java - 如何使用按键绑定(bind)而不是按键监听器

Question

我正在使用KeyListener在我的代码(游戏或其他)中作为我的屏幕对象对用户按键输入使用react的方式。这是我的代码:

public class MyGame extends JFrame {

    static int up = KeyEvent.VK_UP;
    static int right = KeyEvent.VK_RIGHT;
    static int down = KeyEvent.VK_DOWN;
    static int left = KeyEvent.VK_LEFT;
    static int fire = KeyEvent.VK_Q;

    public MyGame() {

//      Do all the layout management and what not...
        JLabel obj1 = new JLabel();
        JLabel obj2 = new JLabel();
        obj1.addKeyListener(new MyKeyListener());
        obj2.addKeyListener(new MyKeyListener());
        add(obj1);
        add(obj2);
//      Do other GUI things...
    }

    static void move(int direction, Object source) {

        // do something
    }

    static void fire(Object source) {

        // do something
    }

    static void rebindKey(int newKey, String oldKey) {

//      Depends on your GUI implementation.
//      Detecting the new key by a KeyListener is the way to go this time.
        if (oldKey.equals("up"))
            up = newKey;
        if (oldKey.equals("down"))
            down = newKey;
//      ...
    }

    public static void main(String[] args) {

        new MyGame();
    }

    private static class MyKeyListener extends KeyAdapter {

        @Override
        public void keyPressed(KeyEvent e) {

            Object source = e.getSource();
            int action = e.getExtendedKeyCode();

/* Will not work if you want to allow rebinding keys since case variables must be constants.
            switch (action) {
                case up:
                    move(1, source);
                case right:
                    move(2, source);
                case down:
                    move(3, source);
                case left:
                    move(4, source);
                case fire:
                    fire(source);
                ...
            }
*/
            if (action == up)
                move(1, source);
            else if (action == right)
                move(2, source);
            else if (action == down)
                move(3, source);
            else if (action == left)
                move(4, source);
            else if (action == fire)
                fire(source);
        }
    }
}

我的响应能力有问题:

• 我需要点击该对象才能使其工作。
• 按下其中一个键时得到的响应不是我希望的工作方式 - 响应太快或响应太迟钝。

为什么会发生这种情况以及如何解决这个问题？

Answer 1

这个答案解释并演示了如何使用键绑定(bind)而不是键监听器来达到教育目的。事实并非如此

• 如何用 Java 编写游戏。
• 良好的代码编写应该是什么样的(例如可见性)。
• 实现按键绑定(bind)的最有效(性能或代码方面)的方法。

是

• 我将发布此内容作为对关键听众有困难的任何人的答案。

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回答；阅读Swing tutorial on key bindings .

I don't want to read manuals, tell me why I would want to use key bindings instead of the beautiful code I have already!

嗯，Swing 教程解释了这一点

• 按键绑定(bind)不需要您单击组件(以使其获得焦点):
  • 消除从用户角度来看的意外行为。
  • 如果您有 2 个对象，它们无法同时移动，因为在给定时间只有 1 个对象可以获得焦点(即使您将它们绑定(bind)到不同的键)。
• 按键绑定(bind)更容易维护和操作:
  • 禁用、重新绑定(bind)、重新分配用户操作变得更加容易。
  • 代码更容易阅读。

OK, you convinced me to try it out. How does it work?

tutorial 有一个关于它的很好的部分。键绑定(bind)涉及 2 个对象 InputMap 和 ActionMap。 InputMap 将用户输入映射到操作名称，ActionMap 将操作名称映射到Action。当用户按下某个键时，会在输入映射中搜索该键并找到 Action 名称，然后在 Action 映射中搜索该 Action 名称并执行该 Action 。

Looks cumbersome. Why not bind the user input to directly to the action and get rid of the action name? Then you need only one map and not two.

好问题!您会发现这是使键绑定(bind)更易于管理的事情之一(禁用、重新绑定(bind)等)。

I want you to give me a full working code of this.

否(Swing 教程有 working examples )。

You suck! I hate you!

