actionListener on jcheckbox

Question

我正在尝试向JCheckBox添加一个匿名actionListener，但是在访问我想要用来更新值的对象时遇到了一些困难。我一直收到关于非final的错误，然后当我将它们更改为final时，它会抱怨其他事情。

我尝试做的事情如下(我删除了一些gui代码以使其更容易阅读)：

for (FunctionDataObject fdo : wdo.getFunctionDataList())
{
    JLabel inputTypesLabel = new JLabel("Input Types: ");
    inputsBox.add(inputTypesLabel);
    for (int i = 0; i < fdo.getNumberOfInputs(); i++)
    {
        JLabel inputLabel = new JLabel(fdo.getInputNames().get(i));
        JComboBox inputTypeComboBox = new JComboBox(getTypes());
        inputTypeComboBox.addActionListener(new ActionListener() {
             public void actionPerformed(ActionEvent e) 
             {
                 fdo.getInputTypes().set(i, (String) inputTypeComboBox.getSelectedItem());
             }
        });
     }
}    

Answer 1

您不能访问匿名类中的非final变量。你可以稍微修改一下你的代码来绕过这个限制(我已经完成了fdo和inputTypeComboBox的最终版本，我也完成了i的最终版本)：

    for (final FunctionDataObject fdo : wdo.getFunctionDataList()) {
        JLabel inputTypesLabel = new JLabel("Input Types: ");
        inputsBox.add(inputTypesLabel);
        for (int i = 0; i < fdo.getNumberOfInputs(); i++) {
            final int final_i = i;
            JLabel inputLabel = new JLabel(fdo.getInputNames().get(i));
            final JComboBox inputTypeComboBox = new JComboBox(getTypes());
            inputTypeComboBox.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    fdo.getInputTypes().set(final_i, (String) inputTypeComboBox.getSelectedItem());
                }
            });
        }
    }

Answer 2

从更新您的代码

 inputTypeComboBox.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) 
         {
             fdo.getInputTypes().set(i, (String) inputTypeComboBox.getSelectedItem());
         }
    });

至

final counter = i;
final JComboBox inputTypeComboBox = new JComboBox(getTypes());
final FunctionDataObject finalFDO = fdo;
inputTypeComboBox.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) 
         {
             finalFDO.getInputTypes().set(counter, (String) inputTypeComboBox.getSelectedItem());
         }
    });

This链接解释了为什么只能访问内部类中的最终变量

Answer 3

这将会起作用：

    for (final FunctionDataObject fdo : wdo.getFunctionDataList()) {
        JLabel inputTypesLabel = new JLabel("Input Types: ");
        inputsBox.add(inputTypesLabel);
        for (int i = 0; i < fdo.getNumberOfInputs(); i++) {
            JLabel inputLabel = new JLabel(fdo.getInputNames().get(i));
            final JComboBox inputTypeComboBox = new JComboBox(getTypes());
            final int index = i;
            inputTypeComboBox.addActionListener(new ActionListener() {
                 public void actionPerformed(ActionEvent e) {
                     fdo.getInputTypes().set(index, (String) inputTypeComboBox.getSelectedItem());
                 }
            });
         }
    }