Despite the complexity, most of the practices described below can be encapsulated
in a single common base class to be used when embedding Swing components. There are additional
helper classes to support the implementation. An example is included with this
article. See <xref linkend="app-example-code"/> for more information.
</para>
</section>
<section id="sec-using-bridge">
<title>Using the SWT/AWT Bridge</title>
<para>
The SWT/AWT Bridge has been part of SWT since version 3.0. It is
a very simple API, located in the package
<code>
<ulink
url="http://help.eclipse.org/help32/topic/org.eclipse.platform.doc.isv/reference/api/org/eclipse/swt/awt/package-summary.html">
org.eclipse.swt.awt</ulink>.
</code>
</para>
<note>
<para>
This article focuses on embedding AWT frames inside SWT composites. It demonstrates only
one half of the SWT/AWT Bridge. Nevertheless, most of the improvements described below also apply to the
other direction: embedding SWT composites inside AWT frames.
</para>
</note>
<para>Minimally, embedding an AWT frame inside an SWT composite is just two simple lines of code</para>
<programlisting>
Composite composite = new Composite(parent, SWT.EMBEDDED | SWT.NO_BACKGROUND);
Frame frame = SWT_AWT.new_Frame(composite);
</programlisting>
<para>
An instance of <code>org.eclipse.swt.Composite</code> is created with the <code>SWT.EMBEDDED</code>
style. This style signals that an AWT frame is to be embedded inside the Composite. The call to the static <code>new_Frame</code>
method creates and returns such a frame. The frame may then be
populated with AWT and/or Swing components.
</para>
<para>
The returned frame is not a standard AWT frame. By default, it is a subclass of <code>java.awt.Frame</code>
that is meant to be embedded within native applications. In fact, it is the same frame that is used to
embed <ulink url="http://java.sun.com/applets/">applets</ulink> inside a browser window.
</para>
<para>
The example code shown above is deceptively simple. While SWT does much under the covers to manage the
integration of the two toolkits, the scope of the bridge's implementation is very narrow. In reality, you must do much
more in your application to make the integration more consistent. These additional steps are
described below in <xref linkend="sec-adding-to-bridge"/>.
</para>
<section id="sec-platform">
<title>Platform Considerations</title>
<para>
There are version constraints for using the SWT/AWT Bridge that differ from platform to
platform.
</para>
<table id="version-table" frame='all'>
<title>Minimum Versions</title>
<tgroup cols='3' align='left' colsep='1' rowsep='1'>
<colspec colname='c1' />
<colspec colname='c2' />
<colspec colname='c3' />
<thead>
<row>
<entry>Platform</entry>
<entry>JRE Version</entry>
<entry>Eclipse Version</entry>
</row>
</thead>
<tbody>
<row>
<entry>Windows</entry>
<entry>1.4</entry>
<entry>3.0</entry>
</row>
<row>
<entry>Linux/GTK</entry>
<entry>1.5</entry>
<entry>3.0</entry>
</row>
<row>
<entry>Mac OS X</entry>
<entry>1.5.0 Release 4</entry>
<entry>3.2</entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
Mac OS X also requires installation of the SWT Compatibility
Libraries. See the SWT
<ulink url="http://www.eclipse.org/swt/faq.php#swtawtosx">FAQ</ulink>
for details. Also, as of the writing of this article, the SWT/AWT Bridge on
Mac OS X is not yet complete. See bug
<ulink url="https://bugs.eclipse.org/bugs/show_bug.cgi?id=145890">
145890
</ulink>
for details.
</para>
</note>
<note>
<para>
As of the writing of this article, use of the SWT/AWT Bridge causes hangs
with Java 6 with the GTK look and feel on the Linux/GTK platform. Refer to
Eclipse bug
<ulink url="https://bugs.eclipse.org/bugs/show_bug.cgi?id=91157">91157</ulink>
and Sun bug
<ulink url="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6386791">
6386791
</ulink>
for more information.
</para>
</note>
</section>
<section id="sec-event-threads">
<title>Multiple Event Threads</title>
<para>
Swing/SWT integration has important threading implications. Each UI toolkit has its own
event queue, and each event queue is processed by a separate thread. Most SWT
APIs must be called from the SWT event thread. Swing has similar
restrictions though they are not as strictly enforced.
This split is the major drawback of mixing the toolkits, and it adds some
complexity to the code.
</para>
<para>
Applications must be aware of the current thread, and, where necessary,
schedule tasks to run on the appropriate UI toolkit thread. To schedule work on
the AWT event thread, use:
</para>
<itemizedlist>
<listitem>
<simpara>
<code>javax.swing.SwingUtilities.invokeLater()</code>
</simpara>
</listitem>
<listitem>
<simpara>
<code>javax.swing.SwingUtilities.invokeAndWait()</code>
</simpara>
</listitem>
</itemizedlist>
<para>To schedule work on the SWT event thread, use:</para>
<itemizedlist>
<listitem>
<simpara>
<code>org.eclipse.swt.widgets.Display.asyncExec()</code>
</simpara>
</listitem>
<listitem>
<simpara>
<code>org.eclipse.swt.widgets.Display.syncExec()</code>
</simpara>
</listitem>
</itemizedlist>
<para>
These are the same APIs used in a single-toolkit environment
to keep the UI responsive while offloading long running operations to a worker
thread. With Swing/SWT integration they are used for the
additional purpose of moving work from one event thread to another.
</para>
<para>
The use of multiple event threads increases the risk of deadlock.
Whenever possible, try to avoid blocking one event thread while
scheduling work on the other event thread. In other words,
avoid calling <code>SwingUtilities.invokeAndWait</code> from the SWT event
thread and avoid calling <code>Display.syncExec</code> from the AWT event thread.
Otherwise, if there's ever a case where one blocking call is made while the
other thread has made its own blocking call in the other direction,
deadlock will occur.
</para>
</section>
</section>
<section id="sec-adding-to-bridge">
<title>Building on the SWT/AWT Bridge</title>
<para>
If you use the SWT/AWT Bridge API alone, Swing components will integrate poorly
into your application. The following sections
describe the integration problems in detail and suggest solutions. All of the solutions
involve additional code to help manage the Swing/SWT integration. The
good news is that this code can be encapsulated in a single custom
embedded composite widget (and some support classes), and it can be decoupled from
the rest of the application
code.
</para>
<section id="sec-look-and-feel">
<title>Configuring the Swing Look and Feel</title>
<para>
Here's an example showing some very basic visual problems that result from
minimal use of the SWT/AWT Bridge on the Windows platform.
</para>
<figure id="fig-badembed">
<title>Minimal Embedding of a Swing Component</title>
<mediaobject>
<imageobject>
<imagedata fileref="images/badembed.jpg"/>
</imageobject>
</mediaobject>
</figure>
<para>
There are some immediately obvious problems here. The header and scrollbars on the Swing
<code>JTable</code> (upper right) differ from the SWT-based Error Log view.
</para>
<para>
In this example, the <code>JTable</code> is displayed with the standard
Swing cross-platform (Metal)
<ulink
url="http://java.sun.com/docs/books/tutorial/ui/features/plaf.html">
look and feel
</ulink>.
On the other hand, the
SWT components use underlying native widgets
which have a native look and feel. Swing's
look and feel must be changed to match the
native platform. Since the SWT/AWT Bridge itself does not automatically set
the native look and feel, it's necessary to do it yourself. For
example,
</para>
<programlisting>
import javax.swing.UIManager;
...
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
...
</programlisting>
<para>
Make this call once, before any
AWT or Swing components are created.
</para>
<tip>
<para>
Linux/GTK developers: depending on the window manager in use, the Swing system
look and feel may not be set to the GTK look and feel. It may be necessary to
set the GTK look and feel more explicitly:
<programlisting>
UIManager.setLookAndFeel("com.sun.java.swing.plaf.gtk.GTKLookAndFeel");
</programlisting>
</para>
</tip>
</section>
<section id="sec-root-pane-container">
<title>Creating a Root Pane Container</title>
<para>
The
<code>SWT_AWT.new_Frame()</code>
method returns an instance of a subclass of <code>java.awt.Frame</code> that has been embedded within an SWT
<code>Composite</code>. There are certain rules that must be followed when using
an embedded frame in Swing.
</para>
<itemizedlist>
<listitem>
<para>
The first child of the embedded frame must be a heavyweight component. The
component must fill the entire frame. This heavyweight component allows for correct mouse locations and
interactions. See Sun bug <ulink url="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4982522">4982522</ulink>
for more information.
</para>
</listitem>
<listitem>
<para>
To make the frame viable for use with Swing, you must also create a
<ulink
url="http://java.sun.com/j2se/1.5.0/docs/api/javax/swing/JRootPane.html">
root pane
</ulink>container (<code>javax.swing.RootPaneContainer</code>). The root pane is the basis for all Swing windows. It provides the layering
capabilities on which all Swing components depend.
</para>
</listitem>
<listitem>
<para>
Due to assumptions in the Swing implementation, the root pane container
should be an instance of <code>JFrame</code>, <code>JDialog</code>, <code>JWindow</code>, or <code>JApplet</code>.
Of these options,
only <code>JApplet</code> is an appropriate choice, since it is the only one that can
be embedded.
</para>
</listitem>
</itemizedlist>
<para>
To satisfy each of these rules, create a <code>JApplet</code> as the only child of the
embedded frame. Use of <code>JApplet</code> does not imply that you have created a true
applet with an applet's lifecycle; you are simply using the same display
container as an applet embedded in a browser.
</para>
<programlisting>
Composite composite = new Composite(parent, SWT.EMBEDDED | SWT.NO_BACKGROUND);
Frame frame = SWT_AWT.new_Frame(composite);
JApplet applet = new JApplet();
frame.add(applet);
</programlisting>
<note>
<para>
The embedded frame is a window (a subclass of <code>java.awt.Window</code>). As such,
it consumes resources. For this reason we encourage the use of embedded
frames as replacements for larger components rather than smaller ones.
</para>
</note>
</section>
<section id="sec-reducing-flicker">
<title>Reducing Flicker</title>
<para>
Use of the SWT/AWT Bridge, without additional measures, causes excessive
flicker in an embedded AWT frame while the application window is resized. The
reasons include:
</para>
<itemizedlist>
<listitem>
<para>
A heavyweight component (<code>javax.swing.JApplet</code>, in our case) is present in the component
hierarchy. The AWT implementation, by default, clears the component's background on every resize event.
</para>
</listitem>
<listitem>
<para>
More resize events are handled by the embedded frame, when compared to the default
behavior in a standalone Swing application. This increase is due to the way resize
events are passed on to the AWT frame from the enclosing SWT composite.
</para>
</listitem>
</itemizedlist>
<para>
On Windows, set the property
<code>sun.awt.noerasebackground</code> to reduce flicker. This undocumented property
disables much of the repetitive
background clearing by the AWT implementation. It should be set before any
AWT or Swing components are instantiated.
</para>
<programlisting>
System.setProperty("sun.awt.noerasebackground", "true");
</programlisting>
<note>
<para>
The <code>sun.awt.noerasebackground</code> property is not used on non-Windows platforms.
Reducing resize flicker on those platforms remains an open problem.
</para>
</note>
<para>
Though it is necessary, setting
<code>sun.awt.noerasebackground</code>
has negative consequences. Leaving the background uncleared may result in the
temporary display of previously drawn pixels (an example of what is sometimes called
<ulink url="http://inside-swt.blogspot.com/2006/08/swt-speak-part-1.html">cheese</ulink>)
during resize operations and before the initial Swing contents
are displayed.
</para>
<para>
These effects are removed by adding a resize listener to the parent
SWT composite. When the composite is resized larger, exposing an unpainted
region, the listener fills it immediately with the background color. The
cheese is removed immediately, providing a cosmetic improvement during any delay
while the embedded Swing component repaints.
</para>
<programlisting>
class CleanResizeListener extends ControlAdapter {
private Rectangle oldRect = null;
public void controlResized(ControlEvent e) {
// Prevent garbage from Swing lags during resize. Fill exposed areas
// with background color.
Composite composite = (Composite)e.widget;
Rectangle newRect = composite.getClientArea();
if (oldRect != null) {
int heightDelta = newRect.height - oldRect.height;
int widthDelta = newRect.width - oldRect.width;
if ((heightDelta > 0) || (widthDelta > 0)) {
GC gc = new GC(composite);
try {
gc.fillRectangle(newRect.x, oldRect.height, newRect.width, heightDelta);
gc.fillRectangle(oldRect.width, newRect.y, widthDelta, newRect.height);
} finally {
gc.dispose();
}
}
}
oldRect = newRect;
}
}
</programlisting>
</section>
<section id="sec-tab-traversal">
<title>Tab Traversal</title>
<para>
Another concern of Swing/SWT integration is the behavior of the tab
key when traversing between components from different toolkits.
