Question

每当我按下退格键或从当前位置删除时，我都需要通过jtextfield擦除jlabel中的数据。我想出了如何在jlable（数值数据）中添加数据，但不知道如何擦除或编辑它。

//这是我的代码

            String  str = "";

       private void jTextField1KeyPressed (java.awt.event.KeyEvent evt) {                                       

           char ch=evt.getKeyChar();

            if(Character.isDigit(ch)
               str += ch; 

            jLabel2.setText(str);
        }



}

Answer 1

使用DocumentListener代替KeyListener，它可以检测用户何时将文字粘贴到字段中和/或以编程方式更改
更新Document后，从字段中获取文本并设置标签文本。当信息已在字段/ String中可用时，尝试更新另一个Document几乎没有任何好处。如果你“真的”必须使用StringBuilder代替它，它会更有效并且是可变的

例如

import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;

public class Test {

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

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

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private JLabel mirrorLabel;

        public TestPane() {
            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridwidth = GridBagConstraints.REMAINDER;

            JTextField field = new JTextField(10);
            field.getDocument().addDocumentListener(new DocumentListener() {

                @Override
                public void insertUpdate(DocumentEvent e) {
                    updateLabel(e.getDocument());
                }

                @Override
                public void removeUpdate(DocumentEvent e) {
                    updateLabel(e.getDocument());
                }

                @Override
                public void changedUpdate(DocumentEvent e) {
                    updateLabel(e.getDocument());
                }

                protected void updateLabel(Document document) {
                    try {
                        mirrorLabel.setText(document.getText(0, document.getLength()));
                    } catch (BadLocationException ex) {
                        ex.printStackTrace();
                    }
                }
            });
            add(field, gbc);

            mirrorLabel = new JLabel(" ");
            add(mirrorLabel, gbc);
        }

    }

}

在keyPressed事件上的jlablel中显示jtextfield数据

1 个答案: