java - 将监听器与列表和按钮一起使用

Question

对 Java 很陌生，但我正在慢慢地寻找自己的方法。所以请善待。我理解到目前为止我尝试过的大多数事情，并构建了以下使用控制台输出的版本，但现在我正在尝试制作一个 GUI。我尝试了 netbeans GUI maker，但它创建了太多新代码，以至于当我试图挑选它时，我迷路了。我更擅长通过自己拼凑新事物来学习，而不是让 IDE 生成大量代码，然后尝试找到我想工作的地方。

我正在尝试构建一个窗口，该窗口的左侧有一个包含三个选项的列表，中间有一个确认您的选择的按钮，右侧有一个答案输出。按下按钮后，将读取列表中的输入并将其转换为相应的答案。截至目前，在列表中选择一个选项后，我得到的只是“We recommend...null”。该按钮目前似乎什么都不做。

我已经使用了教程，从网上破解了别人的代码，并引用了几本书，但我被卡住了。

这是我的:

package diffguidegui;

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


public class DiffGuideGUI extends JPanel implements ListSelectionListener {

    private JList resultsTabList;
    private DefaultListModel listModel;
    private static final String recommendString = "Recommend a Option";
    private JButton recommendButton;
    private String recommendOutput;
    final JLabel output = new JLabel("We recommend..." + recommendOutput); 

    //build list
    public DiffGuideGUI () {
        super(new BorderLayout());
        listModel = new DefaultListModel();
        listModel.addElement("A");
        listModel.addElement("B");

        //create the list and put it in the scroll pane
        resultsTabList = new JList(listModel);
        resultsTabList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        resultsTabList.setSelectedIndex(0);
        //listener for user input
        resultsTabList.addListSelectionListener(this);
        resultsTabList.setVisibleRowCount(2);
        JScrollPane listScrollPane = new JScrollPane(resultsTabList);

        //build the button at the bottom to fire overall behavior
        recommendButton = new JButton(recommendString);
        recommendButton.setActionCommand(recommendString);
        recommendButton.addActionListener(new RecommendListener());

        //create a panel that uses Boxlayout for the button
        JPanel buttonPane = new JPanel();
        buttonPane.setLayout(new BoxLayout(buttonPane, BoxLayout.LINE_AXIS));
        buttonPane.add(recommendButton);

        //create a panel that uses Boxlayout for the label
        JPanel outputPane = new JPanel();
        outputPane.setLayout(new BoxLayout(outputPane, BoxLayout.LINE_AXIS));
        outputPane.add(output);

        add(listScrollPane, BorderLayout.WEST);
        add(buttonPane, BorderLayout.CENTER);
        add(outputPane, BorderLayout.EAST);
    }


    //build listener class
    class RecommendListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {

            //build in logic for choice made here
            String resultsTabChoice;
            resultsTabChoice = (String)resultsTabList.getSelectedValue();

            if( resultsTabChoice.equals("A")) {
                recommendOutput = "One";}
            else {recommendOutput = "Two";}
        }
    }


    public void valueChanged(ListSelectionEvent e) {
        if(e.getValueIsAdjusting() == false) {

            if(resultsTabList.getSelectedIndex() == -1) {
                recommendButton.setEnabled(false);
            } else {
                recommendButton.setEnabled(true);
            }
        }
    }

    //Create GUI and show it
    private static void createAndShowGUI() {
        JFrame frame = new JFrame("Recommend Window");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);


        //create and set up content pane
        JComponent newContentPane = new DiffGuideGUI();
        newContentPane.setOpaque(true);
        frame.setContentPane(newContentPane);

        //display the window
        frame.pack();
        frame.setVisible(true);
    }

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

}

Answer 1

The button appears to do nothing at the moment.

它做 一些事情。它计算您的 recommendOutput 变量的值。但是你永远不会输出这个值。

尝试以下操作:

 //build listener class
 class RecommendListener implements ActionListener {
     public void actionPerformed(ActionEvent e) {
        //build in logic for choice made here
        String resultsTabChoice;
        resultsTabChoice = (String)resultsTabList.getSelectedValue();

        if( resultsTabChoice.equals("A")) {
            recommendOutput = "One";}
        else {recommendOutput = "Two";}
        System.out.println(recommendOutput); // <-###################
    }
}

这应该将值打印到标准输出

要将值放入您的标签中，请尝试以下操作:

output.setText(recommendOutput);