使用消失的文本制作 JTextField

Question

我知道您可以预先将文本输入到 JTextField 中。此文本将显示在 JTextField 中，并且在必须将您自己的文本输入 JTextField 时必须手动删除。例如，考虑这个 JTextField：

cruiseSel = new JTextField ("Selected Cruise:");
cruiseSel.setEditable(false);  
centerP12.add(cruiseSel);
contentPane12.add(centerP12, BorderLayout.CENTER);
Frame12.setVisible(true);

运行上述程序后，将出现一个 JTextField，其中写有“Selected Cruise:”。然后必须手动删除此文本以清除文本字段。

有没有办法在jtextfield中输入文本，因此在GUI打开后，将显示文本，但当jtextfield被选中输入手动文本时，文本会消失？

Answer 1

您可以使用FocusListener，当 JTextField 获得焦点时，清空文本。

当然，您需要一个状态标记来指示它具有默认文本，并且一旦用户输入了文本就不要这样做。在第一次点击 FocusListener 之后或之后，将其移除。

textField.addFocusListener(new FocusAdapter() {
    public void focusGained(FocusEvent e) {
        JTextField source = (JTextField)e.getComponent();
        source.setText("");
        source.removeFocusListener(this);
    }
});

Answer 2

您可以使用SwingX 阅读此How to set Text like Placeholder in JTextfield in swing 我在这里包含示例代码供您使用

import java.awt.EventQueue;
import java.awt.Font;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import org.jdesktop.swingx.prompt.PromptSupport;

public class PromptExample {

    public static void main(String[] args) {
        new PromptExample();
    }

    public PromptExample() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JTextField bunnies = new JTextField(10);
                JTextField ponnies = new JTextField(10);
                JTextField unicorns = new JTextField(10);
                JTextField fairies = new JTextField(10);

                PromptSupport.setPrompt("Bunnies", bunnies);
                PromptSupport.setPrompt("Ponnies", ponnies);
                PromptSupport.setPrompt("Unicorns", unicorns);
                PromptSupport.setPrompt("Fairies", fairies);

                PromptSupport.setFocusBehavior(PromptSupport.FocusBehavior.HIDE_PROMPT, bunnies);
                PromptSupport.setFocusBehavior(PromptSupport.FocusBehavior.HIGHLIGHT_PROMPT, ponnies);
                PromptSupport.setFocusBehavior(PromptSupport.FocusBehavior.SHOW_PROMPT, unicorns);

                PromptSupport.setFontStyle(Font.BOLD, bunnies);
                PromptSupport.setFontStyle(Font.ITALIC, ponnies);
                PromptSupport.setFontStyle(Font.ITALIC | Font.BOLD, unicorns);

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new GridBagLayout());
                GridBagConstraints gbc = new GridBagConstraints();
                gbc.gridwidth = GridBagConstraints.REMAINDER;
                frame.add(bunnies, gbc);
                frame.add(ponnies, gbc);
                frame.add(unicorns, gbc);
                frame.add(fairies, gbc);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

}

Answer 3

查看Text Prompt。

它支持此功能以及一些自定义提示行为的特性。

Answer 4

您要查找的内容称为占位符。我前段时间写过这门课：

import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Insets;
import java.awt.Rectangle;
import java.awt.RenderingHints;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;

/**
 * @author xehpuk
 */
public class PlaceholderTextField extends JTextField {
    private static final long serialVersionUID = -5529071085971698388L;

    /**
     * The placeholder to be displayed if the text field is empty.
     */
    private String placeholder;
    /**
     * Determines whether the placeholder should be displayed even on focus.
     */
    private boolean paintingOnFocus;
    /**
     * The color the placeholder should be displayed in.
     */
    private Color placeholderColor;

    public String getPlaceholder() {
        return placeholder;
    }

    public void setPlaceholder(final String placeholder) {
        this.placeholder = placeholder;
        repaint();
    }

    public boolean isPaintingOnFocus() {
        return paintingOnFocus;
    }

    public void setPaintingOnFocus(final boolean paintingOnFocus) {
        this.paintingOnFocus = paintingOnFocus;
        repaint();
    }

    public Color getPlaceholderColor() {
        return placeholderColor;
    }

    public void setPlaceholderColor(final Color placeholderColor) {
        this.placeholderColor = placeholderColor;
        repaint();
    }

    public PlaceholderTextField() {
        super();
    }

    public PlaceholderTextField(final Document doc, final String text, final int columns) {
        super(doc, text, columns);
    }

    public PlaceholderTextField(final int columns) {
        super(columns);
    }

    public PlaceholderTextField(final String text, final int columns) {
        super(text, columns);
    }

    public PlaceholderTextField(final String text) {
        super(text);
    }

    {
        addFocusListener(new RepaintFocusListener());
    }

    @Override
    protected void paintComponent(final Graphics g) {
        super.paintComponent(g);
        if (getPlaceholder() != null && getText().isEmpty() && (isPaintingOnFocus() || !isFocusOwner())) {
            try {
                final Rectangle rect = getUI().modelToView(this, 0);
                final Insets insets = getInsets();
                g.setFont(getFont());
                g.setColor(getPlaceholderColor() == null ? getForeground() : getPlaceholderColor());
                ((Graphics2D) g).setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
                g.drawString(getPlaceholder(), rect.x, getHeight() - insets.top - insets.bottom - rect.y);
            } catch (final BadLocationException e) {
                throw new RuntimeException(e);
            }
        }
    }

    private class RepaintFocusListener implements FocusListener {
        @Override
        public void focusGained(final FocusEvent e) {
            repaint();
        }

        @Override
        public void focusLost(final FocusEvent e) {
            repaint();
        }
    }
}

您可以选择文本和颜色以及是否应该绘制，即使文本字段有焦点。

关键部分是覆盖paintComponent(Graphics)。

Answer 5

要实现这样的目标，您通常需要创建特定类型的event listener。在您的情况下，需要在鼠标事件上触发所需的操作 - 因此 MouseAdapter 事件侦听器似乎很合适（乍一看）。使用MouseAdapter 抽象类，您需要扩展它并覆盖必要的方法（有关可用方法的完整列表，请参阅here）。

实现这一点的最短方法是通过anonymous class 声明，如下所示：

cruiseSel.addMouseListener(new MouseAdapter(){
    @Override
    public void mouseClicked(MouseEvent e){
        cruiseSel.setText("");
    }
});

（但是，如果您需要覆盖多个方法或触发的逻辑感觉足够复杂，则最好创建一个单独的侦听器类。）

编辑：或者，正如@HovercraftFullOfEels 在评论部分指出的那样，以相同的方式应用FocusAdapter 类（参见here）可能更明智：

cruiseSel.addFocusListener(new FocusAdapter(){
    @Override
    public void focusGained(FocusEvent e){
        cruiseSel.setText("");
    }
});

第一个解决方案的问题在于它只关注文本字段上的实际鼠标点击，而后者则监听任何类型的焦点增益。因此，当使用 TAB 键在文本字段之间切换时，只有第二种解决方案才能正确执行。