以下是如何进行单键绑定(bind):

myComponent.getInputMap().put("userInput", "myAction");
myComponent.getActionMap().put("myAction", action);

请注意，有 3 个 InputMap 对不同的焦点状态使用react:

myComponent.getInputMap(JComponent.WHEN_FOCUSED);
myComponent.getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT);
myComponent.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);

• WHEN_FOCUSED 也是在未提供参数时使用的，在组件具有焦点时使用。这与关键监听器的情况类似。
• WHEN_ANCESTOR_OF_FOCUSED_COMPONENT 当焦点组件位于注册为接收操作的组件内部时使用。如果一艘宇宙飞船内有许多船员，并且您希望宇宙飞船在任何船员获得焦点时继续接收输入，请使用此选项。
• WHEN_IN_FOCUSED_WINDOW 在注册接收操作的组件位于焦点组件内部时使用。如果您在聚焦窗口中有许多坦克，并且希望所有坦克同时接收输入，请使用此选项。

假设要同时控制两个对象，问题中提供的代码将类似于以下内容:

public class MyGame extends JFrame {

    private static final int IFW = JComponent.WHEN_IN_FOCUSED_WINDOW;
    private static final String MOVE_UP = "move up";
    private static final String MOVE_DOWN = "move down";
    private static final String FIRE = "move fire";

    static JLabel obj1 = new JLabel();
    static JLabel obj2 = new JLabel();

    public MyGame() {

//      Do all the layout management and what not...

        obj1.getInputMap(IFW).put(KeyStroke.getKeyStroke("UP"), MOVE_UP);
        obj1.getInputMap(IFW).put(KeyStroke.getKeyStroke("DOWN"), MOVE_DOWN);
//      ...
        obj1.getInputMap(IFW).put(KeyStroke.getKeyStroke("control CONTROL"), FIRE);
        obj2.getInputMap(IFW).put(KeyStroke.getKeyStroke("W"), MOVE_UP);
        obj2.getInputMap(IFW).put(KeyStroke.getKeyStroke("S"), MOVE_DOWN);
//      ...
        obj2.getInputMap(IFW).put(KeyStroke.getKeyStroke("T"), FIRE);

        obj1.getActionMap().put(MOVE_UP, new MoveAction(1, 1));
        obj1.getActionMap().put(MOVE_DOWN, new MoveAction(2, 1));
//      ...
        obj1.getActionMap().put(FIRE, new FireAction(1));
        obj2.getActionMap().put(MOVE_UP, new MoveAction(1, 2));
        obj2.getActionMap().put(MOVE_DOWN, new MoveAction(2, 2));
//      ...
        obj2.getActionMap().put(FIRE, new FireAction(2));

//      In practice you would probably create your own objects instead of the JLabels.
//      Then you can create a convenience method obj.inputMapPut(String ks, String a)
//      equivalent to obj.getInputMap(IFW).put(KeyStroke.getKeyStroke(ks), a);
//      and something similar for the action map.

        add(obj1);
        add(obj2);
//      Do other GUI things...
    }

    static void rebindKey(KeyEvent ke, String oldKey) {

//      Depends on your GUI implementation.
//      Detecting the new key by a KeyListener is the way to go this time.
        obj1.getInputMap(IFW).remove(KeyStroke.getKeyStroke(oldKey));
//      Removing can also be done by assigning the action name "none".
        obj1.getInputMap(IFW).put(KeyStroke.getKeyStrokeForEvent(ke),
                 obj1.getInputMap(IFW).get(KeyStroke.getKeyStroke(oldKey)));
//      You can drop the remove action if you want a secondary key for the action.
    }

    public static void main(String[] args) {

        new MyGame();
    }

    private class MoveAction extends AbstractAction {

        int direction;
        int player;

        MoveAction(int direction, int player) {

            this.direction = direction;
            this.player = player;
        }

        @Override
        public void actionPerformed(ActionEvent e) {

            // Same as the move method in the question code.
            // Player can be detected by e.getSource() instead and call its own move method.
        }
    }

    private class FireAction extends AbstractAction {

        int player;

        FireAction(int player) {

            this.player = player;
        }

        @Override
        public void actionPerformed(ActionEvent e) {

            // Same as the fire method in the question code.
            // Player can be detected by e.getSource() instead, and call its own fire method.
            // If so then remove the constructor.
        }
    }
}

您可以看到，将输入映射与操作映射分开可以实现可重用的代码和更好的绑定(bind)控制。此外，如果您需要该功能，还可以直接控制Action。例如:

FireAction p1Fire = new FireAction(1);
p1Fire.setEnabled(false); // Disable the action (for both players in this case).

请参阅Action tutorial了解更多信息。

I see that you used 1 action, move, for 4 keys (directions) and 1 action, fire, for 1 key. Why not give each key its own action, or give all keys the same action and sort out what to do inside the action (like in the move case)?

好点。从技术上讲，您可以两者兼得，但您必须考虑什么是有意义的以及什么可以轻松管理和可重用代码。这里我假设所有方向的移动都是相似的，而射击是不同的，所以我选择了这种方法。

I see a lot of KeyStrokes used, what are those? Are they like a KeyEvent?

是的，它们有类似的功能，但更适合用在这里。查看他们的API获取信息以及如何创建它们。

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