For 循环未使用 Java 中的 ListSelectionListener 获取正确的用户选择

Question

我正在尝试在 ListSelectionListener 事件中使用 for 循环来构建要设置为 Jlabel 的字符串。它的工作原理是，它将构建字符串并且 JLabel 将更新但不会更新用户 selected 的项目。例如，我在程序中 select “冰岛”，但程序会 select 美国，因为它是第一个索引，然后如果我继续 select 其他索引，它会到索引 1、2 等而不是我选择的那些。这是代码。

public class guiMain {
    
    private static void constructGUI() {
        JFrame.setDefaultLookAndFeelDecorated(true);
        GUI frame = new GUI();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
          SwingUtilities.invokeLater(new Runnable() {            
              public void run() {                
                 constructGUI();           
                  }        
              });
        }
}
class MyActionListener implements ActionListener {
    GUI fr;
    public MyActionListener(GUI frame) {
        fr = frame;
    }
      public void actionPerformed(ActionEvent e) {
          JComboBox cb = (JComboBox) e.getSource();
          String selection = (String) cb.getItemAt(cb.getSelectedIndex());
          System.out.println(selection);
          if(selection.contentEquals("Multiple")) { //user choice of selecting "Single" or "Multiple" in JList
              fr.ctryJList.setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);
          }
          else {
              fr.ctryJList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
          }
      }
}

    class GUI extends JFrame {
        
          public JLabel userSelected;
          public JList ctryJList;
        
          public GUI() {
              super("The Country Combo");
              init();
          }
        
          private void init() {
              //array for country choices
              String[] countries = {"United States of America", "Italy", "England", "Iceland", "Netherlands", 
                    "Sweden", "Switzerland", "Canada", "New Zealand"};
              //array for choice of selecting one, or multiple countries
              String[] selection = {"Single", "Multiple"};
              
              this.setLayout(new BorderLayout());
              this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
              JComboBox comboBox = new JComboBox(selection); //creation of ComboBox
              comboBox.addActionListener(new MyActionListener(this));
              userSelected = new JLabel("Selected items will appear here");
              ctryJList = new JList(countries); //creation of JList
              ctryJList.getSelectionModel().addListSelectionListener(new ListSelectionListener() {
                  @Override
                  public void valueChanged(ListSelectionEvent e){
                        ListSelectionModel lst = (ListSelectionModel) e.getSource();
                        int[] selectedIndices = ctryJList.getSelectedIndices();
                        String output = "Selected Items: ";
                        for(int i = 0; i < selectedIndices.length; i++) {
                            output = output + (String)ctryJList.getModel().getElementAt(i) + " ";
                            userSelected.setText(output);
                        }
                        System.out.println("Your countries are: " + output);
                  }
              });
              this.pack();
              JComponent panel = new JPanel();
              panel.setLayout(new FlowLayout());
              panel.add(new JLabel("Choose Selection Mode:"));
              panel.add(comboBox);
              this.getContentPane().add(panel,BorderLayout.NORTH);
              this.getContentPane().add(ctryJList,BorderLayout.WEST);
              this.getContentPane().add(userSelected, BorderLayout.SOUTH);
              this.pack();
              //TODO: Create JLabel for selection
          }
    }

Answer 1

output = output + (String)ctryJList.getModel().getElementAt(i) ...

您正在获取索引 0、1、2... 处的值，因为“i”始终从 0 开始。

您需要所选项目的索引，因此您需要从数组中获取索引：

output = output + (String)ctryJList.getModel().getElementAt(selectedindices[i]) ...

另外，不要使用字符串连接来构建输出字符串。而是使用 StringBuffer 或 StringBuilder 并使用 append(...) 方法。或者也许使用 StringJoiner.

For 循环未使用 Java 中的 ListSelectionListener 获取正确的用户选择

For loop not grabbing the correct user selection using ListSelectionListener in Java

java

swing

event-handling

listselectionlistener