我在添加卡片布局时遇到了困难。我在这里分享我的代码。
package LoginUser;
import java.awt.*;
import javax.swing.UIManager;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.*;
import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;
import DBconnection.SelectTable;
import DBconnection.TestConnection;
import GUITTG.Branch;
import GUITTG.TTGFrame;
import javax.swing.border.LineBorder;
import javax.swing.border.TitledBorder;
public class LoginForm extends JFrame implements ActionListener
{
private static final long serialVersionUID = 1L;
char ch;
//Container con1;
JPanel jpanelMainMain,jpanelMain,jpanelMainC;
JPanel jpanelMainC1,jpanelMainC2,jpanelMainC3;
JPanle jpanelMainC4,jpanelMainC5,jpanelMainC6;
CardLayout cardLayout;
JButton login,register;
JLabel id,pass;
JTextField idtxt;
Font font;
JPasswordField pw;
RegisterForm rf;
TestConnection tb;
SelectTable stble;
Statement st;
Connection con;
ResultSet rs;
TTGFrame ttg;
Container con1;
public LoginForm()
{
UIManager.getLookAndFeelDefaults().put("ClassLoader", this.getClass().getClassLoader());
this.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
setBackground(new Color(0 ,0 ,0));
con1=getContentPane();
cardLayout=new CardLayout();
jpanelMainMain=new JPanel(cardLayout);
font=new Font("title",Font.PLAIN,20);
id=new JLabel("Login Id:");
id.setFont(font);
id.setForeground(Color.WHITE);
pass=new JLabel("Password:");
pass.setFont(font);
pass.setForeground(Color.WHITE);
idtxt=new JTextField();
pw=new JPasswordField();
login=new JButton("Login");
register=new JButton("Register");
jpanelMain=new JPanel(new BorderLayout());
jpanelMain.setBorder(new TitledBorder(new LineBorder(new Color(0 ,0 ,0)), "Login Form", 0, 0, font, new Color(0 ,0 ,0)));
jpanelMain.add(new JLabel() ,BorderLayout.SOUTH);
/* jpanelMainC1=new JPanel(new BorderLayout());
jpanelMainC1.add(id);
jpanelMainC2=new JPanel(new BorderLayout());
jpanelMainC2.add(pass);
jpanelMainC3=new JPanel(new BorderLayout());
jpanelMainC3.add(idtxt);
jpanelMainC4=new JPanel(new BorderLayout());
jpanelMainC4.add(pw);
jpanelMainC5=new JPanel(new BorderLayout());
jpanelMainC5.add(login);
jpanelMainC6=new JPanel(new BorderLayout());
jpanelMainC6.add(register);
*/
jpanelMainC=new JPanel(new BorderLayout());
jpanelMainC.add(id);
jpanelMainC.add(pass);
jpanelMainC.add(idtxt);
jpanelMainC.add(pw);
jpanelMainC.add(login);
jpanelMainC.add(register);
/*jpanelMainC=new JPanel(new BorderLayout());
jpanelMainC.add(jpanelMainC1);
jpanelMainC.add(jpanelMainC2);
jpanelMainC.add(jpanelMainC3);
jpanelMainC.add(jpanelMainC4);
jpanelMainC.add(jpanelMainC5);
jpanelMainC.add(jpanelMainC6);*/
jpanelMain.add(jpanelMainC ,BorderLayout.CENTER);
jpanelMainC.setBackground(new Color(0,150,150));
jpanelMainMain.setBackground(new Color(0,150,150));
add(id);
add(pass);
add(idtxt);
add(pw);
add(login);
add(register);
con1.setLayout(null);
con1.setBackground(new Color(0,150,150));
id.setBounds(100,100,100,30);
pass.setBounds(100,150,100,20);
idtxt.setBounds(210,100,100,20);
pw.setBounds(210,150,100,20);
login.setBounds(100,200,100,20);
register.setBounds(210,200,100,20);
login.addActionListener(this);
register.addActionListener(this);
// con1.add(jpanelMain);
jpanelMainMain.add(jpanelMain);
cardLayout.show(jpanelMainMain ,"LoginForm");
tb=new TestConnection();
idtxt.addKeyListener(new KeyAdapter()
{
public void keyTyped(KeyEvent ke)
{
char c = ke.getKeyChar();
if (!((c >= '0') && (c <= '9') ||(c == KeyEvent.VK_BACK_SPACE) ||
(c == KeyEvent.VK_DELETE)))
{
getToolkit().beep();
ke.consume();
}
}
});
pw.addKeyListener(new KeyAdapter()
{
public void keyTyped(KeyEvent ke)
{
char c = ke.getKeyChar();
if (((c >= '0') && (c <= '9') ||(c == KeyEvent.VK_BACK_SPACE) ||
(c == KeyEvent.VK_DELETE)))
{
getToolkit().beep();
ke.consume();
}
}
});
}