Additional work is needed on the AWT side of the SWT/AWT
bridge to solve this problem. To achieve proper tab traversal, implement a custom
subclass of <code>java.awt.FocusTraversalPolicy</code> for the embedded AWT frame.
The custom policy may delegate to a standard policy when
tabbing within the frame, but it must transfer control to an SWT
component when:
</para>
<orderedlist>
<listitem>
<simpara>
tabbing on the last component in the frame
</simpara>
</listitem>
<listitem>
<simpara>
back-tabbing on the first component in the frame
</simpara>
</listitem>
</orderedlist>
<para>
Implementing the forward and backward traversals in the custom policy is simple.
However, implementing a proper <code>getDefaultComponent</code> method is tricky. It
must return null when nothing in the embedded AWT frame has focus. This behavior is a hack based on
assumptions about how AWT will call the method, and it is necessary to avoid an immediate
transfer of focus back to AWT after traversing to SWT. For more information, refer to the comments
in the class <code>EmbeddedChildFocusTraversalPolicy</code> in <xref linkend="app-example-code"/>.
</para>
<para>
See the Swing documentation for the
<ulink url="http://java.sun.com/j2se/1.5.0/docs/api/java/awt/doc-files/FocusSpec.html">AWT Focus Subsystem</ulink>
for more information on focus traversal policies.
</para>
</section>
<section id="sec-modality">
<title>Modal Dialogs</title>
<para>
When a
modal dialog is opened from a Swing component, it must be modal across the
entire application. Since SWT and AWT have separate event threads,
such dialogs are not modal by default. The SWT event thread must
be explicitly disabled during the time that a Swing modal dialog is showing.
This effect is most easily achieved by opening a modal SWT dialog while the
Swing dialog is showing.
</para>
<programlisting>
java.awt.Dialog awtDialog = ...
Shell shell = new Shell(parent, SWT.APPLICATION_MODAL | SWT.NO_TRIM);
shell.setSize(0, 0);
shell.addFocusListener(new FocusAdapter() {
public void focusGained(FocusEvent e) {
awtDialog.requestFocus();
awtDialog.toFront();
}
});
</programlisting>
<para>
The 0 x 0 size prevents the shell from being seen. The focus listener makes
sure that control is restored to the Swing dialog if the SWT window somehow gains focus.
(For example, the SWT window may gain focus when the user navigates to your application
through some window managers.)
</para>
<note>
<para>
On Linux/GTK, even a zero-sized SWT dialog may appear as a small dot
on the screen. Hide it by adding the following code to
<code>focusGained()</code>. This addition is unnecessary under Windows and
actually causes a flash, so make the call only when required.
</para>
<programlisting>
shell.moveBelow(null);
</programlisting>
</note>
<para>
The code shown above ensures correct modal behavior, but how should it be invoked?
The easiest approach is to invoke it wherever Swing modal dialogs are created.
However, this solution won't work if your Swing component library cannot be
modified, or if you cannot introduce dependencies on SWT code from
the Swing component library.
</para>
<para>
Alternatively, correct modal behavior is enforced more cleanly by installing a listener for all AWT
window events. Whenever it is detected that a Swing modal dialog is open or visible, a
SWT modal dialog must be opened. The listener is sketched below and is
fully implemented in the example code. See <xref linkend="app-example-code"/> for more
information.
</para>
<programlisting>
class AwtDialogListener implements AWTEventListener, ComponentListener {
private final Display display;
AwtDialogListener(Display display) {
this.display = display;
Toolkit.getDefaultToolkit().addAWTEventListener(this, AWTEvent.WINDOW_EVENT_MASK);
}
private void handleRemovedDialog(Dialog awtDialog, boolean removeListener) {
// An AWT dialog has been closed or set invisible. Close the SWT dialog
...
}
private void handleAddedDialog(final Dialog awtDialog) {
// An AWT dialog has been opened or set visible. Open the SWT dialog
// and add this as a component listener on the dialog to catch
// visibility changes
...
}
private void handleOpenedWindow(WindowEvent event) {
Window window = event.getWindow();
if (window instanceof Dialog) {
handleAddedDialog((Dialog)window);
}
}
private void handleClosedWindow(WindowEvent event) {
// Dispose-based close
Window window = event.getWindow();
if (window instanceof Dialog) {
// Remove dialog and component listener
handleRemovedDialog((Dialog)window, true);
}
}
private void handleClosingWindow(WindowEvent event) {
// System-based close
// (see example code for full implementation)
...
