java - 逻辑错误或重新绘制/重新验证 Java JFrame

Question

我想做的是， 当我输入详细信息时，它将在按下按钮时验证 textFiled 是否为空，如果它为空，它将显示一条消息说明。 然后它将移动到下一个文本文件，类似于许多基于 Web 的注册表单， 我想知道的是为什么消息不会改变？

将此代码粘贴到 ecilpse 文件中并运行它应该会显示简单的框架以及我正在尝试执行的操作。

当名字字段为空时，消息显示在框架底部， 谁能解释为什么当名字字段包含文本而中间名不包含文本时它不显示下一条消息？

大部分逻辑都在代码的底部。

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Toolkit;
import javax.swing.JFrame;
import javax.swing.JMenuBar;
import javax.swing.JMenu;
import javax.swing.JMenuItem;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.Color;
import javax.swing.UIManager;
import javax.swing.JPanel;
import com.jgoodies.forms.layout.FormLayout;
import com.jgoodies.forms.layout.ColumnSpec;
import com.jgoodies.forms.layout.RowSpec;
import com.jgoodies.forms.factories.FormFactory;
import javax.swing.JLabel;
import javax.swing.JTextField;
import java.awt.Font;
import javax.swing.SwingConstants;
import javax.swing.JRadioButton;
import java.awt.event.ItemListener;
import java.awt.event.ItemEvent;
import javax.swing.JButton;
import javax.swing.JComboBox;

public class start {

private JFrame frame;
private JTextField tfFirstname;
private JTextField tfMiddlenames;
private JTextField tfSurname;

/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                start window = new start();
                window.frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the application.
 */
public start() {
    initialize();
}

/**
 * Initialize the contents of the frame.
 */
private void initialize() {
    frame = new JFrame();

    frame.setBounds(100, 100, 505, 429);

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);


    frame.getContentPane().setLayout(null);

    final JPanel panelClientNew = new JPanel();
    panelClientNew.setBackground(new Color(0, 102, 255));
    panelClientNew.setBounds(10, 11, 469, 299);
    frame.getContentPane().add(panelClientNew);
    panelClientNew.setLayout(null);

    JLabel lblFirstname = new JLabel("Firstname :");
    lblFirstname.setHorizontalAlignment(SwingConstants.RIGHT);
    lblFirstname.setVerticalAlignment(SwingConstants.BOTTOM);
    lblFirstname.setForeground(new Color(255, 255, 255));
    lblFirstname.setFont(new Font("Tahoma", Font.BOLD, 13));
    lblFirstname.setBounds(10, 16, 163, 14);
    panelClientNew.add(lblFirstname);

    tfFirstname = new JTextField();
    tfFirstname.setFont(new Font("Tahoma", Font.PLAIN, 13));
    tfFirstname.setBounds(177, 10, 282, 27);
    panelClientNew.add(tfFirstname);
    tfFirstname.setColumns(10);

    JLabel lblMiddlenames = new JLabel("Middlenames :");
    lblMiddlenames.setHorizontalAlignment(SwingConstants.RIGHT);
    lblMiddlenames.setForeground(new Color(255, 255, 255));
    lblMiddlenames.setFont(new Font("Tahoma", Font.BOLD, 13));
    lblMiddlenames.setBounds(10, 47, 163, 14);
    panelClientNew.add(lblMiddlenames);

    tfMiddlenames = new JTextField();
    tfMiddlenames.setFont(new Font("Tahoma", Font.PLAIN, 13));
    tfMiddlenames.setBounds(177, 41, 282, 27);
    panelClientNew.add(tfMiddlenames);
    tfMiddlenames.setColumns(10);

    JLabel lblSurname = new JLabel("Surname :");
    lblSurname.setHorizontalAlignment(SwingConstants.RIGHT);
    lblSurname.setForeground(new Color(255, 255, 255));
    lblSurname.setFont(new Font("Tahoma", Font.BOLD, 13));
    lblSurname.setBounds(10, 78, 163, 14);
    panelClientNew.add(lblSurname);

    tfSurname = new JTextField();
    tfSurname.setFont(new Font("Tahoma", Font.PLAIN, 13));
    tfSurname.setBounds(177, 72, 282, 27);
    panelClientNew.add(tfSurname);
    tfSurname.setColumns(10);



    JButton btnAdd = new JButton("Add");
    btnAdd.addMouseListener(new MouseAdapter() {
        @Override
        public void mousePressed(MouseEvent arg0) {
            /*
             * 
             * 
             *
             *I am trying to create a message that validates on certain circumstances
             * 
             * 
             * 
             */

            if(tfFirstname.getText().equals(null) || tfFirstname.getText().equals("") || tfFirstname.getText().equals(false)) {
                JPanel panelMessage = new JPanel();
                panelMessage.setBackground(new Color(30, 144, 255));
                panelMessage.setBounds(10, 321, 469, 29);
                frame.getContentPane().add(panelMessage);

