JLabel 不会在按钮单击时显示答案

【问题标题】：JLabel wont show up on button clickJLabel 不会在按钮单击时显示
【发布时间】：2021-07-29 17:25:42
【问题描述】：

这是我的第一个 GUI，所以任何建议在这里都是很好的建议，但主要是我只是想弄清楚为什么我的 errorLabel 不会出现。我试过setVisible、setOpaque，手动设置位置，最后（如下所示）只是让它自己的面板坐下来，它仍然不会显示在按钮按下。

有什么想法吗？

package GUI;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import javax.swing.*;


/**
 *
 * @author User
 */
public class AddChair extends JFrame {

    private final int FRAME_HEIGHT = 600;
    private final int FRAME_WIDTH = 400;
    private final String ADD_CHAIR_TITLE = "Chair";
    private final int TEXT_BOX_WIDTH = FRAME_WIDTH / 4;
    private final int TEXT_BOX_HEIGHT = 25;

    private JPanel basePanel;
    private JPanel leftPanel;
    private JPanel rightPanel;
    private JPanel lowerPanel;
    private JPanel itemIDPanel;
    private JPanel woodTypePanel;
    private JPanel armrestPanel;
    private JPanel quantityPanel;
    private JPanel itemIDInputPanel;
    private JPanel woodTypeInputPanel;
    private JPanel quantityInputPanel;
    private JPanel armrestInputPanel;
    private JPanel confirmCancelPanel;
    private JPanel errorPanel;

    private JTextField itemIDTextField;
    private JTextField quantityTextField;

    private JRadioButton walnut;
    private JRadioButton oak;
    private JRadioButton yes;
    private JRadioButton no;
    
    private JButton confirmButton;
    private JButton cancelButton;

    public AddChair() {
        frameSetup();
        add(basePanel());
    }

    private void frameSetup() {   // sets up base frame
        setSize(FRAME_WIDTH, FRAME_HEIGHT);
        setVisible(true);
        setAlwaysOnTop(true);
        setTitle(ADD_CHAIR_TITLE);
        setLocationRelativeTo(null);
    }

    private JPanel basePanel() {   //sets up a base panel to arrange other panels on
        basePanel = new JPanel(new BorderLayout());
        basePanel.setPreferredSize(new Dimension(FRAME_WIDTH, FRAME_HEIGHT));
        basePanel.add(leftPanel(), BorderLayout.WEST);
        basePanel.add(rightPanel(), BorderLayout.EAST);
        basePanel.add(lowerPanel(), BorderLayout.SOUTH);
        return basePanel;
    }

    private JPanel leftPanel() {   //sets up the left panel which will contain labels
        leftPanel = new JPanel();
        leftPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4));
        leftPanel.setVisible(true);
        labelPanels();
        labels();
        return leftPanel;
    }

    private void labelPanels() {//sets up the panels for the labels
        itemIDPanel = new JPanel();
        woodTypePanel = new JPanel();
        armrestPanel = new JPanel();
        quantityPanel = new JPanel();

        itemIDPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));
        woodTypePanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));
        armrestPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));
        quantityPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));

        itemIDPanel.setVisible(true);
        woodTypePanel.setVisible(true);
        armrestPanel.setVisible(true);
        quantityPanel.setVisible(true);

        leftPanel.add(itemIDPanel);
        leftPanel.add(woodTypePanel);
        leftPanel.add(armrestPanel);
        leftPanel.add(quantityPanel);
    }

    private void labels() {   //sets up the and adds the labels for the user 
        JLabel itemIDLabel = new JLabel("Item ID:");
        JLabel woodTypeLabel = new JLabel("Wood Type:");
        JLabel armrestLabel = new JLabel("Armrest:");
        JLabel quantityLabel = new JLabel("Quantity:");

        itemIDLabel.setVisible(true);
        woodTypeLabel.setVisible(true);
        armrestLabel.setVisible(true);
        quantityLabel.setVisible(true);

        itemIDPanel.add(itemIDLabel);
        woodTypePanel.add(woodTypeLabel);
        armrestPanel.add(armrestLabel);
        quantityPanel.add(quantityLabel);
    }

    private JPanel rightPanel() {   // sets up the right panel which will contain the user input objects
        rightPanel = new JPanel();
        rightPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4));
        rightPanel.setVisible(true);
        userInputPanels();
        return rightPanel;
    }

    private void userInputPanels() {//sets up the panels for the labels
        itemIDInputPanel = new JPanel();
        woodTypeInputPanel = new JPanel();
        armrestInputPanel = new JPanel();
        quantityInputPanel = new JPanel();

        itemIDInputPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));
        woodTypeInputPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));
        armrestInputPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));
        quantityInputPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));

        itemIDInputPanel.setVisible(true);
        woodTypeInputPanel.setVisible(true);
        armrestInputPanel.setVisible(true);
        quantityInputPanel.setVisible(true);

        userInputs();

        rightPanel.add(itemIDInputPanel);
        rightPanel.add(woodTypeInputPanel);
        rightPanel.add(armrestInputPanel);
        rightPanel.add(quantityInputPanel);
    }

    private void userInputs() {   // sets up and adds to the right panel the user input objects
        itemIDTextField = new JTextField("");
        walnut = new JRadioButton("Walnut");
        oak = new JRadioButton("Oak");
        yes = new JRadioButton("Yes");
        no = new JRadioButton("No");
        quantityTextField = new JTextField("");
        
        itemIDTextField.setPreferredSize(new Dimension(TEXT_BOX_WIDTH, TEXT_BOX_HEIGHT));
        itemIDInputPanel.add(itemIDTextField);

        ButtonGroup woodTypeGroup = new ButtonGroup();
        woodTypeGroup.add(oak);
        woodTypeGroup.add(walnut);
        woodTypeInputPanel.add(walnut);
        woodTypeInputPanel.add(oak);

        ButtonGroup armrestGroup = new ButtonGroup();
        armrestGroup.add(yes);
        armrestGroup.add(no);
        armrestInputPanel.add(yes);
        armrestInputPanel.add(no);

        quantityTextField.setPreferredSize(new Dimension(TEXT_BOX_WIDTH, TEXT_BOX_HEIGHT));
        quantityInputPanel.add(quantityTextField);
    }

    private JPanel lowerPanel() {   // sets up the lower panel for confirm and cancel buttons
        lowerPanel = new JPanel(new BorderLayout());
        lowerPanel.setPreferredSize(new Dimension(FRAME_WIDTH, FRAME_HEIGHT / 4));
        lowerPanel.setVisible(true);
        confirmCancelPanel();
        errorPanel();
        confirmCancelButtons();
        return lowerPanel;
    }
    
    private void confirmCancelPanel(){
        confirmCancelPanel = new JPanel();
        confirmCancelPanel.setPreferredSize(new Dimension(FRAME_WIDTH, FRAME_HEIGHT / 8));
        confirmCancelPanel.setBackground(Color.blue);
        confirmCancelPanel.setVisible(true);
        lowerPanel.add(confirmCancelPanel, BorderLayout.NORTH);
    }
    
    private void errorPanel(){
        errorPanel = new JPanel();
        errorPanel.setPreferredSize(new Dimension(FRAME_WIDTH, FRAME_HEIGHT / 8));
        errorPanel.setBackground(Color.yellow);
        errorPanel.setVisible(true);
        lowerPanel.add(errorPanel, BorderLayout.SOUTH);
    }
    
    private void confirmCancelButtons(){
        confirmButton = new JButton("Confirm");
        cancelButton = new JButton("Cancel");
        
        confirmButton.setVisible(true);
        cancelButton.setVisible(true);
        
        confirmCancelPanel.add(confirmButton);
        confirmCancelPanel.add(cancelButton);
        
        cancelButtonLogic();
        confirmButtonLogic();
    }
    
    private void cancelButtonLogic(){
        cancelButton.addActionListener((ActionEvent ae) -> {
            this.dispose();
        });
    }
    
    private void confirmButtonLogic(){
        confirmButton.addActionListener((ActionEvent ae) -> {
            errorMessage();
            
        });
    }
    
    private void errorMessage(){
        JLabel errorLabel = new JLabel("Error");
        errorLabel.setOpaque(true);
        errorLabel.setVisible(true);
        errorLabel.setForeground(Color.BLACK);
        errorPanel.add(errorLabel);
    }
}

【问题讨论】：

标签： java swing user-interface jlabel

【解决方案1】：

我添加了一个静态 main 方法，以便我可以运行 GUI。我修改了你的 errorPanel 和 errorMessage 方法。

这是启动时的 GUI。

这是左击确认JButton后的GUI。

我没有详细查看您的代码，但您似乎为表单JPanel、按钮JPanel 和错误JPanel 发布了很多代码。

这是完整的可运行代码。

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionEvent;

import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;


