Canvas对象未显示，但位置在Java Applet中正确更新
我的基本弹跳球Applet应该根据loc变量中的值移动一个球，但没有任何显示。 打印出来的地方显示数字/数学背后移动它并且跳出边界确实正常工作，但没有任何显示。 在线查看示例我不明白为什么我的绘图/绘图代码没有按预期工作。 这就是我所拥有的，问题可能集中在Ball对象的中间位置。 我发布了大部分程序，因为如果有人会运行它，它会编译/运行。
import java.awt.*; import java.applet.*; import java.awt.event.*; public class Bounce2 extends Applet implements ActionListener, AdjustmentListener, Runnable { //runtime variables boolean running = false; boolean kill = false; //buttons Button runbutton = new Button("Run"); Button pausebutton = new Button("Pause"); Button quitbutton = new Button("Quit"); //text Label speedlabel = new Label("Speed"); Label sizelabel = new Label("Size"); //scrollbars private final int barHeight = 20, SLIDER_WIDTH = 10, MAXSPEED = 110, MINSPEED = 0, MAX_SIZE = 110, MIN_SIZE = 10; Scrollbar speedbar = new Scrollbar(Scrollbar.HORIZONTAL, MAXSPEED/2, SLIDER_WIDTH, MINSPEED, MAXSPEED); Scrollbar sizebar = new Scrollbar(Scrollbar.HORIZONTAL, MAX_SIZE/2, SLIDER_WIDTH, MIN_SIZE, MAX_SIZE); //drawn objs Ball ball; int size = 50; private Graphics obj; Image offscreen = null; Point loc = new Point(100,100); //location of the ball private Thread ballThread; //boundaries int boundx = 640; int boundy = 400; //directions int dx = 1; //1 = left, -1 = right int dy = 1; //1 = up, -1 = down //speed int speed = speedbar.getValue(); int delay; //initialize the applet and draw everything public void init() { double colWeight[] = {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1};//15 cols double rowWeight[] = {1,1,1,1,1,1,1,1,1,1}; //10 rows int colWidth[] = {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1};//15 cols int rowHeight[] = {1,1,1,1,1,1,1,1,1,1}; //10 rows GridBagConstraints c = new GridBagConstraints(); GridBagLayout gbl = new GridBagLayout(); gbl.rowHeights = rowHeight; gbl.rowWeights = rowWeight; gbl.columnWeights = colWeight; gbl.columnWidths = colWidth; c.anchor = GridBagConstraints.CENTER; setBounds(0,0,480,640); setLayout(new BorderLayout()); Panel controlpanel = new Panel(); controlpanel.setLayout(gbl); controlpanel.setSize(640,80); Panel drawingpanel = new Panel(null); drawingpanel.setSize(640,400); ball = new Ball(); drawingpanel.add(ball); drawingpanel.setVisible(true); //speed scrollbar c.weightx = 1; c.weighty = 1; c.gridwidth = 3; c.gridheight = 1; c.gridx = 1; c.gridy = 7; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.speedbar,c); //run button c.weightx = 1; c.weighty = 1; c.gridwidth = 2; c.gridheight = 1; c.gridx = 5; c.gridy = 7; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.runbutton,c); //pause button c.weightx = 1; c.weighty = 1; c.gridwidth = 2; c.gridheight = 1; c.gridx = 8; c.gridy = 7; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.pausebutton,c); //size scrollbar c.weightx = 1; c.weighty = 1; c.gridwidth = 3; c.gridheight = 1; c.gridx = 11; c.gridy = 7; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.sizebar,c); //speed text label c.weightx = 1; c.weighty = 1; c.gridwidth = 3; c.gridheight = 1; c.gridx = 1; c.gridy = 8; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.speedlabel,c); //size text label c.weightx = 1; c.weighty = 1; c.gridwidth = 3; c.gridheight = 1; c.gridx = 11; c.gridy = 8; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.sizelabel,c); //quit button c.weightx = 1; c.weighty = 1; c.gridwidth = 3; c.gridheight = 1; c.gridx = 6; c.gridy = 9; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.quitbutton,c); //add to the screen controlpanel.add(this.speedbar); controlpanel.add(this.runbutton); controlpanel.add(this.pausebutton); controlpanel.add(this.sizebar); controlpanel.add(this.speedlabel); controlpanel.add(this.sizelabel); controlpanel.add(this.quitbutton); //add