Java 将 JPanel 传递给 child class

Question

我正在用 java 练习一些 OOP。

我只想用一些图形 objects 编写游戏，但我想用一些类来构建它。

整体布局应如下所示：

MainClass -> new MainPanel（扩展 JPanel）->new StartWindow（扩展包含游戏循环的抽象 GameWindow）

这样我应该可以创建 StartWindow、Level1Window、Level2Window 等等。我的 StartWindow 现在应该绘制第一层的布局。 StartWindow 将创建其他 objects（玩家、敌人等），稍后将负责绘制它们自己。

所以我想创建类似 "every object is responsible to draw itself"

的东西

我希望我能说清楚这应该如何工作。问题是，我不知道如何委派这个任务。

我的代码目前看起来像这样：

public class MainClass extends JFrame implements ActionListener {
    //..... other stuff
    public MainClass () {
        MainPanel mainPanel = new MainPanel();
    }
    //.... other stuff
}


class MainPanel extends JPanel {

    private GameWindow currentWindow;

    public MainPanel () {
        currentWindow = new StartWindow(this);
    }

    public void paintComponent(Graphics g) {
        g.drawRect (10, 10, 200, 200);  // <-- can see on the window
    }
}


abstract class GameWindow {
    // contains game loop and update functions and so on
}


public class StartWindow extends GameWindow {

    GamePanel _parentWindow;

    public StartWindow(GamePanel parentWindow) {
        super();
        _parentWindow = parentWindow;
    }

    public void paintComponent(Graphics g) {
        //Does not work
        g.drawRect (20, 20, 100, 100);  
    }
}

“_parentWindow”包含 MainPanel，因此我应该拥有在其面板上绘制所需的所有信息，但我不知道该怎么做。

编辑：有效的最小示例：

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class MainClass extends JFrame implements ActionListener {

public static void main(String[] args)
   {
       System.out.println("Program Window1");
       MainClass glt = new MainClass();
       glt.setVisible(true);
   }

//..... other stuff
public MainClass () {
    super("Fixed Timestep Game Loop Test");
    Container cp = getContentPane();
    cp.setLayout(new BorderLayout());
    JPanel p = new JPanel();
    p.setLayout(new GridLayout(1,2));



    System.out.println("Program Window2");
    MainPanel gamePanel= new MainPanel();

    cp.add(gamePanel, BorderLayout.CENTER);
    cp.add(p, BorderLayout.SOUTH);
    setSize(500, 500);
}
//.... other stuff

@Override
public void actionPerformed(ActionEvent arg0) {
    // TODO Auto-generated method stub

}
}


class MainPanel extends JPanel {

private GameWindow currentWindow;

public MainPanel () {
    currentWindow = new StartWindow(this);
}

public void paintComponent(Graphics g) {
    g.drawRect (0, 0, 200, 200);  // <-- can see on the window
}
}


abstract class GameWindow {
// contains game loop and update functions and so on
}


class StartWindow extends GameWindow {

MainPanel _parentWindow;

public StartWindow(MainPanel parentWindow) {
    super();
    _parentWindow = parentWindow;
}

public void paintComponent(Graphics g) {
    //Does not work
    g.drawRect (20, 20, 100, 100);  
}
}

Answer 1

在 MainPanel 的 paintComponent 方法中尝试类似的操作 class。

public void paintComponent(Graphics g) {
  g.drawRect (10, 10, 200, 200);  // <-- can see on the window
  Graphics2D g2d = (Graphics2D) g.create();
  ((StartWindow) currentWindow).paintComponent(g2d);
  g2d.dispose();
}

Answer 2

我会在您的主绘图 JComponent 中绘制精灵，例如，

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class MainClass extends JFrame implements ActionListener {

    public static void main(String[] args) {
        System.out.println("Program Window1");
        MainClass glt = new MainClass();
        glt.setVisible(true);
    }

    // ..... other stuff
    public MainClass() {
        super("Fixed Timestep Game Loop Test");
        setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        Container cp = getContentPane();
        cp.setLayout(new BorderLayout());
        JPanel p = new JPanel();
        p.setLayout(new GridLayout(1, 2));

        System.out.println("Program Window2");
        MainPanel gamePanel = new MainPanel();

        cp.add(gamePanel, BorderLayout.CENTER);
        cp.add(p, BorderLayout.SOUTH);
        setSize(500, 500);
    }

    // .... other stuff

    @Override
    public void actionPerformed(ActionEvent arg0) {
        // TODO Auto-generated method stub

    }
}

class MainPanel extends JPanel {

    private GameWindow currentWindow;

    public MainPanel() {
        currentWindow = new StartWindow(this);
    }

//    public void paintComponent(Graphics g) {
//        g.drawRect(0, 0, 200, 200); // <-- can see on the window
//    }

    // this should be protected, not public and should call super method 
    @Override  
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawRect(0, 0, 200, 200); // <-- can see on the window
        currentWindow.draw(g);
    }
}

interface Drawable {
    void draw(Graphics g);
}

abstract class GameWindow implements Drawable {
    // contains game loop and update functions and so on
}

class StartWindow extends GameWindow {

    MainPanel _parentWindow;

    public StartWindow(MainPanel parentWindow) {
        super();
        _parentWindow = parentWindow;
    }

    @Override
    public void draw(Graphics g) {
        g.setColor(Color.red);
        g.drawRect(20, 20, 100, 100);
    }
}

但我再次重申，不应继承游戏循环，而应传递其引用。通过组合而不是继承进行扩展。

或者甚至更好，让您的模型类实现一个接口，例如：

public interface Tickable {
    void tick(int deltaTime);
}

然后 List<Tickable> 等集合由主模型保存，每次游戏循环滴答时，它都会遍历列表，对列表中的每个项目调用 tick(...)。

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