/**
 *
 * @author User
 */
public class AddChair extends JFrame {
    
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new AddChair();
            }
        });
    }

    private final int FRAME_HEIGHT = 600;
    private final int FRAME_WIDTH = 400;
    private final String ADD_CHAIR_TITLE = "Chair";
    private final int TEXT_BOX_WIDTH = FRAME_WIDTH / 4;
    private final int TEXT_BOX_HEIGHT = 25;
    
    private JLabel errorLabel;

    private JPanel basePanel;
    private JPanel leftPanel;
    private JPanel rightPanel;
    private JPanel lowerPanel;
    private JPanel itemIDPanel;
    private JPanel woodTypePanel;
    private JPanel armrestPanel;
    private JPanel quantityPanel;
    private JPanel itemIDInputPanel;
    private JPanel woodTypeInputPanel;
    private JPanel quantityInputPanel;
    private JPanel armrestInputPanel;
    private JPanel confirmCancelPanel;
    private JPanel errorPanel;

    private JTextField itemIDTextField;
    private JTextField quantityTextField;

    private JRadioButton walnut;
    private JRadioButton oak;
    private JRadioButton yes;
    private JRadioButton no;
    
    private JButton confirmButton;
    private JButton cancelButton;

    public AddChair() {
        frameSetup();
        add(basePanel());
    }

    private void frameSetup() {   // sets up base frame
        setSize(FRAME_WIDTH, FRAME_HEIGHT);
        setVisible(true);
        setAlwaysOnTop(true);
        setTitle(ADD_CHAIR_TITLE);
        setLocationRelativeTo(null);
    }

    private JPanel basePanel() {   //sets up a base panel to arrange other panels on
        basePanel = new JPanel(new BorderLayout());
        basePanel.setPreferredSize(new Dimension(FRAME_WIDTH, FRAME_HEIGHT));
        basePanel.add(leftPanel(), BorderLayout.WEST);
        basePanel.add(rightPanel(), BorderLayout.EAST);
        basePanel.add(lowerPanel(), BorderLayout.SOUTH);
        return basePanel;
    }

    private JPanel leftPanel() {   //sets up the left panel which will contain labels
        leftPanel = new JPanel();
        leftPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4));
        leftPanel.setVisible(true);
        labelPanels();
        labels();
        return leftPanel;
    }

    private void labelPanels() {//sets up the panels for the labels
        itemIDPanel = new JPanel();
        woodTypePanel = new JPanel();
        armrestPanel = new JPanel();
        quantityPanel = new JPanel();

        itemIDPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));
        woodTypePanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));
        armrestPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));
        quantityPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));

        itemIDPanel.setVisible(true);
        woodTypePanel.setVisible(true);
        armrestPanel.setVisible(true);
        quantityPanel.setVisible(true);

        leftPanel.add(itemIDPanel);
        leftPanel.add(woodTypePanel);
        leftPanel.add(armrestPanel);
        leftPanel.add(quantityPanel);
    }

    private void labels() {   //sets up the and adds the labels for the user 
        JLabel itemIDLabel = new JLabel("Item ID:");
        JLabel woodTypeLabel = new JLabel("Wood Type:");
        JLabel armrestLabel = new JLabel("Armrest:");
        JLabel quantityLabel = new JLabel("Quantity:");

        itemIDLabel.setVisible(true);
        woodTypeLabel.setVisible(true);
        armrestLabel.setVisible(true);
        quantityLabel.setVisible(true);

        itemIDPanel.add(itemIDLabel);
        woodTypePanel.add(woodTypeLabel);
        armrestPanel.add(armrestLabel);
        quantityPanel.add(quantityLabel);
    }

    private JPanel rightPanel() {   // sets up the right panel which will contain the user input objects
        rightPanel = new JPanel();
        rightPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4));
        rightPanel.setVisible(true);
        userInputPanels();
        return rightPanel;
    }

    private void userInputPanels() {//sets up the panels for the labels
        itemIDInputPanel = new JPanel();
        woodTypeInputPanel = new JPanel();
        armrestInputPanel = new JPanel();
        quantityInputPanel = new JPanel();

        itemIDInputPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));
        woodTypeInputPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));
        armrestInputPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));
        quantityInputPanel.setPreferredSize(new Dimension(FRAME_WIDTH / 2, FRAME_HEIGHT * 3 / 4 / 5));

        itemIDInputPanel.setVisible(true);
        woodTypeInputPanel.setVisible(true);
        armrestInputPanel.setVisible(true);
        quantityInputPanel.setVisible(true);

        userInputs();

        rightPanel.add(itemIDInputPanel);
        rightPanel.add(woodTypeInputPanel);
        rightPanel.add(armrestInputPanel);
        rightPanel.add(quantityInputPanel);
    }

    private void userInputs() {   // sets up and adds to the right panel the user input objects
        itemIDTextField = new JTextField("");
        walnut = new JRadioButton("Walnut");
        oak = new JRadioButton("Oak");
        yes = new JRadioButton("Yes");
        no = new JRadioButton("No");
        quantityTextField = new JTextField("");
        
        itemIDTextField.setPreferredSize(new Dimension(TEXT_BOX_WIDTH, TEXT_BOX_HEIGHT));
        itemIDInputPanel.add(itemIDTextField);

