如何使用 KeyListener 同时检测多个键？

Posted 2023-03-27

【中文标题】如何使用 KeyListener 同时检测多个键？

【英文标题】：How to detect multiple keys at the same time using KeyListener?

【发布时间】：2016-01-27 16:56:26

【问题描述】：

问题说明了一切！这是我的代码和我尝试使用嵌套的 if 语句，但最终失败了。我只想制作我的代码，以便当用户按住 shift 和 down 时，它会加载不同的图像：

package Michael;

import java.awt.Canvas;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;

public class MyCanvas extends Canvas implements KeyListener /* Creates the     MyScreen method 
                                                        which extends (inherits) from 
                                                        Canvas and implements (uses) 
                                                        KeyListener. */

int myX = 100; // Set the initial x coordinate.
int myY = 100; // Set the initial y coordinate.

BufferedImage down; // Loads the Image.

    try
    
        down = ImageIO.read(new File("Images/down.png")); /* Loads the image from 
                                                          'Images/down.png'.*/
    

    catch (IOException e)
    
        System.out.println("Cannot find image file."); /* If the file location is
                                                       non-existent, print on a new line
                                                       'Cannot find Image File'.*/
    
 

/* The exact same process is done for the next 9 images loaded, just with different,
appropriate, variable names and locations. */

BufferedImage downrun;

    try
    
        downrun = ImageIO.read(new File("Images/downrun.png"));
    

    catch (IOException e)
    
        System.out.println("Cannot find image file.");
    


BufferedImage left;

    try
    
        left = ImageIO.read(new File("Images/left.png"));
    

    catch (IOException e)
    
        System.out.println("Cannot find image file.");
    


BufferedImage right;

    try
    
        right = ImageIO.read(new File("Images/right.png"));
    

    catch (IOException e)
    
        System.out.println("Cannot find image file.");
    


BufferedImage runleft;

    try
    
        runleft = ImageIO.read(new File("Images/runleft.png"));
    

    catch (IOException e)
    
        System.out.println("Cannot find image file.");
    


BufferedImage runright;

    try
    
        runright = ImageIO.read(new File("Images/runright.png"));
    

    catch (IOException e)
    
        System.out.println("Cannot find image file.");
    


BufferedImage swoosh;

    try
    
        swoosh = ImageIO.read(new File("Images/swoosh.png"));
    

    catch (IOException e)
    
        System.out.println("Cannot find image file.");
    


BufferedImage swordraise;

    try
    
        swordraise = ImageIO.read(new File("Images/swordraise.png"));
    

    catch (IOException e)
    
        System.out.println("Cannot find image file.");
    


BufferedImage up;

    try
    
        up = ImageIO.read(new File("Images/up.png"));
    

    catch (IOException e)
    
        System.out.println("Cannot find image file.");
    


BufferedImage uprun;

    try
    
        uprun = ImageIO.read(new File("Images/uprun.png"));
    

    catch (IOException e)
    
        System.out.println("Cannot find image file.");
    


public MyCanvas() // The MyCanvas constructor.

    this.setSize(600, 400); // Makes the size of the canvas 600 x 400.
    this.addKeyListener(this); // Adds KeyListener.
    this.setBackground(Color.WHITE); // Make the background white.
    this.setFocusable(true); // Make the window automatically focused.


String image; // Creates the image variable as a string.

public void paint(Graphics g) // The paint method using Graphics.

    if (image == "down")
    
        g.drawImage(down, myX, myY, 55, 55, null);
    

    else if (image == "up")
    
        g.drawImage(up, myX, myY, 55, 55, null);
    

    else if (image == "left")
    
        g.drawImage(left, myX, myY, 55, 55, null);
    

    else if (image == "right")
    
        g.drawImage(right, myX, myY, 55, 55, null);
    

    else if (image == "swoosh")
    
        g.drawImage(swoosh, myX, myY, 55, 55, null);
    

    else if (image == "swordraise")
    
        g.drawImage(swordraise, myX, myY, 55, 55, null);
    

    else if (image == "downrun")
    
        g.drawImage(downrun, myX, myY, 55, 55, null);
    

    else
    
        g.drawImage(right, myX, myY, 55, 55, null);
    



