Java Jpanel重涂/更新问题

Question

i have a problem with the method Repaint of my jpanel. I'm trying to make a "Racing game" with the Java Swing and by following the MVC architecture :

i have 5 classes : Main : runs the MVC

public class Main {
    private static Model model;
    private static View view;
    private static Controller controller;

    public static void main(String[] args) {
        model = new Model();
        view =  new View();
        controller = new Controller();

        model.addObserver(view);

        controller.addModule(model);
        controller.addView(view);

        view.addContoller(controller);
    }
}

Model :

import java.util.ArrayList;
import java.util.Observable;


public class Model extends Observable{
    private ArrayList<Car> cars;// List of cars

    public Model() {
        cars = new ArrayList<Car>();
        cars.add(new Car(this,0, 50));
        cars.add(new Car(this,0, 50));
        cars.add(new Car(this,0, 50));
    }

    public void startCar(int i){
        //i is the index of the selected element in the checkbox
        //if i==0 then the selected element is "All cars" else is a specific car
        if(i>0)
            cars.get(i-1).start();
        else{
            for(int j=0;j<cars.size();j++)
                cars.get(j).start();
        }
    }

    public void speedUpCar(int i) {
        if(i>0)
            cars.get(i-1).incVitess();
        else{
            for(int j=0;j<cars.size();j++)
                cars.get(j).incVitess();
        }
    }

    public void notifyView(){
        setChanged();
        notifyObservers(cars);
    }

    public void speedDownCar(int i) {
        if(i>0)
            cars.get(i-1).decVitess();
        else{
            for(int j=0;j<cars.size();j++)
                cars.get(j).decVitess();
        }
    }

    public void stopCar(int i) {
        if(i>0)
            cars.get(i-1).stop();
        else{
            for(int j=0;j<cars.size();j++)
                cars.get(j).stop();
        }
    }
}

the View :

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.GridLayout;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.util.ArrayList;
import java.util.Observable;
import java.util.Observer;
import java.util.Vector;

import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;


public class View implements Observer {
    private JFrame fen;
    private JPanel btnPanel,panel;
    private JButton play,speedUp,speedDown,stop;
    private JComboBox<String> listeCar;
    private boolean test = false;

    public View() {
        fen = new JFrame();
        fen.setTitle("Car Racing");
        fen.setSize(900, 400);
        fen.setLocationRelativeTo(null);
        fen.setResizable(false);

        Vector<String> v = new Vector<String>();
        v.add("All cars");v.add("car 1");v.add("car 2");v.add("car 3");
        listeCar = new JComboBox<String>(v);

        play = new JButton("Play");
        speedUp = new JButton("+");
        speedDown = new JButton("-");
        stop = new JButton("stop");

        panel = new JPanel(new GridLayout(3,1));
        btnPanel = new JPanel();

        btnPanel.add(listeCar);
        btnPanel.add(play);
        btnPanel.add(speedUp);
        btnPanel.add(speedDown);
        btnPanel.add(stop);

        Container c = fen.getContentPane();

        c.setLayout(new BorderLayout());

        c.add(btnPanel, BorderLayout.SOUTH);
        c.add(panel, BorderLayout.CENTER);

        fen.setVisible(true);

        fen.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });


    }

    public void addContoller(Controller controller){
        play.addActionListener(controller);
        speedUp.addActionListener(controller);
        speedDown.addActionListener(controller);
        stop.addActionListener(controller);
    }

    @Override
    public void update(Observable arg0, Object c) {
        ArrayList<Car> cars = (ArrayList<Car>)c;
        for(int i=0;i<cars.size();i++){
            Car car = cars.get(i);
            if(!test){ // if its the first tima, add the cars to the panel
                panel.add(car);
            }else{
                car.repaint(); // << the Problem is HERE
            }
        }
        test = true;
    }

    public JButton getPlay() {
        return play;
    }

    public JButton getSpeedUp() {
        return speedUp;
    }

    public JButton getSpeedDown() {
        return speedDown;
    }

    public JButton getStop() {
        return stop;
    }

    public JComboBox<String> getListeCar() {
        return listeCar;
    }
}

The controller:

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;


public class Controller implements ActionListener{
    private Model model;
    private View view;

    public Controller() {

    }

    public void addModule(Model m) {
        model = m;
        model.notifyView();
    }

    public void addView(View v){
        view = v;
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if(e.getSource() == view.getPlay()){
            model.startCar(view.getListeCar().getSelectedIndex());
        }else if(e.getSource() == view.getSpeedUp()){
            model.speedUpCar(view.getListeCar().getSelectedIndex());
        }else if(e.getSource() == view.getSpeedDown()){
            model.speedDownCar(view.getListeCar().getSelectedIndex());
        }else if(e.getSource() == view.getStop()){
            model.stopCar(view.getListeCar().getSelectedIndex());
        }
    }
}

