java - 何时需要在 GUI 中移动对象的计时器？
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
带有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;
}
}
带定时器的代码示例
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();
}
}
解决方案
只要你只是
- 直接对一个事件做出反应
- 并且只更新一次显示
...没有计时器就可以做到这一点。
您可以/应该使用计时器的情况是
- 如果你有一个正在进行的动画
- 如果您不直接对 UI 事件做出反应，而是从另一个线程调用“更改”。
那为什么要使用定时器呢？
- Swing（您正在使用的）不是线程安全的，因此从 EDT（事件调度线程）以外的线程更改某些 UI 元素可能会给您的 UI 带来混乱和混乱（非常奇怪的行为）。
- 如果你有正在进行的动画——通常需要某种循环——并且在 EDT 内执行所有这些操作，那么 UI 将无法对任何输入做出反应，甚至无法正确更新自身。
所以你使用一个自动的计时器：
- 在自己的线程中运行，因此 UI 不会阻塞
- 并调用 EDT 更新 UI 以保持线程安全和干净