如何在 JFrame 中使用 KeyListener? [英] How to use KeyListener with JFrame?

问题描述

因此，我尝试使用 KeyEvent (KeyListener) 使矩形移动，但每当我尝试按下键时，矩形都不会移动.

So, I was trying to make a rectangle move with a KeyEvent (KeyListener) and whenever I try to hit the key, the rectangle doesn't move.

矩形已绘制，但每当我按下 left 和 right 键时，什么也没有发生.我有两个类，一个是带有 keyEvents 和框架的主类，另一个是绘制矩形并保存移动矩形的函数.

The rectangle is drawn, but whenever I hit the left and right keys, nothing happens. I have two classes, one is my main class with the keyEvents and the frame and the other, draws the rectangle and holds the function to move the rectangle.

这是我的代码:

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JFrame;


public class mainFrame extends JFrame implements KeyListener{

mainDraw Draw = new mainDraw();

public void keyPressed(KeyEvent e) {

    int key = e.getKeyCode();

    if(key == KeyEvent.VK_D){

        Draw.moveRight();
    }
}

public void keyReleased(KeyEvent e) {


}
public void keyTyped(KeyEvent e) {}

public mainFrame()
{
    addKeyListener(this);
    setFocusable(true);
    setFocusTraversalKeysEnabled(false);
}

public static void main(String[] args) {

    mainFrame M1 = new mainFrame();

    mainDraw Draw = new mainDraw();

    JFrame frame = new JFrame("Square Move Practice");


    //frame
    frame.setVisible(true);
    frame.setResizable(false);
    frame.setSize(600, 600);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().add(Draw);

}
}

现在是第二堂课:

import java.awt.Color;
import java.awt.Graphics;

import javax.swing.JComponent;

public class mainDraw extends JComponent{

public int x = 50;
public int y = 50;

public void paint(Graphics g){

    g.drawRect(x, y, 50, 50);
    g.fillRect(x, y, 50, 50);
    g.setColor(Color.BLACK);
}

public void moveRight()
{
    x = x + 5;
    y = y + 0;
    repaint();
}

}

请告诉我如何移动矩形.提前致谢！

Please tell me how I can move the rectangle. Thanks in advance!

推荐答案

矩形没有移动，因为您没有正确使用 JFrame.您必须将 frame 分配给 new mainFrame() 而不是忽略实例化的 mainFrame 对象.

The rectangle is not moving because you are not using JFrame correctly. You have to assign frame to new mainFrame() instead of ignoring the instantiated mainFrame object.

@MadProgrammer 指出还有其他几个问题.

There are several other issues as @MadProgrammer points out.

这是修复一些问题的代码:

Here is the code that fixes some of the issues:

import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.JFrame;


public class mainFrame extends JFrame implements KeyListener{
    private mainDraw draw;

    public void keyPressed(KeyEvent e) {
        System.out.println("keyPressed");
    }

    public void keyReleased(KeyEvent e) {
        if(e.getKeyCode()== KeyEvent.VK_RIGHT)
            draw.moveRight();
        else if(e.getKeyCode()== KeyEvent.VK_LEFT)
            draw.moveLeft();
        else if(e.getKeyCode()== KeyEvent.VK_DOWN)
            draw.moveDown();
        else if(e.getKeyCode()== KeyEvent.VK_UP)
            draw.moveUp();

    }
    public void keyTyped(KeyEvent e) {
        System.out.println("keyTyped");
    }

    public mainFrame(){
        this.draw=new mainDraw();
        addKeyListener(this);
        setFocusable(true);
        setFocusTraversalKeysEnabled(false);
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                mainFrame frame = new mainFrame();
                frame.setTitle("Square Move Practice");
                frame.setResizable(false);
                frame.setSize(600, 600);
                frame.setMinimumSize(new Dimension(600, 600));
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.getContentPane().add(frame.draw);
                frame.pack();
                frame.setVisible(true);
            }
        });
    }
}

mainDraw.java

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JComponent;

public class mainDraw extends JComponent {

    public int x = 50;
    public int y = 50;

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawRect(x, y, 50, 50);
        g.fillRect(x, y, 50, 50);
        g.setColor(Color.BLACK);
    }

    public void moveRight() {
        x = x + 5;
        repaint();
    }

    public void moveLeft() {
        x = x - 5;
        repaint();
    }

    public void moveDown() {
        y = y + 5;
        repaint();
    }

    public void moveUp() {
        y = y - 5;
        repaint();
    }
}

顺便说一句，使用 SwingUtilities 来放置 gui 更新代码，因为 Swing 对象不是线程安全的.

BTW, use SwingUtilities to put the gui update code because swing objects are not thread-safe.

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