The car class :

import java.awt.Color;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;
import javax.swing.JPanel;


public class Car extends JPanel{
    private int id,x,y,vitess;
    private Thread thread;
    private Model model;
    private boolean start = true;
    private boolean forward = true;
    private Color color;
    private boolean threadStarted = false;
    private BufferedImage bg; // background image

    public Car(Model model,int x,int y) {
        this.x =x;
        this.y = y;
        vitess = 7;
        this.model = model;

        try {
            bg = ImageIO.read(new File("road.png"));
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        color = changeColor(); // Random color

        thread = new Thread(new CarThread(this));

        start();
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(bg, 0, 0, null); 
        g.setColor(color);
        g.fillRect(x, y, 100, 50); // the car is a simple rectangle
    }

    public void start() {
        start = true;
        if(!threadStarted){
            threadStarted = true;
            thread.start();
        }else{
            thread.resume();
        }
    }

    public void move(){
        System.out.println("X:"+x);
        if(forward){
            if(x<this.getWidth()){
                x+=2;
            }else{
                color = changeColor();
                forward = false;
            }
        }else{
            if(x>0){
                x-=2;
            }else{
                color = changeColor();
                forward = true;
            }
        }

        model.notifyView();
    }

    private Color changeColor() {
        int r = (int)(Math.random()*255);
        int g = (int)(Math.random()*255);
        int b = (int)(Math.random()*255);
        return new Color(r,g,b);
    }

    public void stop(){
        start = false;
        thread.suspend();
    }

    public void incVitess(){
        if(vitess>1)
            vitess--;
    }

    public void decVitess(){
        if(vitess<6)
            vitess++;
    }

    public int getId() {
        return id;
    }


    public int getX() {
        return x;
    }

    public int getY() {
        return y;
    }

    public int getVitess() {
        return vitess;
    }   

    public boolean getStart(){
        return start;
    }

    public void setStart(boolean m){
        this.start = m;
    }

    public Color getColor(){
        return color;
    }
}

CarThraed class:

public class CarThread implements Runnable{
    private Car car;

    public CarThread(Car car) {
        this.car = car;
    }

    @Override
    public void run() {
        while(car.getStart()){
            car.move();
            try {
                Thread.sleep(car.getVitess());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

    }
}

if you run the project you will note that the cars does not reach the end of the frame, even if used:

if(x<this.getWidth()) x++;

but when i replace

car.repaint(); // << the Problem is HERE

with

car.update(car.getGraphics()); // << the Problem is HERE

the cars can now reach the end of the Frame, but the buttons in the btnJpanel disappear

image with repaint here image with update here

thank you in advance

Answer 1

I can't say that I've read all your code, but your model never notifies the view. I mean nowhere inside of the model class's code is the notifyView() method called. It should be the model's responsibility to call this whenever its state is changed.

Note that this:

car.update(car.getGraphics()); // << the Problem is HERE

Should not be used as the Graphics obtained is not stable.

Also, your model holds view components, an ArrayList of Car, a class that extends JPanel, another thing that should never occur as the model should be completely ignorant of the view, with the exception being that it knows that some things may be listening to it, and it needs to notify those things, and that's it. Instead your Model should hold an ArrayList of non-view, non-JPanel logical Car objects.

---

Edit
You state:

In the model i have the method: public void notifyView() which is called by the car's method public void Move() , That means whenever the thread calls the move method of the car, it calls the notifyView of the model

No, the Car should not be calling this method -- only the model itself should call this when its state is changed.

Also, I see that you've got very dangerous code using Thread#suspend() and Thread#resume() method calls. These methods have been deprecated as they've been found to be dangerous. To find out why, please check the API for Thread as well as this useful article . You will most definitely want to avoid their use.

---

Suggestions

• Make Car a logical non-GUI class that knows its position and can have its position changed.
• Override your drawing JPanels protected void paintComonent(Graphics g) method and use the Car information from the model to draw the Cars. In other words, use the state of the model to affect the state of the view.
• Use a Swing Timer instead of a background thread, to change your Car positions.
• Have the model and only the model call the notifyView method when its state has been changed.

---

Edit
Your main bug is here:

class Car extends JPanel {
    private int id, x, y, vitess;

    //....

    public int getX() {
       return x;
    }

    public int getY() {
       return y;
    }

You're inadvertently overriding the Car JPanel's getX and getY methods, messing up the location of these components. This is another reason to avoid overriding Swing components unless necessary -- to avoid these hidden side effects.

Get rid of or rename these methods.