带有输入提示的 Java JTextField

input java hint swing jtextfield

2022-08-31 22:20:14

我想在我的javax.swing.JTextField中添加一个提示值。它应该看起来像火狐渲染 .这将创建一个编辑字段，背景中带有文本“bla”。如果文本框具有焦点，则标题文本将消失，并且当用户离开没有文本的编辑框时，标题文本将重新出现。<input type="text" title="bla">

是否有（自由）摆动组件可以执行此类操作？

答案 1

您可以创建自己的：

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import javax.swing.*;

public class Main {

  public static void main(String[] args) {

    final JFrame frame = new JFrame();

    frame.setLayout(new BorderLayout());

    final JTextField textFieldA = new HintTextField("A hint here");
    final JTextField textFieldB = new HintTextField("Another hint here");

    frame.add(textFieldA, BorderLayout.NORTH);
    frame.add(textFieldB, BorderLayout.CENTER);
    JButton btnGetText = new JButton("Get text");

    btnGetText.addActionListener(new ActionListener() {
      @Override
      public void actionPerformed(ActionEvent e) {
        String message = String.format("textFieldA='%s', textFieldB='%s'",
            textFieldA.getText(), textFieldB.getText());
        JOptionPane.showMessageDialog(frame, message);
      }
    });

    frame.add(btnGetText, BorderLayout.SOUTH);
    frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    frame.setVisible(true);
    frame.pack();
  }
}

class HintTextField extends JTextField implements FocusListener {

  private final String hint;
  private boolean showingHint;

  public HintTextField(final String hint) {
    super(hint);
    this.hint = hint;
    this.showingHint = true;
    super.addFocusListener(this);
  }

  @Override
  public void focusGained(FocusEvent e) {
    if(this.getText().isEmpty()) {
      super.setText("");
      showingHint = false;
    }
  }
  @Override
  public void focusLost(FocusEvent e) {
    if(this.getText().isEmpty()) {
      super.setText(hint);
      showingHint = true;
    }
  }

  @Override
  public String getText() {
    return showingHint ? "" : super.getText();
  }
}

如果您仍在使用 Java 1.5，请将 .this.getText().isEmpty()this.getText().length() == 0

答案 2

这里有一个简单的方法，在任何L&F中看起来都很好：

public class HintTextField extends JTextField {
    public HintTextField(String hint) {
        _hint = hint;
    }
    @Override
    public void paint(Graphics g) {
        super.paint(g);
        if (getText().length() == 0) {
            int h = getHeight();
            ((Graphics2D)g).setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING,RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
            Insets ins = getInsets();
            FontMetrics fm = g.getFontMetrics();
            int c0 = getBackground().getRGB();
            int c1 = getForeground().getRGB();
            int m = 0xfefefefe;
            int c2 = ((c0 & m) >>> 1) + ((c1 & m) >>> 1);
            g.setColor(new Color(c2, true));
            g.drawString(_hint, ins.left, h / 2 + fm.getAscent() / 2 - 2);
        }
    }
    private final String _hint;
}