无法让我的 jcombobox getSelectedItem() 正常工作。尝试将其分配给一个变量以在 if/else 语句中使用

Question

问题部分是我声明和分配的地方：

String emotionText = (String) emotions.getSelectedItem();

我稍后尝试使用它来与 JcomboBox 中的数组项之一进行比较。我说的地方

if (emotionText.equals("Happy") {
    JLabel newText = new JLabel(verse);
    panel2.add(newText);
}

即。如果结果是这样..那么就这样做，但它不能正常工作。任何见解将不胜感激。预先感谢。

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

public class GUI extends JComboBox {

    public static void main(String[] args) {
        JFrame frame = new JFrame("Mood Food");
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(900, 800);
        frame.setLocation(430, 100);

        JPanel panel = new JPanel();
        panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS)); // added code

        frame.add(panel);
        var name = javax.swing.JOptionPane.showInputDialog("What is your name?");

        JLabel lblName = new JLabel(name + " ,welcome to the Mood Food Program");
        lblName.setAlignmentX(Component.CENTER_ALIGNMENT);
        panel.add(lblName);

        JLabel lbl = new JLabel("How are you feeling today?");
        lbl.setAlignmentX(Component.CENTER_ALIGNMENT);
        panel.add(lbl);


        String[] choices = {"Select..", "Happy", "Content", "Grateful", "Excited", "Sad",
                "Angry", "Lonely", "Heartbroken", "Worried"};

        JComboBox<String> emotions = new JComboBox<String>(choices);
        emotions.setMaximumSize(panel.getPreferredSize());
        emotions.setAlignmentX(Component.CENTER_ALIGNMENT);
        emotions.setAlignmentY(Component.TOP_ALIGNMENT);
        String emotionText = (String) emotions.getSelectedItem();

        panel.add(emotions);

        String verse = Happy.Verses();

        JPanel panel2 = new JPanel();
        panel2.setVisible(false);
        frame.add(panel2);

if (emotionText.equals("Happy") {
    JLabel newText = new JLabel(verse);
    panel2.add(newText);
}


        JButton btn = new JButton("OK");
        btn.setAlignmentX(Component.CENTER_ALIGNMENT); // added code
        panel.add(btn);
        btn.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e){
                boolean visible = panel.isVisible();
                panel.setVisible(!visible);
                panel2.setVisible(visible);
                }});

        frame.setVisible(true); // added code

    }
}

Answer 1

Swing 是一个事件驱动的环境，也就是说，发生某些事情并且您对其做出响应。这也意味着您的代码不会以线性或顺序流运行。

例如，你不能这样做...

JComboBox<String> emotions = new JComboBox<String>(choices);
emotions.setMaximumSize(panel.getPreferredSize());
emotions.setAlignmentX(Component.CENTER_ALIGNMENT);
emotions.setAlignmentY(Component.TOP_ALIGNMENT);
String emotionText = (String) emotions.getSelectedItem();

panel.add(emotions);

String verse = Happy.Verses();

if (emotionText.equals("Happy") {
    JLabel newText = new JLabel(verse);
    panel2.add(newText);
}

当您调用

getSelectedItem

时，用户实际上没有机会选择任何内容（没有向他们呈现任何内容）。

相反，您需要将

ActionListener

添加到

JComboBox

并从其中更新

emotionText

。

由于此工作流程的延迟性质，您还应该更新按钮上的

ActionListener

，以根据

emotionText

的值更新标签。

更像是...

import java.awt.CardLayout;
import java.awt.Component;
import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class Main extends JComboBox {

    public static void main(String[] args) {
        new Main();
    }

    private String emotionText = "Empty inside";
    private CardLayout cardLayout;

    public Main() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame("Mood Food");
                frame.setVisible(true);
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setSize(900, 800);
                frame.setLocation(430, 100);

                cardLayout = new CardLayout();
                frame.setLayout(cardLayout);

                JPanel panel = new JPanel();
                panel.setLayout(new GridBagLayout());

                GridBagConstraints gbc = new GridBagConstraints();
                gbc.gridwidth = GridBagConstraints.REMAINDER;

                frame.add(panel, "first");
                var name = javax.swing.JOptionPane.showInputDialog("What is your name?");

                JLabel lblName = new JLabel(name + " ,welcome to the Mood Food Program");
                lblName.setAlignmentX(Component.CENTER_ALIGNMENT);
                panel.add(lblName, gbc);

                JLabel lbl = new JLabel("How are you feeling today?");
                lbl.setAlignmentX(Component.CENTER_ALIGNMENT);
                panel.add(lbl, gbc);

                String[] choices = {"Select..", "Happy", "Content", "Grateful", "Excited", "Sad",
                    "Angry", "Lonely", "Heartbroken", "Worried"};

                JComboBox<String> emotions = new JComboBox<String>(choices);
                emotions.addActionListener(new ActionListener() {
                    @Override
                    public void actionPerformed(ActionEvent e) {
                        emotionText = (String)emotions.getSelectedItem();
                    }
                });

                panel.add(emotions, gbc);

                JPanel panel2 = new JPanel();
                JLabel newText = new JLabel(emotionText);
                panel2.add(newText);

                frame.add(panel2, "second");

                JButton btn = new JButton("OK");
                btn.setAlignmentX(Component.CENTER_ALIGNMENT); // added code
                panel.add(btn, gbc);
                btn.addActionListener(new ActionListener() {
                    public void actionPerformed(ActionEvent e) {
                        newText.setText(emotionText);
                        cardLayout.show(frame.getContentPane(), "second");
                    }
                });

                frame.setVisible(true); // added code            
            }
        });
    }
}