listners speedbar.addAdjustmentListener(this); runbutton.addActionListener(this); pausebutton.addActionListener(this); sizebar.addAdjustmentListener(this); quitbutton.addActionListener(this); //add the panels add("South", controlpanel); add("Center", drawingpanel); //drawing paramaters obj = drawingpanel.getGraphics(); loc = new Point(loc.x+dx, loc.y+dy); setVisible(true); validate(); } public void start() { if (ballThread == null) { ballThread = new Thread(this); ballThread.start(); repaint(); } } public void run() { Thread.currentThread().setPriority(Thread.MAX_PRIORITY); while (!kill) { if (running) { repaint(); } try { Thread.sleep(delay); } catch(InterruptedException e){System.err.println("Interrupted.");} } stop(); } //class to handle animations class Ball extends Canvas { public void move() { //if it will hit the right or left, flip the x direction and set it if (loc.x+size >= boundx || loc.x = boundy || loc.y = boundx) { newsize = boundx - loc.x - 1; sizebar.setValue(newsize); } // y if (loc.y+newsize >= boundy + 100) { newsize = boundy+100 - loc.y - 1; sizebar.setValue(newsize); } size = newsize; } if (source == speedbar) { speed = speedbar.getValue(); delay = MAXSPEED - speedbar.getValue(); } } public void stop() { this.speedbar.removeAdjustmentListener(this); this.runbutton.removeActionListener(this); this.pausebutton.removeActionListener(this); this.sizebar.removeAdjustmentListener(this); this.quitbutton.removeActionListener(this); Thread.currentThread().setPriority(Thread.MIN_PRIORITY); } }
这是正在运行的代码的修改版本。
import java.awt.*; import java.applet.*; import java.awt.event.*; public class Bounce2 extends Applet implements ActionListener, AdjustmentListener, Runnable { //runtime variables boolean running = false; boolean kill = false; //buttons Button runbutton = new Button("Run"); Button pausebutton = new Button("Pause"); Button quitbutton = new Button("Quit"); //text Label speedlabel = new Label("Speed"); Label sizelabel = new Label("Size"); Panel drawingpanel; //scrollbars private final int barHeight = 20, SLIDER_WIDTH = 10, MAXSPEED = 110, MINSPEED = 0, MAX_SIZE = 110, MIN_SIZE = 10; Scrollbar speedbar = new Scrollbar(Scrollbar.HORIZONTAL, MAXSPEED/2, SLIDER_WIDTH, MINSPEED, MAXSPEED); Scrollbar sizebar = new Scrollbar(Scrollbar.HORIZONTAL, MAX_SIZE/2, SLIDER_WIDTH, MIN_SIZE, MAX_SIZE); //drawn objs Ball ball; int size = 50; private Graphics obj; Image offscreen = null; Point loc = new Point(100,100); //location of the ball private Thread ballThread; //boundaries int boundx = 640; int boundy = 400; //directions int dx = 1; //1 = left, -1 = right int dy = 1; //1 = up, -1 = down //speed int speed = speedbar.getValue(); int delay = 3000; //initialize the applet and draw everything public void init() { double colWeight[] = {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1};//15 cols double rowWeight[] = {1,1,1,1,1,1,1,1,1,1}; //10 rows int colWidth[] = {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1};//15 cols int rowHeight[] = {1,1,1,1,1,1,1,1,1,1}; //10 rows GridBagConstraints c = new GridBagConstraints(); GridBagLayout gbl = new GridBagLayout(); gbl.rowHeights = rowHeight; gbl.rowWeights = rowWeight; gbl.columnWeights = colWeight; gbl.columnWidths = colWidth; c.anchor = GridBagConstraints.CENTER; setBounds(0,0,480,640); setLayout(new BorderLayout()); Panel controlpanel = new Panel(); controlpanel.setLayout(gbl); controlpanel.setSize(640,80); drawingpanel = new Panel(); drawingpanel.setSize(640,400); ball = new Ball(); drawingpanel.setLayout(new BorderLayout()); drawingpanel.add("Center",ball); //speed scrollbar c.weightx = 1; c.weighty = 1; c.gridwidth = 3; c.gridheight = 1; c.gridx = 1; c.gridy = 7; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.speedbar,c); //run button c.weightx = 1; c.weighty = 1; c.gridwidth = 2; c.gridheight = 1; c.gridx = 5; c.gridy = 7; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.runbutton,c); //pause button c.weightx = 1; c.weighty = 1; c.gridwidth = 2; c.gridheight = 1; c.gridx = 8; c.gridy = 7; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.pausebutton,c); //size scrollbar c.weightx = 1; c.weighty = 1; c.gridwidth = 3; c.gridheight = 1; c.gridx = 11; c.gridy = 7; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.sizebar,c); //speed text label c.weightx = 1; c.weighty = 1; c.gridwidth = 3; c.gridheight = 1; c.gridx = 1; c.gridy = 8; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.speedlabel,c); //size text label c.weightx = 1; c.weighty = 1; c.gridwidth = 3; c.gridheight = 1; c.gridx = 11; c.gridy = 8; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.sizelabel,c); //quit button c.weightx = 1; c.weighty = 1; c.gridwidth = 3; c.gridheight = 1; c.gridx = 6; c.gridy = 9; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.quitbutton,c); //add to the screen controlpanel.add(this.speedbar); controlpanel.add(this.runbutton); controlpanel.add(this.pausebutton); controlpanel.add(this.sizebar); controlpanel.add(this.speedlabel); controlpanel.add(this.sizelabel); controlpanel.add(this.quitbutton); //add listners speedbar.addAdjustmentListener(this); runbutton.addActionListener(this); pausebutton.addActionListener(this); sizebar.addAdjustmentListener(this); quitbutton.addActionListener(this); //add the panels add("South", controlpanel); add("Center", drawingpanel); //drawing paramaters loc = new Point(loc.x+dx, loc.y+dy); } public void start() { if (ballThread == null) { ballThread = new Thread(this); ballThread.start(); } } public void run() { Thread.currentThread().setPriority(Thread.MAX_PRIORITY); while (!kill) { if (running) { ball.invalidate(); ball.repaint(); } try { Thread.sleep(delay); } catch(InterruptedException e){System.err.println("Interrupted.");} } stop(); } public void paint(Graphics g){ super.paint(g); } //class to handle animations class Ball extends Canvas { public void move() { //if it will hit the right or left, flip the x direction and set it if (loc.x+size >= boundx || loc.x <= 0) { dx *= -1; } loc.x += dx; //if it will hit the top or bottom, flip the y direction and set it if (loc.y+size >= boundy || loc.y <= 0) { dy *= -1; } loc.y += dy; } public void update(Graphics g) { super.update(g); Graphics buffer; if (offscreen == null) { offscreen = createImage(getWidth(), getHeight()); } buffer = offscreen.getGraphics(); mypaint(buffer); g.drawImage(offscreen, 0, 0, this); } public void mypaint(Graphics g) { g.setColor(getBackground()); g.fillRect(loc.x,loc.y,boundx, boundy); //update loc move(); //draw g.setColor(Color.BLACK); g.drawOval(loc.x, loc.y, size, size); g.fillOval(loc.x, loc.y, size, size); //draw rectangles out of vector } } public void actionPerformed(ActionEvent e) { Object source = e.getSource(); if (source == this.runbutton) { running = true; } else if (source == this.pausebutton) { running = false; } else if (source == this.quitbutton) { //kill processes kill = true; //remove listeners stop(); } } public void adjustmentValueChanged(AdjustmentEvent e) { Object source = e.getSource(); //set the new size. if (source == sizebar) { //check for clipping int newsize = sizebar.getValue(); // x if (loc.x+newsize >= boundx) { newsize = boundx - loc.x - 1; sizebar.setValue(newsize); } // y if (loc.y+newsize >= boundy + 100) { newsize = boundy+100 - loc.y - 1; sizebar.setValue(newsize); } size = newsize; } if (source == speedbar) { speed = speedbar.getValue(); delay = MAXSPEED - speedbar.getValue(); } } public void stop() { this.speedbar.removeAdjustmentListener(this); this.runbutton.removeActionListener(this); this.pausebutton.removeActionListener(this); this.sizebar.removeAdjustmentListener(this); this.quitbutton.removeActionListener(this); Thread.currentThread().setPriority(Thread.MIN_PRIORITY); } }
我在您的代码中进行了以下更改，可以使其正常工作 –
首先，我将球的初始位置设置为
Point loc = new Point(10,10);
初始化ball = new Ball(); 添加 –
drawingpanel.setLayout(new BorderLayout()); drawingpanel.add("Center",ball);
在run（）方法重绘球 –
if(running){ ball.repaint(); }
在move（）方法中删除/注释行 –
//setBounds(dx,dy,size,size);
在更新（Graphics g）方法中删除/注释行 –
//buffer.setColor(Color.black); //buffer.fillRect(loc.x,loc.y,boundx, boundy);
的; if之后（offscreen == null）; 没有任何意义，所以我评论它 –
//if (offscreen == null);
宾果，一切都很好！ 如果你能够做到，请告诉我，否则我会发布更新后的代码。
将布局管理器添加到绘图面板：
drawingpanel.setLayout(new BorderLayout()); drawingpanel.add("Center",ball);
然后，调用ball.repaint(); 在run()方法中进入自定义更新方法。
最后，删除setBounds(dx,dy,size,size); 来自move()方法的语句。
最终的代码是这样的：
import java.awt.*; import java.applet.*; import java.awt.event.*; public class Bounce2 extends Applet implements ActionListener, AdjustmentListener, Runnable { //runtime variables boolean running = false; boolean kill = false; //buttons Button runbutton = new Button("Run"); Button pausebutton = new Button("Pause"); Button quitbutton = new Button("Quit"); //text Label speedlabel = new Label("Speed"); Label sizelabel = new Label("Size"); //scrollbars private final int barHeight = 20, SLIDER_WIDTH = 10, MAXSPEED = 110, MINSPEED = 0, MAX_SIZE = 110, MIN_SIZE = 10; Scrollbar speedbar = new Scrollbar(Scrollbar.HORIZONTAL, MAXSPEED/2, SLIDER_WIDTH, MINSPEED, MAXSPEED); Scrollbar sizebar = new Scrollbar(Scrollbar.HORIZONTAL, MAX_SIZE/2, SLIDER_WIDTH, MIN_SIZE, MAX_SIZE); //drawn objs Ball ball; int size = 50; private Graphics obj; Image offscreen = null; Point loc = new Point(100,100); //location of the ball private Thread ballThread; //boundaries int boundx = 640; int boundy = 400; //directions int dx = 1; //1 = left, -1 = right int dy = 1; //1 = up, -1 = down //speed int speed = speedbar.getValue(); int delay; //initialize the applet and draw everything public void init() { double colWeight[] = {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1};//15 cols double rowWeight[] = {1,1,1,1,1,1,1,1,1,1}; //10 rows int colWidth[] = {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1};//15 cols int rowHeight[] = {1,1,1,1,1,1,1,1,1,1}; //10 rows GridBagConstraints c = new GridBagConstraints(); GridBagLayout gbl = new GridBagLayout(); gbl.rowHeights = rowHeight; gbl.rowWeights = rowWeight; gbl.columnWeights = colWeight; gbl.columnWidths = colWidth; c.anchor = GridBagConstraints.CENTER; setBounds(0,0,480,640); setLayout(new BorderLayout()); Panel controlpanel = new Panel(); controlpanel.setLayout(gbl); controlpanel.setSize(640,80); Panel drawingpanel = new Panel(null); drawingpanel.setSize(640,400); ball = new Ball(); drawingpanel.setLayout(new BorderLayout()); drawingpanel.add("Center",ball); drawingpanel.setVisible(true); //speed scrollbar c.weightx = 1; c.weighty = 1; c.gridwidth = 3; c.gridheight = 1; c.gridx = 1; c.gridy = 7; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.speedbar,c); //run button c.weightx = 1; c.weighty = 1; c.gridwidth = 2; c.gridheight = 1; c.gridx = 5; c.gridy = 7; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.runbutton,c); //pause button c.weightx = 1; c.weighty = 1; c.gridwidth = 2; c.gridheight = 1; c.gridx = 8; c.gridy = 7; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.pausebutton,c); //size scrollbar c.weightx = 