6 swt programming

SWT (Standard Widget
Toolkit) TUTORIAL
By Kalman Hazins
(kalman@zikal.com)

Agenda
 Brief History of Java GUI
 Installing SWT
 Creating widgets
 SWT Layouts
 Event Handling
 Sample Application

History of Java GUI
 AWT – Abstract Windowing Toolkit
 First released in 1995 as part of JDK 1.0 by Sun
 Heavyweight GUI components – a Java component creates a peer
component on the operating system and the peer draws itself.
 Least Common Denominator problem – for simple GUI components
creating a peer works, what about the components that are only
available on some platforms and not others? If you want to write code
that’s truly portable – you have to use components that are available on
all platforms
 The logic makes sense – but how do you develop a serious application
using just the basic components (available on all platforms)?
 You don’t …
 Enter Swing

History of Java GUI (Cont.)
 Swing (JFC – Java Foundation Classes)
 Released in 1998 as part of JDK 1.1
 Lightweight GUI components – no need for operating system
“peer”-based drawing. Let’s draw the components ourselves.
Lightweight – there is no actual weight (operating system
component) behind the Java component.
 Nice toolkit with enhanced Model-View-Controller architecture
and superior graphics 2D library.
 Portable? You bet. Any problems? Now that you are not actually
using the operating system components – you are just mimicking
the behavior of the operating system. Hence, the look and feel
as well as the response speed are not the same.
 Swing got much better over time
 Still, very few commercial applications are written in Swing.

History of Java GUI (Cont.)
 SWT (Standard Widget Toolkit)
 GUI toolkit released in November 2001
 Was initially designed to write the now extremely famous and
popular Eclipse IDE
 “Best of both worlds” approach – use native functionality when
available, and Java implementation when unavailable
 Takes on the appearance and behavior of the native platform
 Because of its close bond with the operating system, SWT
needs to be ported separately for every platform
 Currently, implementations of SWT are already available for all
major desktop operating systems and some handheld devices
 The code YOU write will be portable for all the platforms that
have SWT implementations for them (unless you decide to do
some platform specific stuff like OLE on windows)
 http://www.eclipse.org/swt/ - SWT home page

Installing SWT
 To compile and run SWT applications you need
1. SWT jars (usually just swt.jar)
2. SWT native libraries
 Detailed Instructions on obtaining and “installing”
1. Go to http://www.eclipse.org/swt and follow one of the many
mirror links
2. This will bring you to another page, where you want to follow the
“Latest Release” link
3. This should bring you to a page which will say “Release Build: “ in
bold letters on the very top
4. Scroll down to the bottom of the page till you see “SWT Binary and
Source” section
5. Pick the platform you intend to develop on from the list (e.g.
Windows XP) and click on “(http)” to start downloading the zip file
6. Extract the contents of the zip file into a directory and you are
ready for the final step(s) (let’s say our directory path is C:SWT)

Installing SWT (Cont.)
7. You need to include swt.jar (and possibly other jars) from the C:SWT
folder in your classpath (for an example on setting classpath see
http://www.moreservlets.com/Using-Tomcat-4.html#Set-CLASSPATH)
8. You also need to include the native library files (e.g. *.dll) from
C:SWT in your java.library.path.
a. The easiest way to do this one is to execute the following
command from a regular java program
System.out.println(System.getProperty(“java.library.path”));
which will give you a list of the directories in your “library path”.
You can then copy the native library files from C:SWT to one of
those directories.
-OR-
b. Simply provide the path when running java
java –Djava.library.path=C:SWT classname

Creating Widgets
 SWT Javadoc - http://www.jlab.net/eclipse/doc/3.1/index.html
 Simplest SWT program (explained over the next few slides)
1. import org.eclipse.swt.widgets.*;
2. import org.eclipse.swt.widgets.Shell;
3. public class HelloWorld {
4. public static void main(String[] args) {
5. Display display = new Display();
6. Shell shell = new Shell(display);
7. shell.setText("Hello World");
8. shell.setSize(250, 100);
9.
10. shell.open();
11.
12. while (!shell.isDisposed()) {
13. if (!display.readAndDispatch()) {
14. display.sleep();
15. }
16. }
17. display.dispose();
18. }
19. }

Creating Widgets (Cont.)
 Think of Shell object (line 6) being almost the same as a JFrame in
Swing, i.e. the highest-level container, which contains other widgets (e.g.
buttons, labels etc.) inside of it
 Unlike Swing
1. You need to create Display object (line 5), which represents the
underlying windowing system. This in turn serves as a parent to the
Shell. (In SWT, every widget you create will always have its parent
passed into the widget’s constructor.)
2. You need to keep the Shell open to listen for events with a while loop
(lines 12-16). Otherwise, the Shell will immediately close itself.
3. Since you are not just writing some Java code (having the luxury of
garbage collector clean up after you), but are actually requesting some
heavyweight resources from the underlying platform – you need to
dispose of those resources when you are done with them(line 17).
(Luckily, disposing of the parent disposes of its child, so 99% of time you
will not be running around disposing of widgets right and left.)
 If you are a Swing guy, and the above 3 things greatly bother you – you
can write a simple SWTUtil class to help you deal with it …

Homegrown SWT Utility
 SWTUtil.java
import org.eclipse.swt.widgets.*;
public class SWTUtil {
private static Display display = new Display();
public static Shell getShell() {
Shell shell = new Shell(display);
return shell;
}
public static void openShell(Shell shell) {
shell.open();
// This loop keeps the shell open constantly listening for events
while (!shell.isDisposed()) {
if (!display.readAndDispatch()) {
display.sleep();
}
}
display.dispose();
}
}

SWT Utility in Action
 “Simplest SWT program” rewritten
using SWTUtil class
import org.eclipse.swt.widgets.*;
public class HelloWorld {
public static void main(String[] args) {
Shell shell = SWTUtil.getShell();
shell.setText(“Still Hello World");
shell.setSize(250, 100);
SWTUtil.openShell(shell);
}
}

Widget creation explained
 A widget in SWT is created by
1. Specifying parent
2. Specifying style
 A parent is the container that the widget is created inside of (e.g.
Shell).
 Style is any constant from the SWT class (SWT.PUSH,
SWT.BORDER, SWT.LEFT etc).
 All styles applicable to the widget can be found in the Javadoc for
that widget (as well as its superclasses if any).
 If more than one style is desired – separate them out with a “|”
bitwise operator (e.g. SWT.MULTI |
SWT.V_SCROLL|SWT.H_SCROLL| SWT.BORDER creates a multiline
textarea that has vertical and horizontal scrollbars and a border
around it). If no specific style is desired – use SWT.NONE. The style
you are requesting is only a hint, so if the underlying platform
doesn’t support it – you are out of luck.

Label
 Unselectable, uneditable text
 SWT.VERTICAL or SWT.HORIZONTAL can be used together with
SWT.SEPARATOR to create a label that is a horizontal/vertical separator
 LabelWorld.java
1. import org.eclipse.swt.SWT;
2. import org.eclipse.swt.layout.GridLayout;
4. public class LabelWorld {
6. Shell shell = SWTUtil.getShell();
7. shell.setText("Label World");
8. shell.setLayout(new GridLayout()); // layouts are explained later
9.
10. // Create labels
11. new Label(shell, SWT.NONE).setText("Regular label");
12. new Label(shell, SWT.SEPARATOR);
13. new Label(shell, SWT.SEPARATOR|SWT.HORIZONTAL);
14.
15. // pack and show
16. shell.pack();
17. SWTUtil.openShell(shell);
18. }
19. }

Button
 Once a button – always a button. All types of buttons are created using the Button
class. Push buttons, radio buttons, check buttons, toggle buttons and even flat
buttons.
 ButtonWorld.java
4. public class ButtonWorld {
7. shell.setText("Button World");
8. shell.setLayout(new GridLayout(2, true)); // layouts are explained later
9.
10. new Button(shell, SWT.PUSH | SWT.FLAT).setText("Flat Push Button");
11. new Button(shell, SWT.CHECK).setText("Check Button");
12. new Button(shell, SWT.TOGGLE).setText("Toggle Button");
13. new Button(shell, SWT.RADIO).setText("Radio Button");
14.
16. shell.pack();
18. }
19. }

