SWT: Add event handler to button

Event handlers are used to get notification when particular events happened on SWT widget.

Ex:

button1.addSelectionListener(new SelectionAdapter() {

         public void widgetSelected(SelectionEvent e) {

                 System.out.println("Submit button was clicked");

         }

});

By using addSelectionListener, you can get notifications, whenever a button is clicked.

package swt_app;

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.SelectionAdapter;
import org.eclipse.swt.events.SelectionEvent;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Text;

public class Test {

  private static int xPosition = 30;
  private static int yPosition = 30;
  private static int width = 500;
  private static int height = 30;
  private static int scrollWidth = 500;
  private static int scrollHeight = 350;

  private static int shellWidth = 600;
  private static int shellHeight = 600;

  private static void addWidgetsToShell(Shell shell) {

    Text text1 = new Text(shell, SWT.BORDER);
    text1.setText("You can't edit me");
    text1.setBounds(xPosition, yPosition, width, height);
    text1.setEditable(false);

    yPosition += 40;

    Text text2 = new Text(shell, SWT.BORDER | SWT.H_SCROLL | SWT.V_SCROLL);
    text2.setText("Bordered scrolled text box");
    text2.setBounds(xPosition, yPosition, scrollWidth, scrollHeight);

    yPosition += 80;

    Button button1 = new Button(shell, SWT.PUSH);
    button1.setText("Submit");
    button1.setLocation(xPosition + 130, yPosition + 300);
    button1.setSize(100, 20);

    Button button2 = new Button(shell, SWT.PUSH);
    button2.setText("Cancel");
    button2.setLocation(xPosition + 260, yPosition + 300);
    button2.setSize(100, 20);

    button1.addSelectionListener(new SelectionAdapter() {
      public void widgetSelected(SelectionEvent e) {
        System.out.println("Submit button was clicked");
      }
    });

    button2.addSelectionListener(new SelectionAdapter() {
      public void widgetSelected(SelectionEvent e) {
        System.out.println("Cancel button was clicked");
      }
    });

  }

  public static void main(String[] args) {

    /* Instantiate Display object, it represents SWT session */
    Display display = new Display();

    /*
     * Define Shell, it represent a window, You can add more than one shell
     * to Display
     */
    Shell shell = new Shell(display);
    shell.setSize(shellWidth, shellHeight);

    addWidgetsToShell(shell);

    /* Open shell window */
    shell.open();

    /*
     * Run the event dispatching loop until an exit condition occurs, which
     * is typically when the main shell window is closed by the user.
     */

    while (!shell.isDisposed()) {
      if (!display.readAndDispatch())
        display.sleep();
    }

    /* Dispose the display */
    display.dispose();
  }
}

Experiment by clicking Submit, Cancel buttons, you can able to see the messages in console.

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