        ButtonGroup woodTypeGroup = new ButtonGroup();
        woodTypeGroup.add(oak);
        woodTypeGroup.add(walnut);
        woodTypeInputPanel.add(walnut);
        woodTypeInputPanel.add(oak);

        ButtonGroup armrestGroup = new ButtonGroup();
        armrestGroup.add(yes);
        armrestGroup.add(no);
        armrestInputPanel.add(yes);
        armrestInputPanel.add(no);

        quantityTextField.setPreferredSize(new Dimension(TEXT_BOX_WIDTH, TEXT_BOX_HEIGHT));
        quantityInputPanel.add(quantityTextField);
    }

    private JPanel lowerPanel() {   // sets up the lower panel for confirm and cancel buttons
        lowerPanel = new JPanel(new BorderLayout());
        lowerPanel.setPreferredSize(new Dimension(FRAME_WIDTH, FRAME_HEIGHT / 4));
        lowerPanel.setVisible(true);
        confirmCancelPanel();
        errorPanel();
        confirmCancelButtons();
        return lowerPanel;
    }
    
    private void confirmCancelPanel(){
        confirmCancelPanel = new JPanel();
        confirmCancelPanel.setPreferredSize(new Dimension(FRAME_WIDTH, FRAME_HEIGHT / 8));
        confirmCancelPanel.setBackground(Color.blue);
        confirmCancelPanel.setVisible(true);
        lowerPanel.add(confirmCancelPanel, BorderLayout.NORTH);
    }
    
    private void errorPanel(){
        errorPanel = new JPanel();
        errorPanel.setPreferredSize(new Dimension(FRAME_WIDTH, FRAME_HEIGHT / 8));
        errorPanel.setBackground(Color.yellow);
        errorPanel.setVisible(true);
        
        errorLabel = new JLabel(" ");
        errorLabel.setOpaque(true);
        errorLabel.setVisible(true);
        errorLabel.setForeground(Color.BLACK);
        errorPanel.add(errorLabel);
        
        lowerPanel.add(errorPanel, BorderLayout.SOUTH);
    }
    
    private void confirmCancelButtons(){
        confirmButton = new JButton("Confirm");
        cancelButton = new JButton("Cancel");
        
        confirmButton.setVisible(true);
        cancelButton.setVisible(true);
        
        confirmCancelPanel.add(confirmButton);
        confirmCancelPanel.add(cancelButton);
        
        cancelButtonLogic();
        confirmButtonLogic();
    }
    
    private void cancelButtonLogic(){
        cancelButton.addActionListener((ActionEvent ae) -> {
            this.dispose();
        });
    }
    
    private void confirmButtonLogic(){
        confirmButton.addActionListener((ActionEvent ae) -> {
            errorMessage();
            
        });
    }
    
    private void errorMessage(){
        errorLabel.setText("Error message");
    }
    
}

【讨论】：

谢谢，这大概是我的答案。我在错误面板的创建中创建了它，并让它在点击时可见，但是同样的事情谢谢:)

【解决方案2】：

我试过 setVisible，

Swing 组件默认是可见的。无需在组件上调用 setVisible(true)

我的 errorLabel 不会出现。

当您将组件添加到可见 GUI 时，基本代码是：

errorPanel.add(errorLabel);
errorPanel.revalidate();
errorPanel.repaint();

这将确保调用布局管理器，以便为标签指定大小/位置。

但是，另一种解决方案是在创建 GUI 时创建“errorLabel”并将其添加到“errorPanel”。您将设置设置为“”。所以标签占用了一些空间。然后，您只需调用 error.Label.setText(...) 即可使用各种错误消息更新标签。当然，这意味着标签需要定义为实例变量。

【讨论】：

感谢您的解释。正如你所说，我最终预先创建并添加了标签，效果很好，但让我摸不着头脑，为什么按钮不允许我在点击时创建标签
让我摸不着头脑，为什么按钮不允许我在点击时创建标签 - 默认情况下，组件的大小为 0，因此没有可绘制的内容.通常调用 revalidate() 和 repaint() 将解决问题。如果没有，那么您需要调用 revalidate() 并在“errorPanel”的父面板上重新绘制。