Eclipse SWT development
Working With Standard Widget Toolkit
Standard Widget Toolkit (SWT) is the foundation on which entire Eclipse
UI is based. SWT provides easy to use widgets and API's which are
helpful in building rich user interfaces. SWT is designed in a way so as
to give us access to the underlying operation system resources. It uses
native (OS) widgets which gives an native look and feel, similar to what
is provided by operating system (See figures below). SWT includes many
different type of controls for ex: tree, table, button, label etc. This
tutorial introduces SWT by describing some of the basic concepts and
classes.
  
SWT Widgets
SWT provides a rich set of widgets that can be used to create either
stand-alone Java applications or Eclipse plug-ins. We will start by
implementing a small SWT example before getting into details about each
of the widgets you are likely to use. In order to create this standalone
version of swt
program we will start by creating new java Project in eclipse.
Before you can start using SWT, the SWT libraries need to be added to
your project's classpath. To add SWT support, do the following:
1. Download SWT library. For 3.1.2 version of eclipse, SWT library is
available at
http://archive.eclipse.org/eclipse/downloads/drops/R-3.1.2-200601181600/index.php
Look for the section titled SWT Binary and Source.
2. From main menu tool bar, select "File" followed by "Import". Doing so
will bring up the "Import wizard" dialog.
3. Now select "Existing Projects into Workspace" and click on "Next"
button.
4. Click on "Select archive file" followed by "Browse" button. Now
locate the SWT archive that you downloaded in step 1.
5. Click the Finish button to finish importing the SWT project into your
workspace.
6. Create new java project from File > New Java Project.
7. Right-click on the project and select the Properties command to open
the Properties dialog.
8. Select the Java Build Path followed by Projects tab and click the Add
button.
9. Select the org.eclipse.swt project and click OK to finish adding the
SWT libraries to your project's classpath
Create a new Standalone SWT Program
Create a new java class
as follows:
1 import org.eclipse.swt.*;
2 import org.eclipse.swt.graphics.*;
3 import org.eclipse.swt.widgets.*;
4 public class FirstExample {
5 public static void main(String[] args){
6 Display firstDisplay = new Display();
7 Shell firstShell = new Shell(firstDisplay);
8 firstShell.setText("First Example");
9 firstShell.setSize(200,100);
10 firstShell.open ();
11 while (!firstShell.isDisposed()) {
12 if (!firstDisplay.readAndDispatch())
13 firstDisplay.sleep ();
14 }
15 firstDisplay.dispose ();
16 }
17 }
Lines 1-3: SWT classes are contained in different packages which begin
with org.eclipse.swt. The package org.eclipse.swt is the main package
and contains SWT class and exception/error classes. All the SWT widgets
are contained in org.eclipse.swt.widgets package. Refer to online help
for more information about these packages
Line 6: Every SWT program has a Display. Display acts like a bridge
between program and underlying operating system
Lines 7-9: Next, in the program we have created a shell. All the Top
level windows are created by the class Shell and shell's are contained
in Display.
Line 10: When a shell is created it is invisible by default. Shell
becomes visible only when method open() is called on shell instance.
open() method not only makes shell visible but also brings it to the
front so that all user input can be intercepted by the shell.
Lines 11-14: SWT supports an event based user interface. Event driven
user interface essentially means that user interaction events are
generated which are then intercepted by eclipse application to perform
various actions. Not surprisingly, any event driven UI requires an event
loop that continously listens to user interface events and then
broadcasts the events to interested parties. Example of such event could
be "Button click", "Minimize Window" etc. The condition when this event
loop ends depend upon the application For ex: in some cases user might
close the window OR clicks on the exit button provided by the
application.
Line 15: Next, we are disposing the Display. Disposing display will
release all resources that were acquired by the running program in its
lifetime.
In order to run this example program use the Run As > "SWT Application".
This will open up new window with title “First Example”.
Events
As discussed earlier, SWT supports an event based user interface. These
events are generated by user actions. User actions could be keyboard
entry, button click, mouse drag etc. We can trap or listen to these
events by adding/attaching listeners to various SWT controls. Following
listing shows an example to attach selection listener to button widget
final Button myButton = new Button(shell, SWT.PUSH);
SelectionAdapter adapter = new SelectionAdapter() {
public void widgetSelected(SelectionEvent event) {
myButton.setText("You clicked me!");
}
};
myButton.addSelectionListener(adapter);
myButton.setText("Click");
For complete listing of events, listeners refer to online
help
In order to know more about events and widgets which support each of
these events refer to online
Platform Plug-in Developer Guide. Look for
headings Low level events and High level events.
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