Error adding placeholder to a text component

Question

I am implementing the component of this topic together with the following instruction:

PromptSupport.setPrompt("Digite..", field); 

This command is from biblioteca swingx-core-1.6.2 and adds a sort of placeholder. But when using it together with the event FocusListener of a IconTextField he gives me the following mistake:

  Exception in thread "AWT-EventQueue-0" java.lang.StackOverflowError
    at javax.swing.text.DefaultCaret$Handler.propertyChange(DefaultCaret.java:1846)
    at java.beans.PropertyChangeSupport.fire(PropertyChangeSupport.java:335)
    at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:327)
    at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:263)
    at java.awt.Component.firePropertyChange(Component.java:8428)
    at javax.swing.JComponent.setBorder(JComponent.java:1796)
    at geral.IconTextField.setBorder(IconTextField.java:45)
    at org.jdesktop.swingx.plaf.BuddyLayoutAndBorder.replaceBorderIfNecessary(BuddyLayoutAndBorder.java:56)
    at org.jdesktop.swingx.plaf.BuddyLayoutAndBorder.propertyChange(BuddyLayoutAndBorder.java:245)
    at java.beans.PropertyChangeSupport.fire(PropertyChangeSupport.java:335)
    at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:328)
    at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:263)
    at java.awt.Component.firePropertyChange(Component.java:8428)
    at javax.swing.JComponent.setBorder(JComponent.java:1796)
    at geral.IconTextField.setBorder(IconTextField.java:45)
    at org.jdesktop.swingx.plaf.BuddyLayoutAndBorder.replaceBorderIfNecessary(BuddyLayoutAndBorder.java:56)
    at org.jdesktop.swingx.plaf.BuddyLayoutAndBorder.propertyChange(BuddyLayoutAndBorder.java:245)
    at java.beans.PropertyChangeSupport.fire(PropertyChangeSupport.java:335)
    at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:328)
    at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:263)
    at java.awt.Component.firePropertyChange(Component.java:8428)
    at javax.swing.JComponent.setBorder(JComponent.java:1796)
    at geral.IconTextField.setBorder(IconTextField.java:45)

What can I do to solve?

Library link(scroll the page almost at the end, and download the 1st link)

Below I’ll leave the classes I’m using:

Main class:

public class JTextFieldDecoratedIcon {

    public void start() throws IOException {

        final JFrame frame = new JFrame();
        frame.setPreferredSize(new Dimension(500, 350));

        JTextField field2 = new JTextField();
        IconTextField field = new IconTextField();

        URL path = new URL("https://i.imgur.com/WKfl8uV.png");
        Image icone = ImageIO.read(path);

        field.setIcon(new ImageIcon(icone));

        frame.add(field, BorderLayout.NORTH);
        field.setPreferredSize(new Dimension(250, 30));

        //bibilioteca swingx-core-1.6.2 ↓
        PromptSupport.setPrompt("Digite..", field);

        frame.add(field2, BorderLayout.SOUTH);
        field2.setPreferredSize(new Dimension(100, 30));

        field.addFocusListener(new FocusListener() {
            @Override
            public void focusGained(FocusEvent e) {
                field.setBorder(new LineBorder(new Color(108, 85, 255)));
                field.setBackground(Color.LIGHT_GRAY);
            }

            @Override
            public void focusLost(FocusEvent e) {
                field.setBorder(new LineBorder(Color.GRAY));
                field.setBackground(new Color(255, 255, 255));
            }
        });

        frame.pack();
        frame.setVisible(true);
        frame.setLocationRelativeTo(null);

        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {

        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | javax.swing.UnsupportedLookAndFeelException ex) {
            ex.printStackTrace();
        }

        EventQueue.invokeLater(() -> {
            try {
                new JTextFieldDecoratedIcon().start();
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        });
    }
}

Icontextcomponenthelper class :

class IconTextComponentHelper {
    private static final int ICON_SPACING = 4;

    private Border mBorder;
    private Icon mIcon;
    private Border mOrigBorder;
    private JTextComponent mTextComponent;

    IconTextComponentHelper(JTextComponent component) {
        mTextComponent = component;
        mOrigBorder = component.getBorder();
        mBorder = mOrigBorder;
    }

    Border getBorder() {
        return mBorder;
    }

    void onPaintComponent(Graphics g) {
        if (mIcon != null) {
            Insets iconInsets = mOrigBorder.getBorderInsets(mTextComponent);
            mIcon.paintIcon(mTextComponent, g, iconInsets.left, iconInsets.top);
        }
    }

    void onSetBorder(Border border) {
        mOrigBorder = border;

        if (mIcon == null) {
            mBorder = border;
        } else {
            Border margin = BorderFactory.createEmptyBorder(0, mIcon.getIconWidth() + ICON_SPACING, 0, 0);
            mBorder = BorderFactory.createCompoundBorder(border, margin);
        }
    }

    void onSetIcon(Icon icon) {
        mIcon = icon;
        resetBorder();
    }

    private void resetBorder() {
        mTextComponent.setBorder(mOrigBorder);
    }
}

Icontextfield class:

public class IconTextField extends JTextField {

    private IconTextComponentHelper mHelper = new IconTextComponentHelper(this);

    public IconTextField() {

    super();
}

public IconTextField(int cols) {
    super(cols);
}

private IconTextComponentHelper getHelper() {
    if (mHelper == null) {
        mHelper = new IconTextComponentHelper(this);
    }

    return mHelper;
}

@Override
protected void paintComponent(Graphics graphics) {
    super.paintComponent(graphics);
    getHelper().onPaintComponent(graphics);
}

public void setIcon(Icon icon) {
    getHelper().onSetIcon(icon);
}

public void setIconSpacing(int spacing) {
    //getHelper().onSetIconSpacing(spacing);
}

@Override
    public void setBorder(Border border) {
        getHelper().onSetBorder(border);
        super.setBorder(getHelper().getBorder());
    }
}

Answer 1

After testing several times, I realized that the class of this lib uses listeners focus to apply the placeholder, and when you try to override the focus methods, you go into an infinite loop, as your code changes the field and notifies the Listener, that activates the class event to apply the placeholder, and so keep repeating endlessly.

This could be solved if we understood better how the class works PromptSupport until we display the placeholder and change it directly, something that I find more complicated than creating a class of its own with this functionality.

And to implement a placeholder in JTextfield, you need to monitor component focus. Based in this answer and in this other at Soen, I designed the class PlaceHolderSupport as an alternative to this lib:

import java.awt.Color;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Rectangle;

import javax.swing.FocusManager;
import javax.swing.text.JTextComponent;

/**
 * Classe responsável por definir um placeholder a um componente de texto
 * 
 * @author diego
 *
 */
public class PlaceHolderSupport {

    private static JTextComponent textComponent;
    private static String placeHolder = "";

    /**
     * Aplica o texto recebido como placeholder ao componente de texto
     * 
     * @param comp - Componente de texto
     * @param strPlaceHolder - texto do placeholder
     */
    public static void setPlaceHolder(JTextComponent comp, String strPlaceHolder) {

        textComponent = comp;
        placeHolder = strPlaceHolder;
    }

    /**
     * Desenha uma string centralizada no meio do componente representado pelo
     * retangulo
     * 
     * @param g - Instancia de Graphics.
     * @param text - String a ser desenhada.
     * @param rect - Retangulo para centralizar o texto.
     * @param font - Fonte a ser aplicada ao texto
     */
    private static void drawPlaceHolderString(Graphics g, String text, Rectangle rect, Font font) {
        // Obtém as métricas da fonte do texto
        FontMetrics metrics = g.getFontMetrics(font);
        // Determina a coordenada X do texto conforme
        // o tamanho da borda interna esquerda
        int x = textComponent.getBorder().getBorderInsets(textComponent).left;
        // Determina a coordenada Y do texto para que
        // fique centralizado verticalmente
        int y = rect.y + ((rect.height - metrics.getHeight()) / 2) + metrics.getAscent();
        // aplica a fonte
        g.setFont(font);
        // desenha a string
        g.drawString(text, x, y);
    }

    /**
     * Desenha o placeholder no componente de texto
     * 
     * @param g - instancia de Graphics
     */
    public static void onPaintComponent(Graphics g) {

        if (textComponent != null) {
            //verifica se o campo está vazio e se 
            //o foco atual do teclado pertence a ele
            if (textComponent.getText().isEmpty()
                    && !(FocusManager.getCurrentKeyboardFocusManager().getFocusOwner() == textComponent)) {
                Font font = textComponent.getFont().deriveFont(Font.ITALIC);
                g.setColor(Color.gray);
                drawPlaceHolderString(g, placeHolder, textComponent.getBounds(), font);
            } else {
                textComponent.repaint();
            }
        }
    }
}

---

To use, you need to pass the text of placeholder and the instance of the text component in the constructor of this class, using the method setPlaceHolder. In your class example IconTextField, was like this:

public IconTextField() {
    super();
    PlaceHolderSupport.setPlaceHolder(this, "Preencha este campo...");
}

public IconTextField(int cols) {
    super(cols);
    PlaceHolderSupport.setPlaceHolder(this, "Preencha este campo...");
}

Then, in the method paintComponent of your text component, add the following excerpt:

PlaceHolderSupport.onPaintComponent(graphics);

The method PlaceHolderSupport.onPaintComponent checks that the component is empty and out of focus. If the condition is true, it applies the placeholder, and when that condition is not true, it forces the component to redesign without the text.

I also suggest you make a small modification by adding the focus event to the component, as I noticed that you try to recover background colors and pattern edges by losing focus and depending on the Look And Feel applied, may not have the expected result. To always get the default background color, you can change as below:

field.addFocusListener(new FocusListener() {

    Color defaultBg = field.getBackground();

    @Override
    public void focusGained(FocusEvent e) {
        field.setBorder(new LineBorder(new Color(108, 85, 255)));
        field.setBackground(Color.LIGHT_GRAY);
    }

    @Override
    public void focusLost(FocusEvent e) {
        field.setBorder(new LineBorder(Color.GRAY));
        field.setBackground(defaultBg);
    }
});

With these changes, your component is already functional with the placeholder applied: