当我运行此代码时，不会调用paintComponent方法 这可能是非常简单的错误，但我不知道为什么这样，PLZ。
package test;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.image.BufferedImage;
import javax.swing.BorderFactory;
import javax.swing.JPanel;
class Userboard extends JPanel
{
static BufferedImage image;
String shape;
Point start;
Point end;
Point mp;
String selected;
int ex,ey;//eraser
int w,h;
public Userboard()
{
setOpaque(false);
System.out.println("paper");
setBackground(Color.white);
setBorder(BorderFactory.createLineBorder(Color.black));
}
public void paintComponent(Graphics g)
{
System.out.println("userboard-paint");
try
{
//g.drawImage(image, 0, 0, this);
Graphics2D g2 = (Graphics2D)g;
g2.setPaint(Color.black);
if(start!=null && end!=null)
{
if(selected==("elipse"))
{
System.out.println("userboard-elipse");
g2.drawOval(start.x, start.y,(end.x-start.x),(end.y-start.y));
System.out.println("userboard-elipse drawn");
}
else if(selected==("rect"))
g2.drawRect(start.x, start.y, (end.x-start.x),(end.y-start.y));
else if(selected==("line"))
g2.drawLine(start.x,start.y,end.x,end.y);
}
}
catch(Exception e)
{}
}
//Function to draw the shape on image
public void draw()
{
System.out.println("Userboard-draw");
System.out.println(selected);
System.out.println(start);
System.out.println(end);
Graphics2D g2 = image.createGraphics();
g2.setPaint(Color.black);
if(start!=null && end!=null)
{
if(selected=="line")
g2.drawLine(start.x, start.y, end.x, end.y);
else if(selected=="elipse")
{
System.out.println("userboard-elipse");
g2.drawOval(start.x, start.y, (end.x-start.x),(end.y-start.y));
System.out.println("userboard-elipse drawn");
}
else if(selected=="rect")
g2.drawRect(start.x, start.y, (end.x-start.x),(end.y-start.y));
}
start=null;
repaint();
g2.dispose();
}
//To add the point to the board which is broadcasted by the server
public void addPoint(Point ps,String varname,String shape,String event)
{
try
{
if(end==null)
end = new Point();
if(start==null)
start = new Point();
if(shape.equals("elipse"))
this.selected="elipse";
else if(shape.equals("line"))
this.selected="line";
else if(shape.equals("rect"))
this.selected="rect";
else if(shape.equals("erase"))
erase();
if(end!=null && start!=null)
{
if(varname.equals("end"))
end=ps;
else if(varname.equals("mp"))
mp=ps;
else if(varname.equals("start"))
start=ps;
if(event.equals("drag"))
repaint();
else if(event.equals("release"))
draw();
}
repaint();
}
catch(Exception e)
{
e.printStackTrace();
}
}
//Function which provides the erase functionality
public void erase()
{
Graphics2D pic=(Graphics2D) image.getGraphics();
pic.setPaint(Color.white);
if(start!=null)
pic.fillRect(start.x, start.y, 10, 10);
}
//To set the size of the image
public void setWidth(int x,int y)
{
System.out.println("("+x+","+y+")");
w=x;
h=y;
image = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
}
//Function to add buttons into the panel, calling this function returns a panel
}
实例化用户板类的代码
public class Client extends Thread
{
Point point;
Paper paper;
Userboard userboard;
DatagramSocket datasocket=null;
public Client(DatagramSocket datasocket)
{
this.datasocket=datasocket;
}
//This function is to create the JFrame
public void createFrame()
{
JLayeredPane layerpane=new JLayeredPane();
JFrame frame=new JFrame("Whiteboard");
paper= new Paper(datasocket);
userboard=new Userboard();
frame.setLayout(new BorderLayout());
layerpane.setLayout(new BorderLayout());
layerpane.add(paper,BorderLayout.CENTER);
layerpane.add(userboard,BorderLayout.CENTER);//Panel where remote user draws
frame.add(paper.addButtons(),BorderLayout.WEST);
frame.add(layerpane,BorderLayout.CENTER);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(640, 480);
frame.addWindowListener(new WindowAdapter()
{
public void windowOpened(WindowEvent e) {}
public void windowClosing(WindowEvent e)
{
Draw draw=new Draw();
draw. close();
}
});
paper.setWidth(frame.getWidth(),frame.getHeight());
userboard.setWidth(frame.getWidth(),frame.getHeight());
frame.setVisible(true);
}
/*
* This function is overridden from the thread class
* This function listens for incoming packets from the server
* which contains the points drawn by the other client
*/
public void run ()
{
while (true)
{
try
{
byte[] buffer = new byte[512];
DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
datasocket.receive(packet);
InputStream in=new ByteArrayInputStream(packet.getData(), packet.getOffset(),packet.getLength());
DataInputStream din=new DataInputStream(in);
int x=din.readInt();
int y=din.readInt();
String varname=din.readLine();
String var[]=varname.split("-",3);
point=new Point(x,y);
userboard.addPoint(point, var[0], var[1],var[2]);
}
catch (IOException ex)
{
ex.printStackTrace();
}
}
}
//This function is to broadcast the newly drawn point to the server
public void broadcast (Point p,String varname,String shape,String event)
{
try
{
ByteArrayOutputStream baos=new ByteArrayOutputStream();
DataOutputStream dos=new DataOutputStream(baos);
dos.writeInt(p.x);
dos.writeInt(p.y);
dos.writeBytes(varname);
dos.writeBytes("-");
dos.writeBytes(shape);
dos.writeBytes("-");
dos.writeBytes(event);
dos.close();
byte[]data=baos.toByteArray();
InetAddress ip=InetAddress.getByName("10.123.97.125");
DatagramPacket packet=new DatagramPacket(data, data.length,ip , 8002);
datasocket.send(packet);
}
catch (Exception e)
{
e.printStackTrace();
}
}
}
答案 0 :(得分：2)
我认为您正在以错误的方式将两个面板添加到分层窗格中。
我建议你阅读tutorial for JLayeredPane。
添加到JLayeredPane时，不应该给出布局提示（在这种情况下不相关），而是要添加组件的图层的ID。
从教程：
for (int i = 0; i < ...number of labels...; i++) {
JLabel label = createColoredLabel(...);
layeredPane.add(label, new Integer(i));
...
}
在你的情况下，你可能想要这样的东西：
layerpane.add( paper, new Integer(0));
layerpane.add( userboard, new Integer(1));//Panel where remote user draws
我不保证这是唯一的问题，但是如果图层确实有问题，它可以解释为什么永远不会调用UserBoard.paintComponent（）方法。
答案 1 :(得分：0)
如果您只是将面板用于自己的绘图，那么只需覆盖绘图（Grapics）。我发现它更容易。如果您希望JPanel显示边框，请在绘图后调用paint（Graphics）中的paintBorder。