@Override
public void keyPressed(KeyEvent e) // When the key is pressed:
   
    if (e.getKeyCode() == KeyEvent.VK_DOWN) // If the down arrow is pressed:
    
        image = "down";
        myY += 10; // Increase the y coordinate by 10 (moves down).
    

    else if (e.getKeyCode() == KeyEvent.VK_UP) // If the up arrow is pressed:
    
        image ="up";
        myY -= 10; // Decrease the y coordinate by 10 (moves up).
    

    else if (e.getKeyCode() == KeyEvent.VK_LEFT) // If the left arrow is pressed:
    
        image = "left";
        myX -= 10; // Decrease the x coordinate by 10 (moves left).
    

    else if (e.getKeyCode() == KeyEvent.VK_RIGHT) // If the right arrow is pressed:
    
        image = "right";
        myX += 10; // Increase the x coordinate by 10 (moves right)
    

    else if (e.getKeyCode() == KeyEvent.VK_1) // If the 1 button is pressed:
    
        image = "swordraise";
    

    else if (e.getKeyCode() == KeyEvent.VK_SHIFT)
    
        if (e.getKeyCode() == KeyEvent.VK_DOWN)
        
            image = "downrun";
            myY += 50;
        
    

    repaint(); // Refresh the Images.


@Override
public void keyTyped(KeyEvent e) // When the key is typed:

    // TODO Auto-generated method stub


@Override
public void keyReleased(KeyEvent e) // When the key is released:

    if (e.getKeyCode() == KeyEvent.VK_1) // If the 1 button is released:
    
        image = "swoosh";
    

    repaint();

非常感谢！

【问题讨论】：

对于example。您的代码中几乎没有表明需要Canvas，这无法通过使用JPanel 来解决，它提供了使用键绑定API 的能力，它克服了KeyListener 的一些烦人的限制

【参考方案1】：

这个答案为 Michael 提供了一种稍微不同的方法，将所有按键的键码存储在 ArrayList 数据结构中，而不是布尔数组。

ArrayList<int> keys=new ArrayList();
//This ArrayList will hold all the key codes of currently pressed keys.

@Override
public void keyPressed(KeyEvent k)
    if(!keys.contains(k.getKeyCode()))
        keys.add(k.getKeyCode());
    


@Override
public void keyReleased(KeyEvent k)
    if(keys.contains(k.getKeyCode()))
        keys.remove(keys.indexOf(k.getKeyCode()));
    

要测试当前是否按下了 shift 键，请运行此代码，因为 shift 的键代码是 16：

    keys.contains(16);

【参考方案2】：

您可以创建一个布尔数组，表示一个键是一个还是关闭现在。

boolean[] keys = new boolean[500];//whatever the highest keycode is
//....
public void keyPressed(KeyEvent e)
    keys[e.getKeyCode] = true;


public void keyReleased(KeyEvent e)
    keys[e.getKeyCode] = false;

然后，在您的更新（或者在这种情况下，您的 paint）方法中，您可以像这样使用您的数组：

public void update()
    if (keys[KeyEvent.VK_SHIFT] && keys[KeyEvent.VK_DOWN])
        //user is holding down both shift and down arrow key
    

【讨论】：

KeyCode.VK_Whatever@McGovno 的最高值

//用户同时按住两者..什么？ :)

那么我的最高键码是多少？我的 keycode 没有数字，所以我有点困惑...

KeyEvent.VK_SHIFT 是一个数字；一个int 具体来说。因此，为确保您在访问keys[e.getKeyCode] 时永远不会越界，请确保将其设置得足够大以容纳最大的KeyEvent.VK 值@McGovno

@Michael Code 有点工作，除了当我按住 shift 并点击 down 键时，没有任何反应，但如果我按住 down 键并点击 shift，它会冲刺。我希望它是相反的方式，但我似乎无法弄清楚如何做到这一点。