Question

我一直试图找出如何使用箭头键移动矩形，但似乎有问题我使用f来检测所有关键输入我不知道如何使用KeyBinding因此我不希望有解决方案我打算在掌握KeyListener之后立即学习它。请给我一些如何解决它的建议。

KeyListener

Answer 1

使用KeyListener上的键绑定API，它解决了KeyListener遭受的焦点相关问题。 How to Use Key Bindings
不要打破油漆链。如果您覆盖其中一种paint方法，则必须将其称为super实施方式。
避免覆盖paint，它通常在绘画过程中处于高位，并且由于绘画的工作方式，在绘制子组件时不会总是被调用，这可能会导致一些有趣的问题。公约建议改为使用paintComponent。有关详细信息，请参阅Painting in AWT and Swing和Performing Custom Painting
最后尝试拨打JFrame#setVisible，在您建立用户界面后，您会发现它会导致较少的问题

作为一个例子......

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Expo extends JPanel {

    int x = 0;
    int y = 0;

    public Expo() {
        bindKeyStrokeTo(WHEN_IN_FOCUSED_WINDOW, "down", KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0), new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {
                y += 2;
                if (y + 100 > getHeight()) {
                    y = getHeight() - 100;
                }
                repaint();
            }
        });
        bindKeyStrokeTo(WHEN_IN_FOCUSED_WINDOW, "up", KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0), new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {
                y -= 2;
                if (y < 0) {
                    y = 0;
                }
                repaint();
            }
        });
    }

    public void bindKeyStrokeTo(int condition, String name, KeyStroke keyStroke, Action action) {
        InputMap im = getInputMap(condition);
        ActionMap am = getActionMap();

        im.put(keyStroke, name);
        am.put(name, action);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(Color.BLUE);
        g.drawRect(x, y, 100, 100);
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(500, 500);
    }

    public static void main(String[] args) throws InterruptedException {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new Expo());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

}

这一切都很酷，但是现在，当你按住键时，矩形会移动，暂停，然后开始稳定地移动！？

这实际上很正常。相反，你可以做的是建立一个更新循环＆＃34;它会持续监视一组标志的状态，决定在设置这些标志时要做什么并更新UI。

所以，这样做，是设置一个Swing Timer，每40毫秒滴答一次，检查当前＆＃34;垂直键状态＆＃34;的状态，更新y位置相应地安排一个repaint，这样可以让我们更顺畅地运动，因为我们不依赖于重复击键。

这也证明了键绑定API的强大功能，因为它建立了一个Action来处理向上和向下移动以及相关的键释放......整洁

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Expo extends JPanel {

    int x = 0;
    int y = 0;

    public enum VerticalKey {

        UP, DOWN, NONE;
    }

    public enum HorizontalKey {

        LEFT, RIGHT, NONE;
    }

    private VerticalKey verticalKeyState = VerticalKey.NONE;
    private HorizontalKey horizontalKeyState = HorizontalKey.NONE;

    public Expo() {
        bindKeyStrokeTo(WHEN_IN_FOCUSED_WINDOW, "pressed.down", KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0), new VerticalAction(VerticalKey.DOWN));
        bindKeyStrokeTo(WHEN_IN_FOCUSED_WINDOW, "released.down", KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0, true), new VerticalAction(VerticalKey.NONE));
        bindKeyStrokeTo(WHEN_IN_FOCUSED_WINDOW, "pressed.up", KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0), new VerticalAction(VerticalKey.UP));
        bindKeyStrokeTo(WHEN_IN_FOCUSED_WINDOW, "released.up", KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0, true), new VerticalAction(VerticalKey.NONE));

        Timer timer = new Timer(40, new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                switch (verticalKeyState) {
                    case UP:
                        y -= 2;
                        break;
                    case DOWN:
                        y += 2;
                        break;
                }
                if (y + 100 > getHeight()) {
                    y = getHeight() - 100;
                } else if (y < 0) {
                    y = 0;
                }

                repaint();
            }
        });
        timer.start();
    }

    public void bindKeyStrokeTo(int condition, String name, KeyStroke keyStroke, Action action) {
        InputMap im = getInputMap(condition);
        ActionMap am = getActionMap();

        im.put(keyStroke, name);
        am.put(name, action);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(Color.BLUE);
        g.drawRect(x, y, 100, 100);
    }

    public void setVerticalKeyState(VerticalKey verticalKeyState) {
        this.verticalKeyState = verticalKeyState;
        System.out.println(verticalKeyState);
    }

    public void setHorizontalKeyState(HorizontalKey horizontalKeyState) {
        this.horizontalKeyState = horizontalKeyState;
    }

    public class VerticalAction extends AbstractAction {

        private VerticalKey verticalKey;

        public VerticalAction(VerticalKey verticalKeys) {
            this.verticalKey = verticalKeys;
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            setVerticalKeyState(verticalKey);
        }

    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(500, 500);
    }

    public static void main(String[] args) throws InterruptedException {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new Expo());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

}

Answer 2

只需更改这两段代码：

@Override
public void keyPressed(KeyEvent e) {

    if(e.getKeyCode() == KeyEvent.VK_DOWN){
        System.out.println("Key Pressed" + e.getKeyCode());
        y = y + 2;

        repaint();//add this line to update the UI
    }
}

和

public void paint(Graphics g){
    super.paint(g);//you should always call the super-method first

    g.setColor(Color.BLUE);
    g.drawRect(x ,y,100,100);
}

这可以解决问题。虽然我建议覆盖paintComponent而不是paint（请参阅有关＆＃34; The Paint Methods＆＃34;在本文中的部分：Painting in AWT and Swing）。基本上我改变了以下内容：
在keyPressed这一行：repaint();将在广场移动后更新用户界面。实际上广场在移动之前已被移动，但是在更新UI之前，更改不会显示。在paint这一行：super.paint(g);使面板首先执行默认绘制，其中包括清除整个面板。我已经删除了repaint();电话，因为它完全没用。

注意：如果您使用paintComponent代替paint，则必须将第一个来电从super.paint(g)更改为super.paintComponent(g)以避免堆叠溢出。

如何使用java中的键移动矩形

2 个答案: