在java中处理两个按键

Question

我的代码有问题，因为我不知道当你同时按下 ARROW UP 和 ARROW LEFT 等时如何让图片对角移动。这是我的代码：

 public void keyPressed(KeyEvent ke) {
    switch (ke.getKeyCode()) {
    case KeyEvent.VK_RIGHT: {
        cordX += 5;
    }
        break;
    case KeyEvent.VK_LEFT: {
        cordX -= 5;
    }
        break;
    case KeyEvent.VK_DOWN: {
        cordY += 5;
    }
        break;
    case KeyEvent.VK_UP: {
        cordY -= 3;
    }
        break;
    }
    repaint();
}

我不知道这是否可行

case KeyEvent.VK_UP  &&  KeyEvent.VK_LEFT: {
        cordY += 5;
    }
        break;

Answer 1

如果您使用 Swing 组件，请使用 Key Bindings API，请参阅How to Use Key Bindings，它将解决很多问题...

无论如何，解决方案（基本上）是相同的，您需要做的是定义一系列标志，这些标志定义当前按下了哪些键，并定期更新受这些标志影响的变量的状态

private boolean down, up, left, right;
//...

public void keyPressed(KeyEvent ke) {
    switch (ke.getKeyCode()) {
        case KeyEvent.VK_RIGHT:
            right = true;
            break;
        case KeyEvent.VK_LEFT:
            left = true;
            break;
        case KeyEvent.VK_DOWN:
            down = true;
            break;
        case KeyEvent.VK_UP:
            up = true;
            break;
    }
    updateState();
}

public void keyReleased(KeyEvent ke) {
    switch (ke.getKeyCode()) {
        case KeyEvent.VK_RIGHT:
            right = false;
            break;
        case KeyEvent.VK_LEFT:
            left = false;
            break;
        case KeyEvent.VK_DOWN:
            down = false;
            break;
        case KeyEvent.VK_UP:
            up = false;
            break;
    }
    updateState();
}

protected void updateState() {
    if (right) {
        cordX += 5;
    } else if (left) {
        cordX -= 5;
    }
    if (down) {
        cordY += 5;
    } else if (up) {
        cordY -= 3;
    }
    repaint();
}

然后您可以使用javax.swing.Timer 安排定期回调，该回调可用于调用updateState（而不是从键事件处理程序中调用它）。

查看How to use Swing Timers了解更多详情...

Answer 2

您可以使用Timer。

public class MyClass extends KeyAdapter implements ActionListener {

    private Timer timer; //this timer will update your object's position
    private int vx = 0; //these values indicate your objects velocity
    private int vy = 0; //they are updated as your arrow keys are pressed

    public MyClass() {
        this.timer = new Timer(100 /*the delay*/, this/*the listener*/);
        //the delay indicated how frequently you want to update your position, i chose 100ms, you may chose a different number
    }

    @Override public void keyPressed(KeyEvent ke) {
        switch (ke.getKeyCode()) {
            case KeyEvent.VK_RIGHT:
                vx = 5;
            break;
            case KeyEvent.VK_LEFT:
                vx = -5;
            break;
            case KeyEvent.VK_DOWN:
                vy = 5;
            break;
            case KeyEvent.VK_UP:
                vy = -3;
            break;
        }
        this.timer.start(); //start your timer when a key is pressed (will do nothing if it's already running)
    }

    //obviously, you will need to stop your objects once the keys are released.
    @Override public void keyReleased(KeyEvent ke) {
        switch(ke.getKeyCode()) {
            case KeyEvent.VK_RIGHT:
                vx = 0;
            break;
            case KeyEvent.VK_LEFT:
                vx = 0;
            break;
            case KeyEvent.VK_DOWN:
                vy = 0;
            break;
            case KeyEvent.VK_UP:
                vy = 0;
            break;
        }
        if(vx == 0 && vy == 0) this.timer.stop(); //no need to run the timer if no key is down
    }

    //this will be called regularly by the timer
    @Override public void actionPerformed(ActionEvent ae) {
        cordX += vx; //you just update the positions
        cordY += vy; //according to your variables
        repaint(); //then repaint
    }
}

编辑：您可以对此进行优化以避免（例如）同时按下左右键时出现奇怪的行为。