Noo*_*ick 3 java swing actionlistener itemlistener
我正在为班级创建一个程序，其中您有一个 JComboBox，当选择一个选项时，它会弹出一个包含不同选项的窗口。我有一个选项可以弹出一个新窗口，上面有两个按钮。
\n\n首先，我不确定是否应该使用 ItemListener 或 ActionListener 作为 JComboBox 选项。现在我有一个 ItemListener，我认为它仅适用于“矩阵”选项，但它适用于这两个选项，我不明白为什么。我将发布所有代码以防万一，但我将在指定问题的上方和下方添加星星。
\n\n感谢您的帮助或为我指明正确的方向！
\n\npublic class MultiForm extends JFrame{\n\n\n private JComboBox menu;\n private JButton bluePill;\n private JButton redPill;\n private JLabel matrix;\n private int matrixSelection;\n private static String[] fileName = {"", "The Matrix", "Another Option"};\n\npublic MultiForm() {\n super("Multi Form Program"); \n setLayout(new FlowLayout());\n menu = new JComboBox(fileName);\n add(menu);\n\n ************************************************************************* \n TheHandler handler = new TheHandler();\n menu.addItemListener(handler); \n}\n\nprivate class TheHandler implements ItemListener{\n public void itemStateChanged(ItemEvent event) {\n\n if(event.getStateChange() == ItemEvent.SELECTED) {\n menu.setSelectedItem("The Matrix");\n menu.getSelectedIndex();\n*************************************************************************\n //Create a new window when "The Matrix" is clicked in the JCB\n JFrame newFrame = new JFrame();\n JPanel panel = new JPanel();\n\n newFrame.setLayout(new FlowLayout());\n newFrame.setSize(500, 300);\n newFrame.setDefaultCloseOperation(newFrame.EXIT_ON_CLOSE);\n add(panel, BorderLayout.CENTER);\n\n matrix = new JLabel("<html>After this, there is no turning back. "\n + "<br>You take the blue pill\xe2\x80\x94the story ends, you wake up "\n + "<br>in your bed and believe whatever you want to believe."\n + "<br>You take the red pill\xe2\x80\x94you stay in Wonderland, and I show"\n + "<br>you how deep the rabbit hole goes. Remember: all I\'m "\n + "<br>offering is the truth. Nothing more.</html>");\n newFrame.add(matrix, BorderLayout.NORTH);\n\n Icon bp = new ImageIcon(getClass().getResource("Blue Pill.png"));\n bluePill = new JButton("Blue Pill", bp);\n newFrame.add(panel.add(bluePill)); \n\n Icon rp = new ImageIcon(getClass().getResource("Red Pill.png"));\n redPill = new JButton("Red Pill", rp);\n newFrame.add(panel.add(redPill)); \n\n\n newFrame.setVisible(true);\n } \n }\n}\n\npublic static void main(String[] args) {\n MultiForm go = new MultiForm();\n go.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);\n go.setSize(400, 200);\n go.setVisible(true);\n}\n}\nItemListener并ActionListener会告知组合框何时发生变化。然后，您需要确定发生了什么变化并采取适当的措施
例如...
private class TheHandler implements ItemListener{
public void itemStateChanged(ItemEvent event) {
if(event.getStateChange() == ItemEvent.SELECTED) {
Object source = event.getSource();
if (source instanceof JComboBox) {
JComboBox cb = (JComboBox)source;
Object selectedItem = cb.getSelectedItem();
if ("The Matrix".equals(selectedItem)) {
// Do the matrix
} else if ("Another Option".equals(selectedItem)) {
// Do another option
}
}
}
}
}
这只是检查是什么selectedItem，并根据选择的内容采取适当的操作。您也可以使用selectedIndex相反的方法，它将返回一个int代表所选项目的值，但哪个对您来说更容易。
查看如何使用组合框了解更多详细信息
如果您想知道的是何时选择一个项目，您可能会发现更ActionListener简单，因为您不需要检查状态 ( SELECTED/ UNSELECTED)，因为它仅在选定状态更改时触发