使用按钮启动动画 Java Swing

Question

我想在屏幕上创建几个对象 ("Spaceships") 的动画，并带有开始按钮。这是我目前所拥有的：

public class SpaceGame extends JPanel implements ActionListener {
    //The list of spaceships that should be painted
    LinkedList<Spaceship> playingList = new LinkedList<Spaceship>(); 
    Timer t = new Timer(5, this);

    @Override
    public void actionPerformed(ActionEvent e) {
        ListIterator<Spaceship> iter = playingList.listIterator();
        while (iter.hasNext()) {
            Spaceship s = iter.next();
            s.moveSpaceship();

        }
        repaint();
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);

        for (Spaceship s : playingList)
            s.drawSpaceship(g);
        t.start();
    }

    public static void main(String[] args) {
        SpaceGame game = new SpaceGame();
        JFrame fr = new JFrame();
        fr.setTitle("SPACE GAME");
        fr.setSize(990,690);
        fr.add(game);

        game.playingList .add(new Spaceship(3, 0, 570));
        game.playingList .add(new Spaceship(1, 250, 570));
        game.playingList .add(new Spaceship(2, 500, 570));


        JButton start = new JButton("START");
        start.addActionListener(game);
        fr.add(start,BorderLayout.SOUTH);

        fr.setVisible(true);
        fr.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    }

}

其中：

import java.awt.Graphics;

public class Spaceship {
    int initialSpeed;
    int locX, locY; //current location 

    public Spaceship(int initalSpeed, int initX, int initY) {
        this.initialSpeed = initalSpeed;
        locX = initX;
        locY = initY;
    }

    public void drawSpaceship(Graphics g) {
        g.setColor(Color.GREEN);
        g.fillOval(locX, locY, 100, 40);
    }

    public void moveSpaceship() {
        locY -= initialSpeed;
    }


}

当然，这个想法是按下按钮会触发动画。问题是动画会在没有按下开始按钮的情况下自动开始，然后当它结束时，按钮无效。我该如何解决这个问题？

Answer 1

让我们从显而易见的开始...

public void paintComponent(Graphics g) {
    super.paintComponent(g);

    for (Spaceship s : playingList)
        s.drawSpaceship(g);
    t.start();
}

在 paintComponent 中调用 t.start 是一个非常非常非常糟糕的主意。您无法控制绘制过程（即何时 paintComponent 被调用），因此它可能会出于各种原因随时被调用，通常是快速连续调用。

您应该查看 Painting in AWT and Swing 以了解有关 Swing 绘画工作原理的更多详细信息

绘制应该只绘制组件的当前状态，而不是其他任何东西。

第二个问题是 Timer 和按钮都在调用相同的 actionPerformed 方法，这实际上没有意义。事实上，在一个完美的世界中，你不会像这样直接实现 ActionListener 而是使用 Anonymous Classes 来防止外部类直接或间接调用该方法。

那么，解决方案是什么？向您的 SpaceGame 添加一个方法，可以调用它来启动动画，例如...

public class SpaceGame extends JPanel implements ActionListener {
  //The list of spaceships that should be painted

  LinkedList<Spaceship> playingList = new LinkedList<Spaceship>();
  Timer t = new Timer(5, this);

  public void start() {
    if (t.isRunning()) {
      return;
    }
    t.start();
  }

  @Override
  public void actionPerformed(ActionEvent e) {
    ListIterator<Spaceship> iter = playingList.listIterator();
    while (iter.hasNext()) {
      Spaceship s = iter.next();
      s.moveSpaceship();

    }
    repaint();
  }

  public void paintComponent(Graphics g) {
    super.paintComponent(g);

    for (Spaceship s : playingList) {
      s.drawSpaceship(g);
    }
  }

  public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
      @Override
      public void run() {
        SpaceGame game = new SpaceGame();
        JFrame fr = new JFrame();
        fr.setTitle("SPACE GAME");
        // This is unadvisable :/
        fr.setSize(990, 690);
        fr.add(game);

        game.playingList.add(new Spaceship(3, 0, 570));
        game.playingList.add(new Spaceship(1, 250, 570));
        game.playingList.add(new Spaceship(2, 500, 570));

        JButton start = new JButton("START");
        start.addActionListener(new ActionListener() {
          @Override
          public void actionPerformed(java.awt.event.ActionEvent e) {
            game.start();
          }
        });
        fr.add(start, BorderLayout.SOUTH);

        fr.setVisible(true);
        fr.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      }
    });
  }
}

然后更新您的主要方法以调用它...

public static void main(String[] args) {
  EventQueue.invokeLater(new Runnable() {
    @Override
    public void run() {
      SpaceGame game = new SpaceGame();
      JFrame fr = new JFrame();
      fr.setTitle("SPACE GAME");
      // This is unadvisable :/
      fr.setSize(990, 690);
      fr.add(game);

      game.playingList.add(new Spaceship(3, 0, 570));
      game.playingList.add(new Spaceship(1, 250, 570));
      game.playingList.add(new Spaceship(2, 500, 570));

      JButton start = new JButton("START");
      start.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(java.awt.event.ActionEvent e) {
          game.start();
        }
      });
      fr.add(start, BorderLayout.SOUTH);

      fr.setVisible(true);
      fr.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
  });
}

使用按钮启动动画 Java Swing

Starting animation with a button Java Swing

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swing

button

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