我目前正在制作我们的项目，但在将 JLabel 重置回“0”时遇到问题。这是代码
主要代码片段(请检查注释1以了解所使用的帧处理方法):
import javax.swing.*; //import library
import java.awt.event.*;
import java.awt.*;
import java.util.*;
public class draft_main //class name
{
public static void main(String[] args)
{ //method name
JFrame f0 = new JFrame("POS"); //frame
JPanel p0 = new JPanel(); //panel inside the frame
JPanel p1 = new JPanel();
JPanel p2 = new JPanel();
JPanel p3 = new JPanel();
JPanel p4 = new JPanel();
JPanel p5 = new JPanel();
JPanel p6 = new JPanel();
JPanel p7 = new JPanel();
JLabel l0 = new JLabel("Amount:"); //label inside the panel
JLabel l1 = new JLabel("0");
JLabel l2 = new JLabel("Menu Code: ");
JLabel l3 = new JLabel("--Menu--");
JTextField tf0 = new JTextField("", 12); //user input for menu code
JButton b0 = new JButton("Checkout"); //buttons
JButton b1 = new JButton("Cancel");
JButton b2 = new JButton("Exit");
JButton b4 = new JButton("Accept");
JButton b7 = new JButton("Remove");
JOptionPane jop = new JOptionPane(); //JOptionPane
JTextField tf1 = new JTextField("1. Hot Pockets Pizza", 20); //list of menu
JTextField tf2 = new JTextField("2. Burger with Fries", 20);
JTextField tf3 = new JTextField("3. Sticky Rice (Bico)", 20);
ArrayList<String> ar = new ArrayList<String>(); //list of array
try{
b4.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e) //what the accept button does
{
String order = tf0.getText(), tots="", temp="";
int o = Integer.parseInt(order);
int tot=0;
switch(o) //menu choice
{
case 1 : temp = l1.getText(); tot=Integer.parseInt(temp); tot=tot+250; tots = Integer.toString(tot); l1.setText(tots); ar.add("Hot Pockets Pizza"); break;
case 2 : temp = l1.getText(); tot=Integer.parseInt(temp); tot=tot+65; tots = Integer.toString(tot); l1.setText(tots); ar.add("Burger with Fries"); break;
case 3 : temp = l1.getText(); tot=Integer.parseInt(temp); tot=tot+12; tots = Integer.toString(tot); l1.setText(tots); ar.add("Sticky Rice (Bico)"); break;
default : jop.showMessageDialog(null, "Menu code not listed in menu", "Error", jop.INFORMATION_MESSAGE); break;
}
}
});
b0.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e) //what the checkout button does
{
JFrame f1 = new JFrame("Checkout");
JFrame f2 = new JFrame("Order");
JPanel p8 = new JPanel();
JPanel p9 = new JPanel();
JPanel p10 = new JPanel();
JPanel p11 = new JPanel();
JPanel p12 = new JPanel();
JPanel p13 = new JPanel();
JPanel p14 = new JPanel();
JLabel l5 = new JLabel("Order list");
JLabel l6 = new JLabel(/*convert ArrayList to String then put here*/);
JLabel l4 = new JLabel("Cash");
JTextField tf4 = new JTextField("", 14);
JButton b5 = new JButton("Accept");
JButton b6 = new JButton("Cancel");
JButton b7 = new JButton("Ok");
b5.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
String cas = l1.getText(), in = tf4.getText();
int cash = Integer.parseInt(cas), inp = Integer.parseInt(in), cahs=0;
if(cash>inp)
{
jop.showMessageDialog(null, "Insufficient funds", "Lacking cash? Work for it.", jop.INFORMATION_MESSAGE);
}
else if(cash<inp)
{
cahs = inp - cash;
jop.showMessageDialog(null, "Change: " +cahs+". Thank you");
f1.dispatchEvent(new WindowEvent(f1, WindowEvent.WINDOW_CLOSING));
}
else if(cash==inp)
{