1; c.weighty = 1; c.gridwidth = 3; c.gridheight = 1; c.gridx = 11; c.gridy = 7; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.sizebar,c); //speed text label c.weightx = 1; c.weighty = 1; c.gridwidth = 3; c.gridheight = 1; c.gridx = 1; c.gridy = 8; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.speedlabel,c); //size text label c.weightx = 1; c.weighty = 1; c.gridwidth = 3; c.gridheight = 1; c.gridx = 11; c.gridy = 8; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.sizelabel,c); //quit button c.weightx = 1; c.weighty = 1; c.gridwidth = 3; c.gridheight = 1; c.gridx = 6; c.gridy = 9; c.fill= GridBagConstraints.HORIZONTAL; gbl.setConstraints(this.quitbutton,c); //add to the screen controlpanel.add(this.speedbar); controlpanel.add(this.runbutton); controlpanel.add(this.pausebutton); controlpanel.add(this.sizebar); controlpanel.add(this.speedlabel); controlpanel.add(this.sizelabel); controlpanel.add(this.quitbutton); //add listners speedbar.addAdjustmentListener(this); runbutton.addActionListener(this); pausebutton.addActionListener(this); sizebar.addAdjustmentListener(this); quitbutton.addActionListener(this); //add the panels add("South", controlpanel); add("Center", drawingpanel); //drawing paramaters obj = drawingpanel.getGraphics(); loc = new Point(loc.x+dx, loc.y+dy); setVisible(true); validate(); } public void start() { if (ballThread == null) { ballThread = new Thread(this); ballThread.start(); repaint(); } } public void run() { Thread.currentThread().setPriority(Thread.MAX_PRIORITY); while (!kill) { if (running) { repaint(); ball.repaint(); } try { Thread.sleep(delay); } catch(InterruptedException e){System.err.println("Interrupted.");} } stop(); } //class to handle animations class Ball extends Canvas { public void move() { //if it will hit the right or left, flip the x direction and set it if (loc.x+size >= boundx || loc.x <= 0) { dx *= -1; } loc.x += dx; //if it will hit the top or bottom, flip the y direction and set it if (loc.y+size >= boundy || loc.y <= 0) { dy *= -1; } loc.y += dy; // setBounds(dx,dy,size,size); } public void paint(Graphics g) { update(g); } public void update(Graphics g) { Graphics buffer; if (offscreen == null); { offscreen = createImage(boundx, boundy); buffer = offscreen.getGraphics(); } buffer.setColor(getBackground()); buffer.fillRect(loc.x,loc.y,boundx, boundy); //update loc move(); //draw buffer.setColor(Color.black); buffer.drawOval(loc.x, loc.y, size, size); buffer.fillOval(loc.x, loc.y, size, size); //draw rectangles out of vector super.paint(g); g.drawImage(offscreen, loc.x, loc.y, null); } } public void actionPerformed(ActionEvent e) { Object source = e.getSource(); if (source == this.runbutton) { running = true; } else if (source == this.pausebutton) { running = false; } else if (source == this.quitbutton) { //kill processes kill = true; //remove listeners stop(); } } public void adjustmentValueChanged(AdjustmentEvent e) { Object source = e.getSource(); //set the new size. if (source == sizebar) { //check for clipping int newsize = sizebar.getValue(); // x if (loc.x+newsize >= boundx) { newsize = boundx - loc.x - 1; sizebar.setValue(newsize); } // y if (loc.y+newsize >= boundy + 100) { newsize = boundy+100 - loc.y - 1; sizebar.setValue(newsize); } size = newsize; } if (source == speedbar) { speed = speedbar.getValue(); delay = MAXSPEED - speedbar.getValue(); } } public void stop() { this.speedbar.removeAdjustmentListener(this); this.runbutton.removeActionListener(this); this.pausebutton.removeActionListener(this); this.sizebar.removeAdjustmentListener(this); this.quitbutton.removeActionListener(this); Thread.currentThread().setPriority(Thread.MIN_PRIORITY); } }