Text
 Different types of text widgets are created using Text class by providing the
appropriate styles
 TextWorld.java
4. public class TextWorld {
7. shell.setText("Text World");
9.
10. new Text(shell, SWT.NONE).setText("Missing something ...");
11. new Text(shell, SWT.BORDER); // regular textfield
12. new Text(shell, SWT.PASSWORD | SWT.BORDER).setText("password");
13. new Text(shell, SWT.READ_ONLY | SWT.BORDER).setText("Can't type inside");
14. new Text(shell, SWT.MULTI | SWT.V_SCROLL | SWT.WRAP
15. | SWT.BORDER).setText("nnn");
16.
18. shell.pack();
20. }
21. }

List
 Pick from a list – single or multiple selection available
 ListWorld.java
4. public class ListWorld {
7. shell.setText("List World");
9.
10. String[] items = "One Two Three Four Five Six".split(" ");
11. List one = new List(shell, SWT.SINGLE | SWT.BORDER);
12. one.setItems(items);
13. one.select(2);
14. List two = new List(shell, SWT.MULTI | SWT.BORDER);
15. two.setItems(items);
16. two.setSelection(items);
17.
19. shell.pack();
21. }
22. }

Combo
 Benefits of both Text and List widgets in one!
 ComboWorld.java
4. public class ComboWorld {
7. shell.setText("Combo World");
9.
10. String[] items = "One Two Three Four Five Six".split(" ");
11. Combo one = new Combo(shell, SWT.DROP_DOWN);
12. one.setItems(items);
13. Combo two = new Combo(shell, SWT.DROP_DOWN | SWT.READ_ONLY);
14. two.setItems(items);
15. Combo three = new Combo(shell, SWT.SIMPLE);
16. three.setItems(items);
17.
19. shell.pack();
21. }
22. }

Group
 Used to group widgets together. (Very similar to JPanel in Swing)
 GroupWorld.java
4. public class GroupWorld {
7. shell.setText("Group World");
9.
10. Group buttonGroup = new Group(shell, SWT.SHADOW_OUT);
11. buttonGroup.setText("Six buttons");
12. buttonGroup.setLayout(new GridLayout(3, true));
13. for(int i = 0; i < 6; i++) {
14. new Button(buttonGroup, SWT.RADIO).setText("Bottle " + (i + 1));
15. }
16.
18. shell.pack();
20. }
21. }

Browser
 One of the newer widgets of SWT for displaying web content.
 Cool stuff!!! (See the sample application later)
 BrowserWorld.java
2. import org.eclipse.swt.browser.Browser;
3. import org.eclipse.swt.layout.FillLayout;
4. import org.eclipse.swt.widgets.Shell;
5. public class BrowserWorld {
8. shell.setText("Browser World");
9. shell.setLayout(new FillLayout());
10.
11. Browser browser = new Browser(shell, SWT.BORDER);
12. browser.setSize(900, 500);
13. browser.setUrl("http://www.eclipse.org/swt/");
14.
16. shell.pack();
18. }
19. }

SWT Layouts
 Layouts first introduced in AWT
 Ease burden of laying out components
 Promote cross-platform GUI design
 SWT offers 5 layouts:
1. FillLayout
2. RowLayout
3. StackLayout
4. GridLayout
5. FormLayout
 You set the composite’s layout by calling setLayout()
 You don’t have to use a layout, but do you really want your widgets to
disappear when the user resizes the window?
 More on layouts
http://www.eclipse.org/articles/Understanding%20Layouts/Understanding%20Layouts.htm

FillLayout
 Places all widgets in either a single column or a single row depending on if
SWT.VERTICAL or SWT.HORIZONTAL is used
 Makes all widgets the same size
 FillLayoutExample.java
2. import org.eclipse.swt.layout.FillLayout;
4. public class FillLayoutExample {
7. shell.setText("FillLayoutExample");
8. shell.setLayout(new FillLayout(SWT.HORIZONTAL));
9.
10. for(int i = 0; i < 3; i ++) {
11. new Button(shell, (i % 2 == 0) ? SWT.RADIO : SWT.PUSH).setText("Button " + i);
12. new Text(shell, SWT.BORDER).setText("same size");
13. }
14.
16. shell.pack();
18. }
19. }