                JLabel lblPersonSaved = new JLabel("Please Enter Firstname :");
                lblPersonSaved.setForeground(new Color(255, 255, 255));
                lblPersonSaved.setFont(new Font("Tahoma", Font.BOLD, 15));
                panelMessage.add(lblPersonSaved);
                frame.revalidate();
                panelMessage.revalidate();
                frame.repaint();

            }
            else if (tfMiddlenames.getText().equals(null) || tfMiddlenames.getText().equals("") || tfMiddlenames.getText().equals(false)) {
                JPanel panelMessage = new JPanel();
                panelMessage.setBackground(new Color(30, 144, 255));
                panelMessage.setBounds(10, 321, 469, 29);
                frame.getContentPane().add(panelMessage);

                JLabel lblPersonSaved = new JLabel("Please Enter Middlenames :");
                lblPersonSaved.setForeground(new Color(255, 255, 255));
                lblPersonSaved.setFont(new Font("Tahoma", Font.BOLD, 15));
                panelMessage.add(lblPersonSaved);

                frame.revalidate();
                panelMessage.revalidate();
                frame.repaint();

            }
            else if (tfSurname.getText().equals(null) || tfSurname.getText().equals("") || tfSurname.getText().equals(false)) {
                JPanel panelMessage = new JPanel();
                panelMessage.setBackground(new Color(30, 144, 255));
                panelMessage.setBounds(10, 321, 469, 29);
                frame.getContentPane().add(panelMessage);

                JLabel lblPersonSaved = new JLabel("Please Enter Surname :");
                lblPersonSaved.setForeground(new Color(255, 255, 255));
                lblPersonSaved.setFont(new Font("Tahoma", Font.BOLD, 15));
                panelMessage.add(lblPersonSaved);
                frame.revalidate();
                panelMessage.revalidate();
                frame.repaint();

            }
            else {


                //Validation has passed

            }
        }
    });
    btnAdd.setBounds(370, 265, 89, 23);
    panelClientNew.add(btnAdd);





}
}

Answer 1

我建议您使用 InputVerifier，因为这将在允许您离开 JTextField 之前验证 JTextField 的内容是否正确(您希望定义它的任何方式)。现在它不会阻止您按其他 JButton 和诸如此类的东西，因此如果您有提交按钮，则需要采取其他预防措施。下面显示了一个检查 JTextField 是否为空的简单 InputVerifier 示例:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

@SuppressWarnings("serial")
public class InputVerifierExample extends JPanel {
   public static final Color WARNING_COLOR = Color.red;
   private JTextField firstNameField = new JTextField(10);
   private JTextField middleNameField = new JTextField(10);
   private JTextField lastNameField = new JTextField(10);
   private JTextField[] nameFields = { 
         firstNameField, 
         middleNameField,
         lastNameField };
   private JLabel warningLabel = new JLabel("  ");

   public InputVerifierExample() {
      warningLabel.setOpaque(true);

      JPanel namePanel = new JPanel();
      namePanel.add(new JLabel("Name:"));
      MyInputVerifier verifier = new MyInputVerifier();
      for (JTextField field : nameFields) {
         field.setInputVerifier(verifier);
         namePanel.add(field);
      }
      namePanel.add(new JButton(new SubmitBtnAction()));

      setLayout(new BorderLayout());
      add(namePanel, BorderLayout.CENTER);
      add(warningLabel, BorderLayout.SOUTH);
   }

   private class SubmitBtnAction extends AbstractAction {
      public SubmitBtnAction() {
         super("Submit");
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         // first check all fields aren't empty
         for (JTextField field : nameFields) {
            if (field.getText().trim().isEmpty()) {
               return;  // return if empty
            }
         }
         String name = "";
         for (JTextField field : nameFields) {
            name += field.getText() + " ";
            field.setText("");
         }
         name = name.trim();
         JOptionPane.showMessageDialog(InputVerifierExample.this, name, "Name Entered",
               JOptionPane.INFORMATION_MESSAGE);
      }
   }

   private class MyInputVerifier extends InputVerifier {

      @Override
      public boolean verify(JComponent input) {
         JTextField field = (JTextField) input;
         if (field.getText().trim().isEmpty()) {
            warningLabel.setText("Please do not leave this field empty");
            warningLabel.setBackground(WARNING_COLOR);
            return false;
         }
         warningLabel.setText("");
         warningLabel.setBackground(null);
         return true;
      }

   }

   private static void createAndShowGui() {
      JFrame frame = new JFrame("InputVerifier Example");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(new InputVerifierExample());
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}