如果您查看下面的代码，我试图做的是修改我的addExpense（）方法以生成一个新的ExpensePanel并将其添加到我的一个面板（面板3）和向量中并更新UI小组3并更新统计数据。
然而，经过无数次的修改，我似乎无法让它发挥作用。任何人都可以提供一些见解吗？
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import java.awt.Panel;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Vector;
import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextField;
import javax.swing.UIManager;
class Expenses extends JFrame implements ActionListener{
ExpensesPanel widget;
public String n;
public String d;
public int c;
public int e;
public Expenses(){
// Set Dimension, size, and close operations
setSize(400,400);
setTitle("Expenses");
setDefaultCloseOperation(EXIT_ON_CLOSE);
setResizable(true);
setLocationRelativeTo(null);
// Set the look and feel of the application to that if the OS
try{
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch(Exception e){
System.out.print(e);
}
// Add Panel 1, or our main panel
JPanel p1 = new JPanel();
getContentPane().add(p1);
p1.setLayout(new BoxLayout(p1, BoxLayout.Y_AXIS));
// Add our second panel, panel 2 with a grid layout
JPanel p2 = new JPanel();
p2.setLayout(new GridLayout(4,2));
p1.add(p2);
// Add our labels
JLabel label1 = new JLabel("Name: ", JLabel.LEFT);
JTextField name = new JTextField(JTextField.EAST);
n = name.getText();
JLabel label2 = new JLabel("Date: ", JLabel.LEFT);
JTextField date = new JTextField(JTextField.EAST);
d = date.getText();
JLabel label3 = new JLabel("Cost: ", JLabel.LEFT);
JTextField cost = new JTextField(JTextField.EAST);
p2.add(label1);
p2.add(name);
p2.add(label2);
p2.add(date);
p2.add(label3);
p2.add(cost);
// Add our buttons
JButton b1 = new JButton("Add");
p2.add(b1);
JButton b2 = new JButton("Clear");
p2.add(b2);
// Set the preferred size of our windows
p2.setMaximumSize(new Dimension(Integer.MAX_VALUE, p2.getPreferredSize().height));
// Panel 3, this will hold the expenses panel
final JPanel p3 = new JPanel();
p3.setLayout(new BoxLayout(p3, BoxLayout.Y_AXIS));
JScrollPane scroll = new JScrollPane(p3);
p1.add(scroll);
// Panel 4, with a 2x2 Grid
JPanel p4 = new JPanel();
p4.setLayout(new GridLayout(2,2));
p1.add(p4);
// Add labels, and ensure they are not editable
JLabel p4l1 = new JLabel("Total", JLabel.LEFT);
JTextField p4t1 = new JTextField(JTextField.EAST);
p4t1.setEditable(false);
JLabel p4l2 = new JLabel("Average", JLabel.LEFT);
JTextField p4t2 = new JTextField(JTextField.EAST);
p4t2.setEditable(false);
p4.add(p4l1);
p4.add(p4t1);
p4.add(p4l2);
p4.add(p4t2);
// Set the preferred size to fit the rest of the window
p4.setMaximumSize(new Dimension(Integer.MAX_VALUE, p2.getPreferredSize().height));
// Action listeners for both buttons
// Action listner for button 1
b1.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e) {
System.out.println("Button 1 Clicked");
addExpense(p3);
}
});
// Action Listener for button 2
b2.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e) {
System.out.println("Button 2 Clicked");
}
});
}
public void addExpense(JPanel p3){
Vector expenseHolder = new Vector();
ExpensesPanel e = new ExpensesPanel(n, d, 2, 1);
p3.add(e);
expenseHolder.add(p3);
p3.revalidate();
}
@Override
public void actionPerformed(ActionEvent arg0) {
// TODO Auto-generated method stub
}
public static void main(String[] args){
// Main method
Expenses e = new Expenses();
// Set the application to be visible
e.setVisible(true);
}
}
class ExpensesPanel extends JPanel{
public String n;
public String d;
public int c;
public int e;
public ExpensesPanel(String name, String date, int cost, int expense){
n = name; d = date; c = cost; e = expense;
// Create new Panel and set it on horizontal axis
JPanel exp = new JPanel();
exp.setLayout(new BoxLayout(exp, BoxLayout.X_AXIS));
Box horizontalBox;
// Labels
JLabel newName = new JLabel("Name: ", JLabel.CENTER);
JLabel newDate = new JLabel("Date", JLabel.CENTER);
JLabel newCost = new JLabel("Cost: ", JLabel.CENTER);
JLabel newExp = new JLabel("Expense: ", JLabel.CENTER);
exp.add(newName, Box.createHorizontalGlue());
exp.add(newDate, Box.createHorizontalGlue());
exp.add(newCost, Box.createHorizontalGlue());
exp.add(newExp, Box.createHorizontalGlue());
}
// Override default paint component
public void paintComponent(Graphics g){
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setBackground(Color.BLUE);
}
}
答案 0 :(得分：1)
你的问题是你的ExpensePanel类有两个 JPanels，一个是你要调用的组件，exp，另一个是this或JPanel，它是该类的对象，你没有添加任何组件。那么你将第二个JPanel添加到GUI中，这样就不会显示任何内容。另请注意，exp在构造函数中声明，因此其范围仅限于构造函数。
一种可能的解决方案：摆脱 exp 并将所有内容添加到this。请注意，您可以使用this.表达式，例如this.add(someComponent)明确表明您的意图，但这是不必要的，并添加额外的单词，在这种情况下几乎没有任何好处，所以我通常避免它
即，将构造函数更改为：
public ExpensesPanel(String name, String date, int cost, int expense) {
n = name;
d = date;
c = cost;
e = expense;
// Create new Panel and set it on horizontal axis
// JPanel exp = new JPanel();
setLayout(new BoxLayout(this, BoxLayout.X_AXIS));
Box horizontalBox;
// Labels
JLabel newName = new JLabel("Name: ", JLabel.CENTER);
JLabel newDate = new JLabel("Date", JLabel.CENTER);
JLabel newCost = new JLabel("Cost: ", JLabel.CENTER);
JLabel newExp = new JLabel("Expense: ", JLabel.CENTER);
add(newName, Box.createHorizontalGlue());
add(newDate, Box.createHorizontalGlue());
add(newCost, Box.createHorizontalGlue());
add(newExp, Box.createHorizontalGlue());
}
另一种可能的解决方案是保留exp JPanel，但是使用getter方法将其提升为实例字段，然后不要让ExpensesPanel扩展JPanel。两者都可以工作，后者有一些优点，应该在以后讨论（关于使用组合而不是继承的优点）。
顺便说一句，这不会做任何事情：
public void paintComponent(Graphics g){
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setBackground(Color.BLUE);
}
因为在更改其Color状态后，您永远不会使用g2d绘制或清除（clearRect(...)实际上）。
更好，更容易调用构造函数：
setBackground(Color.blue);
问题接下来，这是错误的：
add(newCost, Box.createHorizontalGlue());
那不是你添加胶水的方式。请检查这方面的教程和API - 您正在进行大量的猜测工作，这些工作永远无效。
答案 1 :(得分：1)
除了@Hovercraft Full Of Eels的答案之外，您还应该通过以下方式对GUI组件进行更改...
EventQueue.invokeLater(new Runnable(){
public void run()
{
//make gui change here
}
});
这会从事件调度线程（EDT）更新它。