Java 如何使用箭头键在屏幕上移动图形？
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How do I move a graphic across the screen with arrow keys?
提问by Bfrank
I'm trying to create the beginning of a simple game. The first thing I am trying to do is import a graphic into my code and move it across the screen. I was able to draw a ball on the screen and move it around but when I import a graphic from a file I am unable to move it around. What am I missing or doing wrong?
我正在尝试创建一个简单游戏的开始。我尝试做的第一件事是将图形导入到我的代码中并在屏幕上移动它。我能够在屏幕上绘制一个球并移动它，但是当我从文件导入图形时，我无法移动它。我错过了什么或做错了什么？
import javax.swing.*;
import java.awt.Graphics;
import java.awt.*;
import java.awt.event.*;
import javax.swing.ImageIcon;
import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyListener;
import javax.swing.JPanel;
import javax.swing.Timer;
public class Game extends JPanel implements ActionListener, KeyListener {
Timer t = new Timer(5, this);
double x = 0, y = 0, velX = 0, velY = 0;
private ImageIcon image;
public Game(){
setBackground(Color.WHITE);
t.start();
addKeyListener(this);
this.setFocusable(true);
setFocusTraversalKeysEnabled(false);
image = new ImageIcon ("ship.gif");
}
public void paintComponent(Graphics g){
super.paintComponent(g);
ImageIcon i = new ImageIcon("C:\Users\Bryan\Pictures\ship.gif");
i.paintIcon(this, g, 0, 0);
}
public void actionPerformed(ActionEvent e){
repaint();
x += velX;
y += velY;
if(x<0){
velX = 0;
x = 0;
}
if(x>750){
velX = 0;
x = 750;
}
if(y<0);{
velY = 0;
y = 0;
}
if(y>550){
velY = 0;
y = 550;
}
}
public void up(){
velY = -1.5;
velX = 0;
}
public void down(){
velY = 1.5;
velX = 0;
}
public void left(){
velX = -1.5;
velY = 0;
}
public void right(){
velX = 1.5;
velY = 0;
}
public void keyPressed(KeyEvent e){
int code = e.getKeyCode();
if (code == KeyEvent.VK_UP){
up();
}
if (code == KeyEvent.VK_DOWN){
down();
}
if (code == KeyEvent.VK_LEFT){
left();
}
if (code == KeyEvent.VK_RIGHT){
right();
}
}
public void keyTyped(KeyEvent e){}
public void keyReleased(KeyEvent e){
// velX = 0;
// velY = 0;
int code = e.getKeyCode();
if (code == KeyEvent.VK_UP){
velY = 0;
}
if (code == KeyEvent.VK_DOWN){
velY = 0;
}
if (code == KeyEvent.VK_LEFT){
velX = 0;
}
if (code == KeyEvent.VK_RIGHT){
velX = 0;
}
}
}
My driver is in another class as follows:
我的司机在另一个班级如下：
import java.awt.Color;
import javax.swing.JFrame;
public class GameDriver {
public static void main(String[] args) {
JFrame f = new JFrame();
Game g = new Game();
f.add(g);
f.setVisible(true);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setSize(800,600);
}
}
采纳答案by Hovercraft Full Of Eels
Two big problems here:
这里有两个大问题：
public void paintComponent(Graphics g){
super.paintComponent(g);
ImageIcon i = new ImageIcon("C:\Users\Bryan\Pictures\ship.gif");
i.paintIcon(this, g, 0, 0);
}
- You're reading from a file from within
paintComponent(...). Neverdo this as this will slow your drawing unnecessarily. Read the image once, perhaps in a constructor, and then use the stored image variable in drawing. The paintComponent method should be for painting only, and it should be lean, mean and fast. - You're drawing at 0, 0 always. If you want to move something, draw at a variable position, and then change the values held by the variable and repaint.
- 您正在从
paintComponent(...). 切勿这样做，因为这会不必要地减慢您的绘图速度。读取图像一次，可能在构造函数中，然后在绘图中使用存储的图像变量。该方法的paintComponent应该是绘画只是，它应该是瘦肉，平均和快速。 - 你总是在 0, 0 处绘制。如果要移动某些东西，请在变量位置绘制，然后更改变量保存的值并重新绘制。
Also: You should use Key Bindings to accept key strokes in a Swing application as this will help solve focus issues.
另外：您应该使用键绑定来接受 Swing 应用程序中的击键，因为这将有助于解决焦点问题。
For example, please have a look at my code in this answer.
例如，请看看我在这个答案中的代码。