RowLayout
 Similar to FillLayout - places all widgets in either a single column or a single row depending on if SWT.VERTICAL
or SWT.HORIZONTAL is used
 Doesn’t force all widgets to be the same size
 Can wrap to a new row or column if it runs out of space
 Can use RowData objects to determine initial heights/widths for controls
 RowLayoutExample.java
2. import org.eclipse.swt.layout.RowData;
3. import org.eclipse.swt.layout.RowLayout;
5. public class RowLayoutExample {
8. shell.setText("RowLayoutExample");
9. shell.setLayout(new RowLayout(SWT.HORIZONTAL));
10.
11. for(int i = 0; i < 3; i ++) {
12. new Button(shell, (i % 2 == 0) ? SWT.RADIO : SWT.PUSH).setText("Button " + i);
13. new Text(shell, SWT.BORDER).setLayoutData(new RowData(5, 50));
14. }
15.
17. shell.pack();
19. }
20. }

StackLayout
 Similar to CardLayout in Swing. The basic idea is that all widgets are stacked on top of each other and you can
only see one at a time.
 Need to set topControl attribute for the layout to show any widget on top
 Need to call layout() on the Composite every time you reassign topControl
 StackLayoutExample.java
2. import org.eclipse.swt.custom.StackLayout;
3. import org.eclipse.swt.events.*;
5. public class StackLayoutExample {
7. final Shell shell = SWTUtil.getShell();
8. shell.setText("RowLayoutExample");
9. shell.setLayout(new StackLayout());
10.
11. final Button button1 = new Button(shell, SWT.PUSH);
12. button1.setText("Button One");
13. final Button button2 = new Button(shell, SWT.PUSH);
14. button2.setText("Button Two");
15. class StackLayoutAdapter extends SelectionAdapter {
16. public void widgetSelected(SelectionEvent event) {
17. ((StackLayout)shell.getLayout()).topControl =
18. (event.widget == button1) ? button2 : button1;
19. shell.layout();
20. }
21. }
22. button1.addSelectionListener(new StackLayoutAdapter());
23. button2.addSelectionListener(new StackLayoutAdapter());
24.
25. ((StackLayout)shell.getLayout()).topControl = button1;
26. shell.pack();
28. }
29. }


GridLayout
 Lays out controls in a grid.
 A lot of people love this powerful layout.
 You can easily specify what you want to happen when the composite is
resized
 6 attributes (defaults are preset):
1. int horizontalSpacing – horizontal space in pixels between
adjacent cells
2. int verticalSpacing – vertical space in pixels between adjacent
cells
3. boolean makeColumnsEqualWidth – forces all columns to be
same width
4. int marginWidth – margin in pixels along right and left edges
5. int marginHeight – margin in pixels along top and bottom edges
6. int numColumns – number of columns for the layout
 GridLayout(int numColumns, boolean makeColumnsEqualWidth)
 Uses GridData objects to provide for better control
 Too many options to list …
 Warning for Swing programmers – DO NOT TRY TO REUSE GridData
objects
 Instead, you need to create a new GridData object for every widget that
needs non-default behavior

GridLayoutExample.java
2. import org.eclipse.swt.layout.*;
4. public class GridLayoutExample {
7. shell.setText("GridLayoutExample");
8. shell.setLayout(new GridLayout(2, false)); // 2 columns, same width
9.
10. // Username
11. new Label(shell, SWT.RIGHT).setText("Username:");
12. Combo cmbUsername = new Combo(shell, SWT.DROP_DOWN);
13. cmbUsername.setLayoutData(new GridData(GridData.FILL_HORIZONTAL));
14. cmbUsername.setItems(new String[]{"Howard", "Admin", "Kalman"});
15. cmbUsername.setText("Admin");
16.
17. // Password
18. new Label(shell, SWT.RIGHT).setText("Password:");
19. new Text(shell, SWT.BORDER | SWT.PASSWORD).GridData(GridData.FILL_HORIZONTAL));
20.
21. // Login Button
22. Button loginButton = new Button(shell, SWT.PUSH | SWT.FLAT);
23. loginButton.setText("Proceed to your account");
24. GridData data = new GridData(GridData.FILL_HORIZONTAL);
25. data.horizontalSpan = 2; // span 2 columns
26. loginButton.setLayoutData(data);
27. shell.pack();
29. }
30. }

