Mega Code Archive
Demonstrates various listeners
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//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();
}
}
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