java - jcombobox 与 jbutton 一起使用

Question

我想知道如何设置与 Jbutton 一起使用的 JComboBox。在 JcomboBox 中选择某个对象会在按下按钮时更改计算。这是我到目前为止所拥有的，但它似乎不起作用，我不确定它出了什么问题。

    //JComboBox objectList = new JComboBox();
    String[] objectStrings = { "Triangle", "Box", "Done" };
    JComboBox objectList = new JComboBox(objectStrings);
    //objectList.setModel(new DefaultComboBoxModel(new String[]{"Triangle", "Box", "Done"}));
    objectList.setSelectedIndex(0);
    final int object = objectList.getSelectedIndex();
    objectList.setBounds(180, 7, 86, 20);
    objectList.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            if (object == 2) {
                System.exit(0);
            }
        }
    });



    frmPrestonPalecekWeek.getContentPane().add(objectList);

    JButton btnCalculate = new JButton("Calculate!");
    btnCalculate.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent arg0) {
            String box;
            String done;
            Box a;
            Triangle b;
            b = new Triangle(Double.parseDouble(txtSidea.getText()), Double.parseDouble(txtSideb.getText()), Double.parseDouble(txtSidec.getText()));
            a = new Box(Double.parseDouble(txtSidea.getText()), Double.parseDouble(txtSideb.getText()), Double.parseDouble(txtSidec.getText()));
            if (object  == 0) {
            txtOutput.setText("this is the volume " + a.getVolume());
            }
            else if (object == 2) {
                System.exit(0);
            }

        }

Answer 1

在按钮的操作监听器中，您应该检查组合框中选定的项目，而不是使用初始化期间设置的索引 (final int object = objectList.getSelectedIndex())当组合选择改变时不会改变。该变量甚至被标记为final。

例如，您可以执行类似的操作:

btnCalculate.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent arg0) {
       int selectedIndex = objectList.getSelectedIndex();
       if (selectedIndex == 0) {
           ...
       } else if selectedIndex == 2) {
          ...       
       }
    }
}