【发布时间】：2021-10-28 17:35:59
【问题描述】：
在 GUI 中移动对象时，我看到很多使用计时器的视频和教程，但我尝试在没有它的情况下做一些事情，它似乎工作正常。 我不太明白什么时候需要一个计时器。 非常感谢任何帮助
包含两个移动物体但没有计时器的代码示例
import java.awt.Color;
import java.awt.Event;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.ImageIcon;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
public class Test2 extends JPanel{
int x=100,y=200,velX=5,velY=5;
int x2=300,y2=200;
Action upAction;
Action downAction;
Action leftAction;
Action rightAction;
Action wAction;
Action aAction;
Action sAction;
Action dAction;
JLabel label3 = new JLabel();
public Test2() {
this.setLayout(null);
this.setFocusable(true);
this.setBackground(Color.LIGHT_GRAY);
JLabel label1 = new JLabel("Press WASD to control Green Circle");
label1.setBounds(40, 30, 250, 20);
label1.setForeground(Color.GREEN);
this.add(label1);
JLabel label2 = new JLabel("Press Arrows to control Blue Circle");
label2.setBounds(250, 30, 250, 20);
label2.setForeground(Color.BLUE);
this.add(label2);
label3 = new JLabel("");
label3.setBounds(200, 200, 250, 20);
label3.setForeground(Color.RED);
this.add(label3);
upAction= new upAction();
downAction= new downAction();
leftAction = new leftAction();
rightAction = new rightAction();
wAction= new WAction();
aAction = new AAction();
sAction = new SAction();
dAction= new DAction();
this.getInputMap(WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke("UP"), "uplol");;
this.getActionMap().put("uplol", upAction);
this.getInputMap(WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke("DOWN"), "downlol");
this.getActionMap().put("downlol", downAction);
this.getInputMap(WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke("LEFT"), "leftlol");
this.getActionMap().put("leftlol", leftAction);
this.getInputMap(WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke("RIGHT"), "rightlol");
this.getActionMap().put("rightlol", rightAction);
this.getInputMap(WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke('w'), "moveup");;
this.getActionMap().put("moveup", wAction);
this.getInputMap(WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke('a'),"moveleft");
this.getActionMap().put("moveleft", aAction);
this.getInputMap(WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke('s'), "movedown");
this.getActionMap().put("movedown", sAction);
this.getInputMap(WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke('d'), "moveright");
this.getActionMap().put("moveright", dAction);
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.GREEN);
g.fillOval(x,y, 40, 40);
g.setColor(Color.BLUE);
g.fillOval(x2, y2, 40, 40);
}
public class upAction extends AbstractAction{
@Override
public void actionPerformed(ActionEvent e) {
y-=velY;
repaint();
checkCollision();
if(checkCollision()==true) {
label3.setText("OVER");
velY=0;
velX=0;
}
}
}
public class downAction extends AbstractAction{
@Override
public void actionPerformed(ActionEvent e) {
y+=velY;
repaint();
checkCollision();
if(checkCollision()==true) {
label3.setText("OVER");
velY=0;
velX=0;
}
}
}
public class rightAction extends AbstractAction{
@Override
public void actionPerformed(ActionEvent e) {
x+=velX;
repaint();
checkCollision();
if(checkCollision()==true) {
label3.setText("OVER");
velY=0;
velX=0;
}
}
}
public class leftAction extends AbstractAction{
@Override
public void actionPerformed(ActionEvent e) {
x-=velX;
repaint();
checkCollision();
if(checkCollision()==true) {
label3.setText("OVER");
velY=0;
velX=0;
}
}
}
public class WAction extends AbstractAction{
@Override
public void actionPerformed(ActionEvent e) {
y2-=velY;
repaint();
checkCollision();
if(checkCollision()==true) {
label3.setText("OVER");
velY=0;
velX=0;
}
}
}public class AAction extends AbstractAction{
@Override
public void actionPerformed(ActionEvent e) {
x2-=velX;
repaint();
checkCollision();
if(checkCollision()==true) {
label3.setText("OVER");
velY=0;
velX=0;
}
}
}public class DAction extends AbstractAction{
@Override
public void actionPerformed(ActionEvent e) {
x2+=velY;
repaint();
checkCollision();
if(checkCollision()==true) {
label3.setText("OVER");
velY=0;
velX=0;
}
}
}public class SAction extends AbstractAction{
@Override
public void actionPerformed(ActionEvent e) {
y2+=velY;
repaint();
checkCollision();
if(checkCollision()==true) {
label3.setText("OVER");
velY=0;
velX=0;
}
}
}
public boolean checkCollision() {
if((Math.pow(Math.abs(x2-x),2)+Math.pow(Math.abs(y2-y), 2))<=1600) {
System.out.println("night");
return true;
}
return false;
}
}
带有计时器的代码示例
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Label;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.Ellipse2D;
import java.util.Timer;
import javax.swing.*;
public class Move extends JPanel implements ActionListener{
javax.swing.Timer timer= new javax.swing.Timer(5, this);
int y=0,x=0,velY=2,velX=2;
@Override
public void paint(Graphics g) {
super.paint(g);
this.setBackground(Color.MAGENTA);
Graphics2D graphics2d = (Graphics2D)g;
graphics2d.setColor(Color.BLUE);
graphics2d.fill3DRect(100, 150, 100, 30, true);
graphics2d.setColor(Color.RED);
graphics2d.fillOval(200, 250, 28, 61);
graphics2d.setColor(Color.BLACK);
graphics2d.drawString("That boy is a monster", 80, 35);
//timer.start();
}
public Move() {
this.setLayout(null);
JLabel rotter = new JLabel("fool");
rotter.setBounds(140, 200, 53, 90);
this.add(rotter);
}
@Override
public void actionPerformed(ActionEvent e) {
if(x<0||x>560) {
velX=-velX;
}
if(y<0|y>360) {
velY=-velY;
}
x+=velX;
y+=velY;
repaint();
}
}
【问题讨论】：
-
一些示例代码可以改进这个问题。
-
1) 不要覆盖绘画。 Swing 中的自定义绘制是通过覆盖
paintComponent(...)来完成的 2) 不要使用空布局。 3) 所有 Swing 组件都应确定自己的首选尺寸。在进行自定义绘画时，您会覆盖getPreferredSize()。 4) 一种绘画方法仅用于绘画。不要在绘画方法中启动 Timer。 -
GUI 是事件驱动的。通常，用户使用鼠标或键盘生成事件，GUI 会做出反应。因此，只要用户按下一个键，您就可以轻松移动您的对象 - 无需计时器。 Timer 仅用于在没有用户交互的情况下以设定的时间间隔生成事件。然后，您可以在生成事件时做任何您想做的事情。通常这用于动画。因此，例如，您可以不断地为围绕框架移动的对象设置动画。有关完整示例，请参阅：stackoverflow.com/a/54028681/131872。
-
Timer 的另一个用途是允许您处理多个键。只会为最后按下的键生成 KeyEvent。如果您想在游戏中同时通过举起/向右进行对角线运动怎么办？在这种情况下，您需要在按下每个键时对其进行跟踪，然后使用 Timer 以在两个方向上对对象应用移动。查看Motion Using the Keyboard中的
KeyboardAnimation.java示例
标签： java user-interface timer