public void setLookAndFeel(String name)
{
if(name == null)
{
return;
}
try
{
UIManager.setLookAndFeel(name);
}
catch(Exception ex)
{
javax.swing.JOptionPane.showMessageDialog(this, ex.getMessage());
}
}
public void actionPerformed(ActionEvent ae)
{
int cnt=0;
if(ae.getSource()==login)
{
try
{
con=tb.getConnection();
st=tb.getStatement();
stble=new SelectTable(st);
stble.getConnWithTable("login_table");
rs=stble.getResultSet();
String i=idtxt.getText();
String p=pw.getText();
while(rs.next())
{
if(rs.getString(1).equals(i)&&rs.getString(2).equals(p))
cnt=1;
}
}
catch(Exception e){}
if(cnt==1)
{
JOptionPane.showMessageDialog(this,"Login Success......");
ttg=new TTGFrame();
ttg.setTitle("Time Table Application.TTG Frame Form");
ttg.setVisible(true);
setVisible(false);
}
else
{
JOptionPane.showMessageDialog(this,"Login Fail......try again?");
idtxt.setText("");
pw.setText("");
}
}
else
{
rf=new RegisterForm();
rf.setTitle("Time Table Application.Registration Form");
rf.setSize(1000,1000);
rf.setVisible(true);
setVisible(false);
}
}
public JPanel getMyJPanel()
{
return jpanelMain;
}
public String getMyName()
{
return "LoginForm";
}
public static void main(String args[]) throws Exception
{
LoginForm l=new LoginForm();
l.setTitle("Time Table Application.Login Form");
l.setSize(500,500);
l.setResizable(false);
l.setVisible(true);
//this.setTitle("Time-Table Application.Branch");
//setVisible(true);
}
}
class WindowUtilities
{
/** Tell system to use native look and feel, as in previous
* releases. Metal (Java) LAF is the default otherwise.
*/
public static void setNativeLookAndFeel()
{
try
{
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
}
catch(Exception e)
{
System.out.println("Error setting native LAF: " + e);
}
}
public static void setJavaLookAndFeel()
{
try
{
UIManager.setLookAndFeel(UIManager.getCrossPlatformLookAndFeelClassName());
}
catch(Exception e)
{
System.out.println("Error setting Java LAF: " + e);
}
}
public static void setMotifLookAndFeel()
{
try
{
UIManager.setLookAndFeel("com.sun.java.swing.plaf.motif.MotifLookAndFeel");
}
catch(Exception e)
{
System.out.println("Error setting Motif LAF: " + e);
}
}
/** A simplified way to see a JPanel or other Container.
* Pops up a JFrame with specified Container as the content pane.
*/
public static JFrame openInJFrame(Container content, int width, int height, String title, Color bgColor)
{
JFrame frame = new JFrame(title);
frame.setBackground(bgColor);
content.setBackground(bgColor);
frame.setSize(width, height);
frame.setContentPane(content);
frame.setVisible(true);
return(frame);
}
/** Uses Color.white as the background color. */
public static JFrame openInJFrame(Container content, int width, int height, String title)
{
return(openInJFrame(content, width, height, title, Color.white));
}
/** Uses Color.white as the background color, and the
* name of the Container's class as the JFrame title.
*/
public static JFrame openInJFrame(Container content, int width, int height)
{
return(openInJFrame(content, width, height, content.getClass().getName(), Color.white));
}
}
我遇到以下异常：
线程“main”中的异常java.lang.IllegalArgumentException：无法添加到
layout：约束必须是字符串
at java.awt.CardLayout.addLayoutComponent(Unknown Source)
at java.awt.Container.addImpl(Unknown Source)
at java.awt.Container.add(Unknown Source)
at LoginUser.LoginForm.<init>(LoginForm.java:158)
at LoginUser.LoginForm.main(LoginForm.java:277)
答案 0 :(得分：0)
线程“main”中的异常java.lang.IllegalArgumentException：无法添加到 layout：约束必须是字符串
jpanelMainMain.add(jpanelMain);
消息似乎很直接。使用CardLayout将组件添加到面板时，未指定String约束。
cardLayout.show(jpanelMainMain ,"LoginForm");
如果在将面板添加到CardLayout时未指定约束，CardLayout如何知道哪个面板是“LoginForm”？
阅读How to Use CardLayout上Swing教程中的部分，了解一些工作示例，向您展示如何在向CardLayout添加面板时指定约束。它还显示了如何通过指定约束来交换面板。