java - jTextField 中的 Fantom 文本。如何？

Question

我们遇到一些流行网站的登录屏幕，其中用户名文本框中写有淡灰色的用户名。我想知道这可以在java swings中实现吗？

I have theories, implementing by mouseEvents. Couldn't figure out how to to.

Answer 1

一种方法:

• 创建一个类，在启动时提供 JTextField 虚拟文本
• 将文本的前景设置为浅色
• 使用 FocusListener，它将选择所有虚拟文本并将前景更改为默认颜色(设置为 null)。

例如:

import java.awt.Color;
import java.awt.GridLayout;
import java.awt.event.FocusAdapter;
import java.awt.event.FocusEvent;

import javax.swing.*;

@SuppressWarnings("serial")
public class FantomTextFieldTest extends JPanel {
    FantomTextField fantomTextField = new FantomTextField("Fantom Text");

    public FantomTextFieldTest() {
        setLayout(new GridLayout(1, 0, 5, 0));
        add(new JTextField(20));
        add(fantomTextField.getTextField());
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }

    private static void createAndShowGui() {
        FantomTextFieldTest mainPanel = new FantomTextFieldTest();
        JFrame frame = new JFrame("FantomTextFieldTest");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }
}

class FantomTextField {
    private static final Color FANTOM_FG = new Color(150, 150, 150, 150);
    private JTextField textField;
    private String fantomText;
    private boolean showFantomText = true;

    public FantomTextField(String fantomText) {
        this.fantomText = fantomText;
        textField = new JTextField();
        textField.setText(fantomText);
        textField.setForeground(FANTOM_FG);
        textField.addFocusListener(new FtfFocusListener());
    }

    public FantomTextField(String fantomText, int columns) {
        this(fantomText);
        textField.setColumns(columns);
    }

    public JTextField getTextField() {
        return textField;
    }

    public String getFantomText() {
        return fantomText;
    }

    public void setFantomText(String fantomText) {
        this.fantomText = fantomText;
        textField.setText(fantomText);
        textField.setForeground(FANTOM_FG);
        showFantomText = true;
    }

    private class FtfFocusListener extends FocusAdapter {
        @Override
        public void focusGained(FocusEvent e) {
            if (showFantomText) {
                textField.selectAll();
                textField.setForeground(null);
                showFantomText = false;
            }
        }
    }       
}