}
public void eventDispatched(AWTEvent event) {
switch (event.getID()) {
case WindowEvent.WINDOW_OPENED:
handleOpenedWindow((WindowEvent)event);
break;
case WindowEvent.WINDOW_CLOSED:
handleClosedWindow((WindowEvent)event);
break;
case WindowEvent.WINDOW_CLOSING:
handleClosingWindow((WindowEvent)event);
break;
default:
break;
}
}
public void componentHidden(ComponentEvent e) {
Object obj = e.getSource();
if (obj instanceof Dialog) {
// Remove dialog but keep listener in place so that we know if/when it is set visible
handleRemovedDialog((Dialog)obj, false);
}
}
public void componentShown(ComponentEvent e) {
Object obj = e.getSource();
if (obj instanceof Dialog) {
handleAddedDialog((Dialog)obj);
}
}
...
}
</programlisting>
</section>
<section id="sec-dismissing-popups">
<title>Dismissing Pop-up Menus</title>
<para>
When a context menu is displayed in an embedded AWT frame, the menu does not
disappear after clicking outside the frame. This AWT limitation is well known,
but it is especially noticeable in embedded frames since it may result in
multiple visible pop-ups within the same SWT shell.
</para>
<figure id="fig-double-popup">
<title>Double Popups</title>
<mediaobject>
<imageobject>
<imagedata fileref="images/double-popup.jpg"/>
</imageobject>
</mediaobject>
</figure>
<para>
This issue is documented in Sun bugs
<ulink url="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4311449">4311449</ulink>
and <ulink url="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4290715">4290715</ulink>,
among others.
</para>
<para>There are partial workarounds to this problem:</para>
<itemizedlist>
<listitem>
<para>
<emphasis>Manually dismiss Swing pop-ups when the user activates other windows.</emphasis> Install a
listener for window focus events on the embedded frame. On a focus lost event, the window
and component hierarchies of the frame can be searched for instances of
<code>javax.swing.JPopupMenu</code>.
<note>
<para>
This workaround applies to JRE version 1.4 and earlier; it should not be
necessary if you are using version 1.5 or later.
</para>
</note>
</para>
</listitem>
<listitem>
<para>
<emphasis>Manually dismiss Swing pop-ups when the user activates an SWT menu.</emphasis> Install
a display filter to listen for <code>SWT.Show</code> events which are generated whenever an
SWT menu is shown. In the filter's event handler, visible Swing pop-ups can be dismissed as described
above.
</para>
</listitem>
</itemizedlist>
<para>
Despite these workarounds, some issues remain; for example, Swing pop-ups are not
dismissed when the user interacts with the titlebar on the workbench window.
</para>
</section>
<section id="sec-system-settings">
<title>Synchronizing with System Settings</title>
<para>
When the user changes font settings through the Windows control panel, the
changes are not always properly propagated to Swing components. This problem is
especially noticeable when integrating with SWT since the SWT components do, in fact,
recognize these changes. To work around the problem, manually
change the font in the Swing Windows Look and Feel when the system font has changed.
</para>
<para>
Fortunately, in Eclipse 3.2, a new SWT event has been added to allow applications
to detect changes to system settings. So, Swing font changes can be triggered
as follows
</para>
<programlisting>
Display display = ...
Listener settingsListener = new Listener() {
public void handleEvent(Event event) {
handleSettingsChange();
}
};
display.addListener(SWT.Settings, settingsListener);
</programlisting>
<para>
Font changes for Swing components are best handled through the
look and feel, rather than updating the font for individual components.
</para>
<programlisting>
private void handleSettingsChange() {
...
org.eclipse.swt.graphics.Font currentSystemFont = ...;
FontData fontData = currentSystemFont.getFontData()[0];
int resolution = Toolkit.getDefaultToolkit().getScreenResolution();
int awtFontSize = (int)Math.round((double)fontData.getHeight() * resolution / 72.0);
// The style constants for SWT and AWT map exactly, and since they are int constants, they should
// never change. So, the SWT style is passed through as the AWT style.
java.awt.Font awtFont = new java.awt.Font(fontData.getName(), fontData.getStyle(), awtFontSize);
FontUIResource fontResource = new FontUIResource(awtFont);
UIManager.put("Button.font", fontResource);
UIManager.put("CheckBox.font", fontResource);
UIManager.put("ComboBox.font", fontResource);
... // many more similar calls
Container contentPane = ... // content pane from the root pane
SwingUtilities.updateComponentTreeUI(contentPane);
}
}
</programlisting>
<para>
First, the SWT font is converted to an equivalent AWT font.
AWT font sizes always assume a 72 dpi resolution. The true screen resolution must be
used to convert the platform font size into an AWT point size that matches when displayed.
Then, the font for various Swing component types is changed via the look and feel's
<code>javax.swing.UIManager</code>.
</para>
<para>
See the example code (<xref linkend="app-example-code"/>) for the complete implementation.
</para>
</section>
<section id="sec-keystroke-contention">
<title>Keystroke Contention</title>
<para>
Unexpected results can occur if you map the same keystroke to a global action
in your RCP application and to a handler in an embedded Swing component.
Keystrokes defined through the <code><ulink url="http://help.eclipse.org/help32/index.jsp?topic=/org.eclipse.platform.doc.isv/reference/extension-points/org_eclipse_ui_bindings.html">
org.eclipse.ui.bindings</ulink></code> extension point will take precedence over those
defined in the Swing component, even if the Swing component has focus. In this case, the
RCP binding is managed through a Display filter, so the keystroke is consumed before
it reaches the Swing component at all. As a result, there is no simple, general
workaround to avoid this problem at the level of the embedded composite. Instead, you
can avoid these conflicts by:
<itemizedlist>
<listitem>
<para>
Using the <code><ulink url="http://help.eclipse.org/help32/index.jsp?topic=/org.eclipse.platform.doc.isv/reference/extension-points/org_eclipse_ui_contexts.html">
org.eclipse.ui.contexts</ulink></code> extension point to organize key bindings that should
not be visible when the Swing component is in focus.
</para>
</listitem>
<listitem>
<para>
Replicate the Swing component's action in an RCP action, bound to the same keystroke. The
binding for RCP action can be introduced through an <code>org.eclipse.ui.contexts</code>
extension. The action can be implemented to invoke the underlying the Swing action. This
approach may be necessary anyway, if you want the action to be available anywhere outside
the Swing component (for example, in the application's main menu).
</para>
</listitem>
</itemizedlist>
</para>
<para>
There are also occasional issues with keystroke contention between the embedded Swing
component and the window system. For example, hitting Shift-F10 from inside many Swing
components opens a context (popup) menu. In Windows, when there is no context menu, the default
processing of the F10 keystroke
(with or without shifting) transfers focus to the application's main menu bar.
When you have embedded Swing components, these two behaviors conflict.
The Swing component properly handles Shift-F10, showing the popup, but the containing SWT shell does
not know it; therefore, it reports the keystroke to Windows as unhandled. Windows then
transfers focus to the main menu bar, and the popup loses focus.
</para>
<para>
Fortunately, this conflict can be resolved. Here's some code which exploits the fact that
the default Windows behavior happens when F10 is released, rather than when it is pressed.
The embedded composite can install a KeyListener and consume the release of the
Shift-F10 keystroke so that Windows never sees it.
</para>
<programlisting>
public void keyReleased(KeyEvent e) {
if (e.keyCode == SWT.F10 &amp;&amp; (e.stateMask &amp; SWT.SHIFT) != 0) {
e.doit = false;
}
}
</programlisting>
</section>
<section id="sec-other-workarounds">
<title>Other Workarounds</title>
<para>
Due to Sun bug <ulink url="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6411042">6411042</ulink>,
when AWT/Swing components are
added to an embedded frame from the SWT event thread, a memory leak occurs. To
avoid the leak, it is best to create and add these components from the AWT event thread
instead. Simply invoke the creation code through
<code>javax.swing.SwingUtilities.invokeLater()</code>.
As discussed earlier, it is a good general habit to call Swing APIs from the
AWT event thread anyway.
</para>
</section>
</section>
<section id="sec-unresolved-issues">
<title>Unresolved Issues</title>
<section id="sec-cleartype">
<title>ClearType</title>
<para>
On Windows under JRE 1.5 and earlier, the Swing system look and feel does not
seamlessly support <ulink url="http://www.microsoft.com/typography/ClearTypeInfo.mspx">ClearType</ulink>
anti-aliasing. By default, when ClearType is enabled and the same font and font
size are chosen for Swing and SWT controls, the fonts appear to be different. A
partial solution is available through setting the
property <code>swing.aatext</code> to "true". This undocumented property enables font anti-aliasing
in pre-Java 6 environments, but it simply turns anti-aliasing on. It does not synchronize with current
Windows system settings. Also, Swing has its own anti-aliasing algorithm, so
minor differences from natively-displayed fonts remain visible.
