MultipleListenersExample.java Source code

Introduction

Here is the source code for MultipleListenersExample.java

Source

//Send questions, comments, bug reports, etc. to the authors:

//Rob Warner (rwarner@interspatial.com)
//Robert Harris (rbrt_harris@yahoo.com)

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.*;
import org.eclipse.swt.layout.*;
import org.eclipse.swt.widgets.*;

/**
 * This class demonstrates various listeners
 */
public class MultipleListenersExample implements HelpListener, VerifyListener, ModifyListener {

    // Constants used for conversions
    private static final double FIVE_NINTHS = 5.0 / 9.0;
    private static final double NINE_FIFTHS = 9.0 / 5.0;

    // Widgets used in the window
    private Text fahrenheit;
    private Text celsius;
    private Label help;

    /**
     * Runs the application
     */
    public void run() {
        Display display = new Display();
        Shell shell = new Shell(display);
        shell.setText("Temperatures");
        createContents(shell);
        shell.pack();
        shell.open();
        while (!shell.isDisposed()) {
            if (!display.readAndDispatch()) {
                display.sleep();
            }
        }
        display.dispose();
    }

    /**
     * Create the main window's contents
     * @param shell the main window
     */
    private void createContents(Shell shell) {
        shell.setLayout(new GridLayout(3, true));

        // Create the label and input box for Fahrenheit
        new Label(shell, SWT.LEFT).setText("Fahrenheit:");
        fahrenheit = new Text(shell, SWT.BORDER);
        GridData data = new GridData(GridData.FILL_HORIZONTAL);
        data.horizontalSpan = 2;
        fahrenheit.setLayoutData(data);

        // Set the context-sensitive help
        fahrenheit.setData("Type a temperature in Fahrenheit");

        // Add the listeners
        fahrenheit.addHelpListener(this);
        fahrenheit.addVerifyListener(this);
        fahrenheit.addModifyListener(this);

        // Create the label and input box for Celsius
        new Label(shell, SWT.LEFT).setText("Celsius:");
        celsius = new Text(shell, SWT.BORDER);
        data = new GridData(GridData.FILL_HORIZONTAL);
        data.horizontalSpan = 2;
        celsius.setLayoutData(data);

        // Set the context-sensitive help
        celsius.setData("Type a temperature in Celsius");

        // Add the listeners
        celsius.addHelpListener(this);
        celsius.addVerifyListener(this);
        celsius.addModifyListener(this);

        // Create the area for help
        help = new Label(shell, SWT.LEFT | SWT.BORDER);
        data = new GridData(GridData.FILL_HORIZONTAL);
        data.horizontalSpan = 3;
        help.setLayoutData(data);
    }

    /**
     * Called when user requests help
     */
    public void helpRequested(HelpEvent event) {
        // Get the help text from the widget and set it into the help label
        help.setText((String) event.widget.getData());
    }

    /**
     * Called when the user types into a text box, but before the text box gets
     * what the user typed
     */
    public void verifyText(VerifyEvent event) {
        // Assume we don't allow it
        event.doit = false;

        // Get the character typed
        char myChar = event.character;
        String text = ((Text) event.widget).getText();

        // Allow '-' if first character
        if (myChar == '-' && text.length() == 0)
            event.doit = true;

        // Allow 0-9
        if (Character.isDigit(myChar))
            event.doit = true;

        // Allow backspace
        if (myChar == '\b')
            event.doit = true;
    }

    /**
     * Called when the user modifies the text in a text box
     */
    public void modifyText(ModifyEvent event) {
        // Remove all the listeners, so we don't enter any infinite loops
        celsius.removeVerifyListener(this);
        celsius.removeModifyListener(this);
        fahrenheit.removeVerifyListener(this);
        fahrenheit.removeModifyListener(this);

        // Get the widget whose text was modified
        Text text = (Text) event.widget;

        try {
            // Get the modified text
            int temp = Integer.parseInt(text.getText());

            // If they modified fahrenheit, convert to Celsius
            if (text == fahrenheit) {
                celsius.setText(String.valueOf((int) (FIVE_NINTHS * (temp - 32))));
            } else {
                // Convert to fahrenheit
                fahrenheit.setText(String.valueOf((int) (NINE_FIFTHS * temp + 32)));
            }
        } catch (NumberFormatException e) {
            /* Ignore */ }

        // Add the listeners back
        celsius.addVerifyListener(this);
        celsius.addModifyListener(this);
        fahrenheit.addVerifyListener(this);
        fahrenheit.addModifyListener(this);
    }

    /**
     * The application entry point
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        new MultipleListenersExample().run();
    }
}