* * This program demonstrates navigation features, input validation, and * focus changes. * After entering a value in a text field, there are three ways for the * user to advance to another field: (i) pressing ENTER on the keyboard, * (ii) pressing TAB on the keyboard, or (iii) clicking in a different * text field with the mouse pointer. All three are implemented in * this demo, along with the unsavory act of input validation.
*
* Input validation is performed at the focus level, as presented
* and discussed in DemoInputValidation2.
*
* * If an entry is deemed invalid, an error message is presented in a * popup message dialog. Upon acknowledging the message, focus returns * to the text field containing the invalid entry. The entry must * be corrected before focus can change to another text field.
* * Performing input validation in text fields in concert with managing * focus changes is a bit messy if the GUI also includes popup dialogs * or menus, because traversing menu items and opening and * closing popup dialogs * also trigger focus events. * The approach taken here is explained below. *
*
* A logical time to validate input
* is when the user finishes entering a value. This act is signaled
* when the user presses ENTER, presses TAB, or clicks in another field, as noted
* above. All three of these actions trigger a focus lost event.
* So, input validation is performed in the
* focusLost method of the FocusListener.
* If the content is deemed invalid, then one possible interaction is
* to present a popup dialog informing the user of the problem. The user
* acknowledges the error, clicks OK to close the popup window, then
* corrects the error. However, closing the popup window also
* triggers a focus lost event. There is the potential for an infinite
* loop of focus lost events. This is averted by including the following
* in the focusLost method (Note: fe is the
* FocusEvent argument passed focusLost):
* *
* if (fe.isTemporary()) * return; ** * This prevents the invalid data from being immediately re-validated * when the user closes the popup dialog (which would immediately cause * the popup dialog to reappear, and so on). For a simple demonstration * of this, just comment-out the two lines above, re-compile, and execute. *
*
* Screen snap...
*
* * @see source code * @author Scott MacKenzie, 2002 */ public class DemoTextField { public static void main(String[] args) { // use look and feel for my system (Win32) try { UIManager.setLookAndFeel( UIManager.getSystemLookAndFeelClassName()); } catch (Exception e) {} DemoTextFieldFrame frame = new DemoTextFieldFrame(); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setTitle("DemoTextField"); frame.pack(); frame.show(); } } class DemoTextFieldFrame extends JFrame implements ActionListener, FocusListener { private JTextField messageInput; private JTextField messageDisplay; private JTextField redForeground; private JTextField greenForeground; private JTextField blueForeground; private JTextField redBackground; private JTextField greenBackground; private JTextField blueBackground; String message; int redF, greenF, blueF; int redB, greenB, blueB; public DemoTextFieldFrame() { message = "(enter message above)"; // initial message redF = greenF = blueF = 0; // black foreground redB = greenB = blueB = 255; // white background // ---------------------------------- // construct and configure components // ---------------------------------- final int MESSAGE_SIZE = 20; messageInput = new JTextField(MESSAGE_SIZE); messageInput.setEditable(true); messageDisplay = new JTextField(MESSAGE_SIZE); messageDisplay.setPreferredSize(new Dimension(1, 100)); messageDisplay.setFont(new Font("serif", Font.PLAIN, 24)); messageDisplay.setEditable(false); messageDisplay.setHorizontalAlignment(SwingConstants.CENTER); // set default message and foreground/background colors messageDisplay.setText(message); messageDisplay.setForeground(new Color(redF, greenF, blueF)); messageDisplay.setBackground(new Color(redB, greenB, blueB)); final int SIZE = 8; redForeground = new JTextField("" + redF, SIZE); greenForeground = new JTextField("" + greenF, SIZE); blueForeground = new JTextField("" + blueF, SIZE); redBackground = new JTextField("" + redB, SIZE); greenBackground = new JTextField("" + greenB, SIZE); blueBackground = new JTextField("" + blueB, SIZE); // need a bit of space on the left messageInput.setMargin(new Insets(0, 3, 0, 0)); redForeground.setMargin(new Insets(0, 3, 0, 0)); greenForeground.setMargin(new Insets(0, 3, 0, 0)); blueForeground.setMargin(new Insets(0, 3, 0, 0)); redBackground.setMargin(new Insets(0, 3, 0, 0)); greenBackground.setMargin(new Insets(0, 3, 0, 0)); blueBackground.setMargin(new Insets(0, 3, 0, 0)); redBackground.setMargin(new Insets(0, 3, 0, 0)); // ------------- // add listeners // ------------- messageInput.addActionListener(this); redForeground.addActionListener(this); greenForeground.addActionListener(this); blueForeground.addActionListener(this); redBackground.addActionListener(this); greenBackground.addActionListener(this); blueBackground.addActionListener(this); messageInput.addFocusListener(this); redForeground.addFocusListener(this); greenForeground.addFocusListener(this); blueForeground.addFocusListener(this); redBackground.addFocusListener(this); greenBackground.addFocusListener(this); blueBackground.addFocusListener(this); // ----------------- // layout components // ----------------- // add components to panels JPanel messageInputPanel = new JPanel(); messageInputPanel.add(messageInput); messageInputPanel.setBorder(new TitledBorder(new EtchedBorder(), "Please enter a message")); JPanel f1 = new JPanel(); f1.setLayout(new GridLayout(0, 1)); f1.add(new JLabel("Red ", SwingConstants.RIGHT)); f1.add(new JLabel("Green ", SwingConstants.RIGHT)); f1.add(new JLabel("Blue ", SwingConstants.RIGHT)); JPanel f2 = new JPanel(); f2.setLayout(new GridLayout(0, 1)); f2.add(redForeground); f2.add(greenForeground); f2.add(blueForeground); JPanel foregroundPanel = new JPanel(); foregroundPanel.setLayout(new BorderLayout()); foregroundPanel.add(f1, "West"); foregroundPanel.add(f2, "East"); foregroundPanel.setBorder(new TitledBorder(new EtchedBorder(), "Foreground colour")); JPanel b1 = new JPanel(); b1.setLayout(new GridLayout(0, 1)); b1.add(new JLabel("Red ", SwingConstants.RIGHT)); b1.add(new JLabel("Green ", SwingConstants.RIGHT)); b1.add(new JLabel("Blue ", SwingConstants.RIGHT)); JPanel b2 = new JPanel(); b2.setLayout(new GridLayout(0, 1)); b2.add(redBackground); b2.add(greenBackground); b2.add(blueBackground); JPanel backgroundPanel = new JPanel(); backgroundPanel.setLayout(new BorderLayout()); backgroundPanel.add(b1, "West"); backgroundPanel.add(b2, "East"); backgroundPanel.setBorder(new TitledBorder(new EtchedBorder(), "Background colour")); JPanel colourPanel = new JPanel(); colourPanel.add(foregroundPanel); colourPanel.add(backgroundPanel); // arrange panels JPanel top = new JPanel(); top.setLayout(new BoxLayout(top, BoxLayout.Y_AXIS)); top.add(messageInputPanel); top.add(colourPanel); JPanel contentPane = new JPanel(); contentPane.setLayout(new BorderLayout()); contentPane.add(top, "Center"); contentPane.add(messageDisplay, "South"); // make panel this JFrame's content pane this.setContentPane(contentPane); } // -------------------------------- // implement ActionListener methods // -------------------------------- public void actionPerformed(ActionEvent ae) { JTextField source = (JTextField)ae.getSource(); source.transferFocus(); // Note: triggers focus lost event } // ------------------------------- // implement FocusListener methods // ------------------------------- public void focusGained(FocusEvent fe) {} public void focusLost(FocusEvent fe) { // The Error dialog, when invoked, causes a temporary lost of focus. // Exit now (otherwise an infinite loop results). if (fe.isTemporary()) return; // if reached here, source must be a JTextField JTextField source = (JTextField)fe.getSource(); if (source == messageInput) update(); else if (validate(source)) update(); } // ------------- // Other methods // ------------- /** Update the message according to the values in the various fields. * * @return int - 0 if the update was successful, -1 otherwise */ public void update() { // get message message = messageInput.getText(); // get RGB values (F = foreground, B = background) redF = Integer.parseInt(redForeground.getText()); greenF = Integer.parseInt(greenForeground.getText()); blueF = Integer.parseInt(blueForeground.getText()); redB = Integer.parseInt(redBackground.getText()); greenB = Integer.parseInt(greenBackground.getText()); blueB = Integer.parseInt(blueBackground.getText()); // update the message and foreground/background colors messageDisplay.setText(message); messageDisplay.setForeground(new Color(redF, greenF, blueF)); messageDisplay.setBackground(new Color(redB, greenB, blueB)); } /** Validate an RGB value in a JTextField. * * @param source the JTextField containing the text to validate (must * be an integer in the range 0-255) * @return a boolean: true if validation successful, false otherwise */ public boolean validate(JTextField source) { final boolean SUCCESS = true; final boolean ERROR = false; // validate input int n = getNewValue(source.getText()); if (n == -1) { Toolkit.getDefaultToolkit().beep(); JOptionPane.showMessageDialog(this, "Value must be an integer in the range 0-255", "Invalid Input", JOptionPane.ERROR_MESSAGE ); source.requestFocus(); return ERROR; } return SUCCESS; } /** Input validation: The dirty work of converting a string to * an integer color value in the range 0-255. * * @param newColor a string representing a color value (must be * in the range 0-255) * @return int - the integer color value or -1 if invalid input */ public int getNewValue(String newColor) { int clr; try { clr = Integer.parseInt(newColor); } catch (NumberFormatException e) { return -1; } if (clr < 0 || clr > 255) return -1; return clr; } }