</para>
<para>
This problem has been <ulink url="http://weblogs.java.net/blog/chet/archive/2005/06/phils_font_fixe.html">resolved</ulink>
in Java 6 (see bugs <ulink url="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4726365">4726365</ulink>
and <ulink url="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4871297">4871297</ulink>
for more information).
</para>
<para>
Below is a screenshot which illustrates the problem. Here, two SWT-based views are on
the left, and a Swing table component is on the right.
</para>
<figure id="fig-cleartype">
<title>Font Differences with ClearType</title>
<mediaobject>
<imageobject>
<imagedata fileref="images/cleartype.jpg"/>
</imageobject>
</mediaobject>
</figure>
</section>
<section id="sec-cursor-synchronization">
<title>Cursor Synchronization</title>
<para>
SWT cursor changes are not reflected in embedded Swing components. The SWT cursor
changes back to the default arrow cursor as the mouse moves over the embedded frame.
</para>
<para>
A solution to this problem may now be possible. As of Eclipse 3.3, new API is
available to query the current cursor (see bug
<ulink url="https://bugs.eclipse.org/bugs/show_bug.cgi?id=133943">133943</ulink>
).
</para>
</section>
</section>
<section id="sec-conclusion">
<title>Conclusion</title>
<para>
Smooth integration of Swing components into an RCP application is possible. It requires
more than the SWT/AWT Bridge, however. You can implement the techniques described above
in a modular fashion to improve the behavior of the SWT/AWT Bridge for
real-world applications. <xref linkend="app-example-code"/> contains example
code that demonstrates all of these additional practices.
</para>
</section>
<bibliography id="bin-resources">
<title>Resources</title>
<biblioentry id="bib-example-code">
<bibliosource><ulink url="files/swingintegration.example_0.0.2.jar">Example Code</ulink></bibliosource>
</biblioentry>
<biblioentry id="bib-bridge">
<bibliosource>
<ulink
url="http://help.eclipse.org/help32/topic/org.eclipse.platform.doc.isv/reference/api/org/eclipse/swt/awt/package-summary.html">
SWT/AWT Bridge Javadoc
</ulink>
</bibliosource>
</biblioentry>
<biblioentry id="bib-look-and-feel">
<bibliosource>
<ulink
url="http://java.sun.com/docs/books/tutorial/ui/features/plaf.html">
Java Look and Feel Information
</ulink>
</bibliosource>
</biblioentry>
<biblioentry id="bib-root-pane">
<bibliosource>
<ulink
url="http://java.sun.com/j2se/1.5.0/docs/api/javax/swing/JRootPane.html">
Swing Root Pane Documentation
</ulink>
</bibliosource>
</biblioentry>
<biblioentry id="bib-awt-focus">
<bibliosource>
<ulink url="http://java.sun.com/j2se/1.5.0/docs/api/java/awt/doc-files/FocusSpec.html">AWT Focus Subsystem</ulink>
</bibliosource>
</biblioentry>
</bibliography>
<appendix id="app-example-code">
<title>Example Code</title>
<para>
The ideas for improving Swing/SWT integration presented in
<xref linkend="sec-adding-to-bridge"/> have been collected into a full
example implementation <xref linkend="bib-example-code"/>. The example
includes an API that is used to create embedded Swing components
simply and cleanly. The example code requires SWT version 3.2 or higher.
</para>
<para>
Import the example with "File -> Import...", selecting "Plug-ins and Fragments". Import the
plug-in as "Projects with Source Folders". Make sure that your
compiler settings specify a source compatibility version of at least 1.4 (Preferences -> Java -> Compiler).
Otherwise the <code>assert</code> statements in the example code will not compile.
</para>
<para>
<ulink url="files/example-javadoc/index.html">Javadoc</ulink>
is available for the API. To embed Swing components, refer to
the javadoc for
<code>
<ulink
url="files/example-javadoc/swingintegration/example/EmbeddedSwingComposite.html">
EmbeddedSwingComposite</ulink></code>. To display Swing dialogs without embedding, refer to the javadoc for
<code>
<ulink url="files/example-javadoc/swingintegration/example/AwtEnvironment.html">
AwtEnvironment</ulink></code>.
</para>
</appendix>
</article>