Question

我有一个用于扩展JPanel动画的类的Timer，ActionListener监听它并使actionPerformed运行，它会重新绘制并在需要时停止计时器。但启动计时器animatePanel的方法在计时器运行时继续执行，这是我不想要的。我希望它等到计时器停止返回。

Timer在类的构造函数中初始化，如下所示：

timer = new Timer(5, taskPerformer);

这就是它的作用。我有一些东西叫animatePanel（）：

    private ActionListener taskPerformer = new ActionListener() {
    public void actionPerformed(ActionEvent evt) {
        ...
        if (some conditions){
            ...
            timer.stop();
            ...
            return;
        }

        ...
    }
};

private void animatePanel() {
    ...
    timer.start();
    System.out.println("Timer stopped."); //always executes before the timer has stopped :(
    //then returns and lets the rest of my program run while the timer is still going, which is BAD
}

计时器工作正常，但在某些情况下，animatePanel（）会很快返回并让程序的其余部分运行，从而导致出现问题。

Answer 1

您不能在事件调度线程的上下文中执行此操作，这样做会使应用程序挂起！

计时器必须在单独的Thread中启动。这样就可以利用线程监控API。

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class WaitForTimer {

    public static void main(String[] args) {
        new WaitForTimer();
    }

    public WaitForTimer() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public static class TestPane extends JPanel {

        protected static final Object WAIT_FOR = new Object();
        private Timer timer;
        private int tickCount = 0;
        private JLabel ticks;
        private JButton start;

        public TestPane() {
            timer = new Timer(250, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    tickCount++;
                    if (tickCount > 10) {
                        tickCount = 0;
                        timer.stop();
                        synchronized (WAIT_FOR) {
                            WAIT_FOR.notifyAll();
                        }
                        start.setEnabled(true);
                    }
                    ticks.setText(String.valueOf(tickCount));
                }
            });
            timer.setRepeats(true);
            timer.setCoalesce(true);

            ticks = new JLabel("...");
            start = new JButton("Start");

            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridwidth = GridBagConstraints.REMAINDER;
            add(ticks, gbc);
            add(start, gbc);

            start.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    start.setEnabled(false);
                    new Thread(new Runnable() {
                        @Override
                        public void run() {
                            System.out.println("Starting timer...");
                            timer.start();
                            synchronized (WAIT_FOR) {
                                try {
                                    WAIT_FOR.wait();
                                } catch (InterruptedException ex) {
                                }
                            }
                            System.out.println("Timer finished...");
                        }
                    }).start();
                }
            });

        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }
    }
}

如何在执行代码之前等待计时器停止？

1 个答案: