小编典典

对于它的价值，我发现实际实现它很有趣，因此我想与您分享(我不是在寻求投票)。

这真的是非侵入性的，因为您要做的就是致电new GhostText(textField, "Please enter some text

here...");。剩下的代码只是使它运行。

import java.awt.Color;

import java.awt.Dimension;

import java.awt.event.FocusEvent;

import java.awt.event.FocusListener;

import java.beans.PropertyChangeEvent;

import java.beans.PropertyChangeListener;

import javax.swing.JButton;

import javax.swing.JFrame;

import javax.swing.JPanel;

import javax.swing.JTextField;

import javax.swing.SwingUtilities;

import javax.swing.event.DocumentEvent;

import javax.swing.event.DocumentListener;

public class Test {

public static class GhostText implements FocusListener, DocumentListener, PropertyChangeListener {

private final JTextField textfield;

private boolean isEmpty;

private Color ghostColor;

private Color foregroundColor;

private final String ghostText;

protected GhostText(final JTextField textfield, String ghostText) {

super();

this.textfield = textfield;

this.ghostText = ghostText;

this.ghostColor = Color.LIGHT_GRAY;

textfield.addFocusListener(this);

registerListeners();

updateState();

if (!this.textfield.hasFocus()) {

focusLost(null);

}

}

public void delete() {

unregisterListeners();

textfield.removeFocusListener(this);

}

private void registerListeners() {

textfield.getDocument().addDocumentListener(this);

textfield.addPropertyChangeListener("foreground", this);

}

private void unregisterListeners() {

textfield.getDocument().removeDocumentListener(this);

textfield.removePropertyChangeListener("foreground", this);

}

public Color getGhostColor() {

return ghostColor;

}

public void setGhostColor(Color ghostColor) {

this.ghostColor = ghostColor;

}

private void updateState() {

isEmpty = textfield.getText().length() == 0;

foregroundColor = textfield.getForeground();

}

@Override

public void focusGained(FocusEvent e) {

if (isEmpty) {

unregisterListeners();

try {

textfield.setText("");

textfield.setForeground(foregroundColor);

} finally {

registerListeners();

}

}

}

@Override

public void focusLost(FocusEvent e) {

if (isEmpty) {

unregisterListeners();

try {

textfield.setText(ghostText);

textfield.setForeground(ghostColor);

} finally {

registerListeners();

}

}

}

@Override

public void propertyChange(PropertyChangeEvent evt) {

updateState();

}

@Override

public void changedUpdate(DocumentEvent e) {

updateState();

}

@Override

public void insertUpdate(DocumentEvent e) {

updateState();

}

@Override

public void removeUpdate(DocumentEvent e) {

updateState();

}

}

public static void main(String[] args) {

SwingUtilities.invokeLater(new Runnable() {

@Override

public void run() {

init();

}

});

}

public static void init() {

JFrame frame = new JFrame("Test ghost text");

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

JPanel panel = new JPanel();

JTextField textField = new JTextField();

JButton button = new JButton("Grab focus");

GhostText ghostText = new GhostText(textField, "Please enter some text here...");

textField.setPreferredSize(new Dimension(300, 24));

panel.add(textField);

panel.add(button);

frame.add(panel);

frame.pack();

frame.setVisible(true);

button.grabFocus();

}

}

2020-09-16