JFrame 动作侦听器在相同/链接的 JPanel 动作侦听器之前激活

Question

我是编程新手，正在尝试挥杆。我有一个用作默认菜单的 JFrame，还有一个出现在其中的 JPanel 来处理登录。成功登录后，JPanel 应该将登录信息发送到 JFrame，以便它知道当前登录的用户。

问题是，在 JButton 被单击时，在 JPanel 有机会检查凭据之前激活发送部分（其代码是 JFrame）。他们都使用相同的 actionlistener，所以我不知道如何控制顺序。

public class GUIFrame extends JFrame {

    private DetailsPanel detailsPanel;

    private String curUsername;

    public GUIFrame(String title){

        super(title);

        detailsPanel = new DetailsPanel();

        setLayout(new BorderLayout());

        Container c = getContentPane();

        c.add(detailsPanel, BorderLayout.EAST);

        detailsPanel.addActionListener(new ActionListener() {

            @Override

            public void actionPerformed(ActionEvent e) {

                if (!(detailsPanel.getCurUsername() == "")){

                    randomToBeImplementedFunctionThatWillLogIn();

                //TODO: 

                // The check here happens BEFORE the detailsPanel processes everything

                // so the first time they create an account it won't log them in

                // and every subsequent time the PREVIOUS login creds will be used. 

            }

        }

    });

public class DetailsPanel extends JPanel {

    private HashMap<String, String> logInMap = new HashMap<String, String>();

    private String curUsername = "";//the current logged in username

    public String getCurUsername(){

        return curUsername;

    }

    JTextField nameField;

    JTextField passField;

    public DetailsPanel(){

        nameField = new JTextField(0);

        passField = new JTextField(0);

         

    }

  

成功登录后，DetailsPanel 应该将信息发送到 GUIFrame，然后 GUIFrame 登录。

相反，当发生 actionlistener 时，GUIFrame 会在 DetailsPanel 开始检查凭据并将其发送到 GUIFrame 之前尝试登录。

有没有办法让 DetailsPanel.addActionListener() 在 logIn.addActionListener() 之后出现？

Answer 1

通常不能保证事件的顺序。从观察上看，它们倾向于按 FILO（先进后出）顺序触发。更好的解决方案是将流程解耦，这样任何感兴趣的各方都不会依赖按钮操作，而是依赖组件告诉他们验证何时发生。一个“简单”的解决方案是使用现有的 API 功能public class DetailsPanel extends JPanel {&nbsp; &nbsp; private HashMap<String, String> logInMap = new HashMap<String, String>();&nbsp; &nbsp; private String curUsername = "";//the current logged in username&nbsp; &nbsp; public String getCurUsername() {&nbsp; &nbsp; &nbsp; &nbsp; return curUsername;&nbsp; &nbsp; }&nbsp; &nbsp; JTextField nameField;&nbsp; &nbsp; JTextField passField;&nbsp; &nbsp; JButton logIn;&nbsp; &nbsp; public DetailsPanel() {&nbsp; &nbsp; &nbsp; &nbsp; nameField = new JTextField(0);&nbsp; &nbsp; &nbsp; &nbsp; passField = new JTextField(0);&nbsp; &nbsp; &nbsp; &nbsp; logIn.addActionListener((e) -> {//login attempted&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (logInMap.containsKey(nameField.getText())) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (passField.getText().equals(logInMap.get(nameField.getText()))) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; //logged in&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; curUsername = nameField.getText();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; fireActionPerformed();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } else {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; //wrong password, logged out&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; curUsername = "";&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } else {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; logInMap.put(nameField.getText(), passField.getText());&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; curUsername = nameField.getText();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; //create new account&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; });&nbsp; &nbsp; &nbsp; &nbsp; GridBagConstraints gCons = new GridBagConstraints();&nbsp; &nbsp; &nbsp; &nbsp; gCons.gridy = 0;&nbsp; &nbsp; &nbsp; &nbsp; gCons.gridx = 0;&nbsp; &nbsp; &nbsp; &nbsp; add(nameField, gCons);&nbsp; &nbsp; &nbsp; &nbsp; gCons.gridy = 1;&nbsp; &nbsp; &nbsp; &nbsp; add(passField, gCons);&nbsp; &nbsp; }&nbsp; &nbsp; public void addActionListener(ActionListener al) {&nbsp; &nbsp; &nbsp; &nbsp; listenerList.add(ActionListener.class, al);&nbsp; &nbsp; }&nbsp; &nbsp; protected void fireActionPerformed() {&nbsp; &nbsp; &nbsp; &nbsp; ActionListener[] listeners = listenerList.getListeners(ActionListener.class);&nbsp; &nbsp; &nbsp; &nbsp; if (listeners.length == 0) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return;&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; ActionEvent evt = new ActionEvent(this, ActionEvent.ACTION_PERFORMED, "validated");&nbsp; &nbsp; &nbsp; &nbsp; for (ActionListener listener : listeners) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; listener.actionPerformed(evt);&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }}所以，基本上，或者这样做，是将“已注册”存储ActionListener在 available 中listenerList。这是 Swing 提供的可用于所有 Swing 组件的 API。单击按钮并验证身份后，将通过该fireActionPerformed方法通知所有注册方。一个更完整的解决方案可能会涉及您自己的事件侦听interface器，它可以包括validationSuccess并且validationUnsuccessful可以将用户凭据作为事件对象的一部分传回