FormLayout
 Considered the most complex layout of SWT
 Based on y = ax + b (not that most people who use it care)
 MAXIMUM flexibility
 People who understand it – love it 
 The basic idea is that you layout the widgets relative to each other or to the enclosing
composite
 Needs a tutorial of its own and is therefore not covered here …

Event Handling
 If you are familiar with Swing – this last part should be a joke.
 SWT widgets can listen for events to happen.
 If you would like to hear when and what they hear – you need to attach a listener to
the widget
 Listener is basically an interface that defines when certain behaviors happen
 Sometimes, listener tries listening out for two many things, but you only care to listen
for one particular event
 In such a case – you need an adapter. Adapter is a class that implements the
interface and from which you can just extend and override the method you are
interested in.
 Some of the popular listeners/adapters are listed below
 FocusListener/FocusAdapter – listens for focus gained and focus lost events
 KeyListener/KeyAdapter – listens for key releases and key presses
 ModifyListener(only has 1 method) – listens for text modifications
 VerifyListener – listens for (and potentially intercepts) text modifications
 MouseListener/MouseAdapter – listens for mouse button presses
 SelectionListener/SelectionAdapter – listens for selection events (similar to
ActionListener in Swing)

EventHandling.java
2. import org.eclipse.swt.events.*;
3. import org.eclipse.swt.layout.*;
5. public class EventHandling {
6. private static boolean numbersOnly;
9. shell.setText("EventHandling");
10. shell.setLayout(new GridLayout(2, false));
11.
12. // input
13. Label lblInput = new Label(shell, SWT.RIGHT);
14. lblInput.setText("Type in here:");
15. GridData data = new GridData(GridData.HORIZONTAL_ALIGN_END);
16. lblInput.setLayoutData(data);
17. Text input = new Text(shell, SWT.BORDER);
18. input.addVerifyListener(new VerifyListener() {
19. public void verifyText(VerifyEvent vEvent) {
20. vEvent.doit = false; // don't allow anything but numbers
21. if(!numbersOnly || vEvent.character == 'b') {
22. vEvent.doit = true;
23. }
24. else if(Character.isDigit(vEvent.character) && numbersOnly) {
25. vEvent.doit = true;
26. }
27. }
28. });

EventHandling.java
29. Button btnAllow = new Button(shell, SWT.CHECK);
30. btnAllow.setText("Allow numbers only");
31. data = new GridData(GridData.HORIZONTAL_ALIGN_CENTER);
32. data.horizontalSpan = 2;
33. btnAllow.setLayoutData(data);
34. btnAllow.addSelectionListener(new SelectionAdapter() {
35. public void widgetSelected(SelectionEvent selectionEvent) {
36. numbersOnly = ((Button)(selectionEvent.widget)).getSelection();
37. }
38. });
39. shell.pack();
41. }
42. }

syncExec() / asyncExec()
 You should only be updating user interfaces from the user interface thread.
 For example, say you create a Label in your main thread. Then, you have a separate thread that
does some sort of a long computation. Then, you want to update your label with the result of the
second thread’s computation. You CANNOT just call label.setText(newValue) in your second
thread.
 Instead, you have to call either syncExec(Runnable) or asyncExec(Runnable) methods on the
instance of Display
// Say you run a thread that calculates new time approximately every second
// and tries to update a label
new Thread(new Runnable() {
public void run() {
Display display = shell.getDisplay();
while(!shell.isDisposed()) {
try {
display.asyncExec(new Runnable() {
public void run() {
clock.setText((new Date()).toString());
}
});
Thread.sleep(1000);
}
catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}).start();

Sample Application
 Goal: Write a cute browser in SWT (under
300 lines) that handles most HTML
 CuteBrowser.java uses SWTUtil.java
 Run the application on Windows XP
computer that has java installed

6 swt programming

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