jop.showMessageDialog(null, "Thank you.", "Thank you.", jop.INFORMATION_MESSAGE);
f1.dispatchEvent(new WindowEvent(f1, WindowEvent.WINDOW_CLOSING));
}
}
});
b6.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
f1.dispatchEvent(new WindowEvent(f1, WindowEvent.WINDOW_CLOSING));
}
});
b7.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
f2.dispatchEvent(new WindowEvent(f2, WindowEvent.WINDOW_CLOSING));
}
});
p9.add(l0);
p9.add(l1);
p10.add(l4);
p10.add(tf4);
p11.add(b5);
p11.add(b6);
p12.add(l5);
p12.add(l6);
p13.add(b7);
p14.add(p12);
p14.add(p13);
p8.add(p10);
p8.add(p11);
p8.add(p9);
f1.add(p8);
f1.pack();
f1.setSize(240,170);
f1.setLocationRelativeTo(null);
f1.setResizable(false);
f1.setDefaultCloseOperation(f1.DISPOSE_ON_CLOSE);
f1.setVisible(true);
f2.add(p14);
f2.pack();
f2.setSize(270,100);
f2.setResizable(false);
f2.setLocationRelativeTo(null);
f2.setDefaultCloseOperation(f2.DISPOSE_ON_CLOSE);
f2.setVisible(true);
}
});
b1.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
l1.setText("0");
}
});
b2.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
f0.dispose();
}
});
}
catch(Exception e)
{
jop.showMessageDialog(null, "Error");
}
tf1.setEditable(false);
tf2.setEditable(false);
tf3.setEditable(false);
p4.add(tf1);
p5.add(tf2);
p6.add(tf3);
p7.add(l3);
p3.add(l2);
p3.add(tf0);
p3.add(b4);
p1.add(l0);
p1.add(l1);
p2.add(b0);
p2.add(b1);
p2.add(b2);
p0.add(p3);
p0.add(p1);
p0.add(p2);
p0.add(p7);
p0.add(p4);
p0.add(p5);
p0.add(p6);
f0.add(p0);
f0.pack();
f0.setSize(303,280);
f0.setLocationRelativeTo(null);
f0.setResizable(false);
f0.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f0.setVisible(true);
}
}
当主窗口打开时，它会询问一个人从菜单中订购了哪个，然后显示价格。结帐时，用户将被要求输入所给的现金金额，并在有零钱时找零。之后，结账框架被“正确”处理(我认为是这样)，暴露了主框架。然而，当我下另一个订单或清除当前订单时，JLabel 似乎没有更新，这让我很困扰，因为主框架应该是完全交互的，直到主框架关闭。
注意#1:我使用了不同的方法来处理弹出的第二个和第三个框架，因为我认为这可能是因为 dispose();并没有真正破坏框架，而是让它在后台运行。
注意#2:是的，该程序尚未完成，但目前这些并不重要，因为这些只是应用程序的一些小功能。
最佳答案
这段代码存在几个问题，但我看到的主要问题(我还没有完成所有问题，所以可能还有更多)
- 首先，这些 JFrame 子窗口根本不应该是 JFrame，而应该是模态 JDialog。这样做的原因是，当使用这些对话框时，您可以完全控制程序流程，因为您将知道当模式对话框可见时主程序流程将被搁置，然后流程将立即恢复因为对话框不再可见。这样您就可以在处理完对话框后查询其状态，然后使用此信息来更新您的 GUI。
- 您的金额显示在
l1变量中，除非您专门对此变量调用setText(...)，否则该金额永远不会改变。订单处理完毕后，您似乎并未执行此操作。模式对话框将再次帮助您。 - 你的变量命名不好。不要使用无意义的字母和数字作为名称，而应使用有意义的名称，并使您的代码具有 self 注释功能。例如，使用
amountLabel或类似的东西来代替l1。 您的代码是一个巨大的上帝类，所有内容都塞进了静态 main 方法中，这造成了调试噩梦。 Java 是一种面向对象的语言，如果使用得当，OOP 技术可以帮助您降低程序复杂性，使您的代码更容易为您自己和我们所理解。开始对您的程序进行 OOP 化，您将立即看到红利。
我发现了您的错误 - 您将
l1JLabel 添加到另一个容器，因此它实际上已从原始 JFrame 中删除。如果您最小化原始 GUI 然后恢复它，您将看到 l1 JLabel 的数量消失。
这里有一些尚未完成的示例代码，但可以让您了解如何将 OOP 添加到程序中:
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.text.NumberFormat;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;
@SuppressWarnings("serial")
public class Draft2 extends JPanel {
private List<MyItem> selectedItems = new ArrayList<>();
private NumberFormat formatter = NumberFormat.getCurrencyInstance();
private double total;
private JLabel totalAmountLabel = new JLabel(formatter.format(total));
private DefaultComboBoxModel<MyItem> comboModel = new DefaultComboBoxModel<>();
private JComboBox<MyItem> menuCombo = new JComboBox<>(comboModel);
public Draft2() {
// monospaced to make names and price line up
menuCombo.setFont(new Font(Font.MONOSPACED, Font.BOLD, 12));
