Question

我试图使用KeyBinding移动矩形，但我想我无法正确实现它。我是java的初学者，我无法在这个程序中找到错误所以请帮帮我。

Thnx提前!!

import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.AbstractAction;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.SwingUtilities;
import javax.swing.Timer;

class Move {

    public static void main(String args[]) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                abc();
            }
        });
    }

    private static void abc() {
        JFrame frame = new JFrame("moving object");
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(1300, 600);
        frame.add(new P1());
    }
}

class P1 extends JPanel {

    int a, b;
    int x, y;
    Timer t = new Timer(10, new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {//the coordinates of this rectangle 
            a += x;                                 //are mordified in every 10 millisec 
            b += y;                                 //x and y changes the direction of the moving
            repaint();                              //rect. 
        }
    });

    P1() {
        this.getInputMap().put(KeyStroke.getKeyStroke("VK_UP"), "doNothing1");
        this.getActionMap().put("doNothing1", new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {
                x = 0;
                y = -1;
            }
        });
        this.getInputMap().put(KeyStroke.getKeyStroke("VK_LEFT"), "doNothing2");
        this.getActionMap().put("doNothing2", new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {
                x = -1;
                y = 0;
            }
        });
        this.getInputMap().put(KeyStroke.getKeyStroke("VK_DOWN"), "doNothing3");
        this.getActionMap().put("doNothing3", new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {
                x = 0;
                y = 1;
            }
        });
        this.getInputMap().put(KeyStroke.getKeyStroke("VK_RIGHT"), "doNothing4");
        this.getActionMap().put("doNothing4", new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {
                x = -1;
                y = 0;
            }
        });
        t.start();
        setFocusable(true);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.fillRect(a, b, 10, 10);
    }
}

Answer 1

您使用的是错误的InputMap，这是导致问题的一个主要原因。当你没有指定condtion时获得的默认InputMap使用WHEN_FOCUSED条件，并且由于JPanels默认情况下不允许焦点（并且实际上不应该强制获得焦点），这将不起作用。您将希望使用具有WHEN_IN_FOCUSED_WINDOW条件的那个。为此，您必须明确指定此项。即：

InputMap inputMap = getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW); // note condition
inputMap.put(KeyStroke.getKeyStroke("VK_UP"), "doNothing1");
// ....

即使绑定组件没有焦点，只要它保存在具有焦点的顶级窗口中，这也会起作用。

无法实现KeyBinding

1 个答案: