在从 JTextField 读取之前等待键
Wait for key before reading from a JTextField
我有一个程序可以制作一个带有 JTextField 的 JFrame。如何让它等待文本出现在 JTextField 中/按下回车键?
public static void main(String[] args) {
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
int width = (int) screenSize.getWidth();
int height = (int) screenSize.getHeight();
JFrame frame = new JFrame();
frame.getContentPane().add(new Text());
JTextField field = new JTextField(10);
frame.add(field, BorderLayout.SOUTH);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(width,height-55);
frame.setVisible(true);
// There is a keylistener here called listener. It was 100 lines. Did not want to copy
frame.addKeyListener(listener);
double x = 0;
x = Double.parseDouble(field.getText());
System.out.println(x);
我要
x = Double.parseDouble(field.getText());
到 运行 仅当有人在 JFrame 的 JTextField 中键入内容时。
- 不要使用 KeyListener
- 将 DocumentListener 添加到 JTextField 的文档。
- 在此侦听器内部检查文档是否为空。
- 如果不为空,则更改程序的状态以允许计算,可能通过启用或禁用 JButton 或 Action。
例如:
import java.awt.event.ActionEvent;
import javax.swing.*;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.Document;
public class DisbleButton extends JPanel {
private JTextField field = new JTextField(10);
private ButtonAction buttonAction = new ButtonAction();
private JButton button = new JButton(buttonAction);
public DisbleButton() {
add(field);
add(button);
buttonAction.setEnabled(false);
field.getDocument().addDocumentListener(new FieldDocListener());
}
private class FieldDocListener implements DocumentListener {
@Override
public void changedUpdate(DocumentEvent dEvt) {
testDoc(dEvt);
}
@Override
public void insertUpdate(DocumentEvent dEvt) {
testDoc(dEvt);
}
@Override
public void removeUpdate(DocumentEvent dEvt) {
testDoc(dEvt);
}
private void testDoc(DocumentEvent dEvt) {
Document doc = dEvt.getDocument();
buttonAction.setEnabled(doc.getLength() > 0);
}
}
private class ButtonAction extends AbstractAction {
public ButtonAction() {
super("Press Me");
}
@Override
public void actionPerformed(ActionEvent e) {
// TODO do calculation here!
}
}
private static void createAndShowGui() {
DisbleButton mainPanel = new DisbleButton();
JFrame frame = new JFrame("DisbleButton");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
我有一个程序可以制作一个带有 JTextField 的 JFrame。如何让它等待文本出现在 JTextField 中/按下回车键?
public static void main(String[] args) {
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
int width = (int) screenSize.getWidth();
int height = (int) screenSize.getHeight();
JFrame frame = new JFrame();
frame.getContentPane().add(new Text());
JTextField field = new JTextField(10);
frame.add(field, BorderLayout.SOUTH);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(width,height-55);
frame.setVisible(true);
// There is a keylistener here called listener. It was 100 lines. Did not want to copy
frame.addKeyListener(listener);
double x = 0;
x = Double.parseDouble(field.getText());
System.out.println(x);
我要
x = Double.parseDouble(field.getText());
到 运行 仅当有人在 JFrame 的 JTextField 中键入内容时。
- 不要使用 KeyListener
- 将 DocumentListener 添加到 JTextField 的文档。
- 在此侦听器内部检查文档是否为空。
- 如果不为空,则更改程序的状态以允许计算,可能通过启用或禁用 JButton 或 Action。
例如:
import java.awt.event.ActionEvent;
import javax.swing.*;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.Document;
public class DisbleButton extends JPanel {
private JTextField field = new JTextField(10);
private ButtonAction buttonAction = new ButtonAction();
private JButton button = new JButton(buttonAction);
public DisbleButton() {
add(field);
add(button);
buttonAction.setEnabled(false);
field.getDocument().addDocumentListener(new FieldDocListener());
}
private class FieldDocListener implements DocumentListener {
@Override
public void changedUpdate(DocumentEvent dEvt) {
testDoc(dEvt);
}
@Override
public void insertUpdate(DocumentEvent dEvt) {
testDoc(dEvt);
}
@Override
public void removeUpdate(DocumentEvent dEvt) {
testDoc(dEvt);
}
private void testDoc(DocumentEvent dEvt) {
Document doc = dEvt.getDocument();
buttonAction.setEnabled(doc.getLength() > 0);
}
}
private class ButtonAction extends AbstractAction {
public ButtonAction() {
super("Press Me");
}
@Override
public void actionPerformed(ActionEvent e) {
// TODO do calculation here!
}
}
private static void createAndShowGui() {
DisbleButton mainPanel = new DisbleButton();
JFrame frame = new JFrame("DisbleButton");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}