// fill the JComboBox with items
comboModel.addElement(new MyItem("Baseball", 21.5));
comboModel.addElement(new MyItem("Bat", 50.8));
comboModel.addElement(new MyItem("Football", 22.26));
// create a JPanel to hold selection components and add components
JPanel selectionPanel = new JPanel();
selectionPanel.add(new JLabel("Menu:"));
selectionPanel.add(menuCombo);
selectionPanel.add(new JButton(new AcceptAction("Accept", KeyEvent.VK_A)));
// create a JPanel to hold the total amount information
JPanel totalAmountPanel = new JPanel();
totalAmountPanel.add(new JLabel("Total Amount:"));
totalAmountPanel.add(totalAmountLabel);
// create a JPanel to hold buttons, uses grid layout with a single row
JPanel btnPanel = new JPanel(new GridLayout(1, 0, 5, 0));
btnPanel.add(new JButton(new CheckOutAction("Check Out", KeyEvent.VK_C)));
btnPanel.add(new JButton(new CancelAction("Cancel", KeyEvent.VK_N)));
btnPanel.add(new JButton(new ExitAction("Exit", KeyEvent.VK_X)));
setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));
add(selectionPanel);
add(Box.createVerticalStrut(5)); // so don't crowd things
add(totalAmountPanel);
add(Box.createVerticalStrut(5));
add(btnPanel);
}
public void setTotalAmount(double total) {
totalAmountLabel.setText(formatter.format(total));
}
private class AcceptAction extends AbstractAction {
public AcceptAction(String name, int mnemonic) {
super(name);
putValue(MNEMONIC_KEY, mnemonic);
}
@Override
public void actionPerformed(ActionEvent e) {
MyItem myMenuItem = (MyItem) menuCombo.getSelectedItem();
if (myMenuItem == null) {
return; // nothing selected, get out
}
selectedItems.add(myMenuItem);
double total = 0.0;
for (MyItem myItem : selectedItems) {
total += myItem.getCost();
}
setTotalAmount(total);
}
}
private class CheckOutAction extends AbstractAction {
public CheckOutAction(String name, int mnemonic) {
super(name);
putValue(MNEMONIC_KEY, mnemonic);
}
@Override
public void actionPerformed(ActionEvent e) {
// TODO Finish....
// open JDialog or JOptionPane
}
}
private class CancelAction extends AbstractAction {
public CancelAction(String name, int mnemonic) {
super(name);
putValue(MNEMONIC_KEY, mnemonic);
}
@Override
public void actionPerformed(ActionEvent e) {
// TODO Finish...
}
}
private class ExitAction extends AbstractAction {
public ExitAction(String name, int mnemonic) {
super(name);
putValue(MNEMONIC_KEY, mnemonic);
}
@Override
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
}
}
private static void createAndShowGui() {
JFrame frame = new JFrame("My GUI Example");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new Draft2());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> {
createAndShowGui();
});
}
}
class MyItem {
private NumberFormat formatter = NumberFormat.getCurrencyInstance();
private String name;
private double cost;
public MyItem(String name, double cost) {
this.name = name;
this.cost = cost;
}
public String getName() {
return name;
}
public double getCost() {
return cost;
}
@Override
public String toString() {
return String.format("%-10s %s", name, formatter.format(cost));
}
}
关于Java - 正确处理不同的 JFrame 后 JLabel 损坏，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/35799546/