刷新 JComponent 倒计时不起作用

Question

我制作了这个示例来对 java 对话消息倒计时 30 秒。不知何故，消息组件没有刷新，直到现在我才明白为什么。如果时间正在更新并且组件重新绘制它应该可以工作。我尝试重新绘制 message.repaint() 和 messageFrame.repaint() 两个组件，但都没有工作。

下面的代码可以运行了。

import java.awt.Component;
import java.awt.Container;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.Toolkit;

import javax.swing.JFrame;
import javax.swing.JLabel;

public class Chronometer {


    private static final Insets INSETS = new Insets(1, 1, 1, 1);


public Chronometer(){

    double timeToNext = System.currentTimeMillis() + 30000;
        double timeDifference = 30000;

    JFrame messageFrame = new JFrame();
    messageFrame.setLayout(new GridBagLayout());
    messageFrame.setTitle("Warning");
    JLabel message = new JLabel("Preventing connection block. Next query in " + timeDifference/1000 + " seconds.");
    messageFrame.setSize(1000,1000);
    messageFrame.setLocationRelativeTo(null);
    addComponent(messageFrame, message, 0, 0, 1, 1, GridBagConstraints.CENTER, GridBagConstraints.CENTER);
    messageFrame.setVisible(true);

    while(timeDifference > 0){
        timeDifference = timeToNext - System.currentTimeMillis();
        messageFrame.repaint();
        //message.repaint();
    }
}


private static void addComponent(Container container, Component component, int gridx, int gridy,
        int gridwidth, int gridheight, int anchor, int fill) {

      GridBagConstraints gbc = new GridBagConstraints(gridx, gridy, gridwidth, gridheight, 1.0, 1.0,
    anchor, fill, INSETS, 0, 0);

      container.add(component, gbc);
      }


public static void main(String[] args){

Chronometer c = new Chronometer();
}

}

Answer 1

你走错路了。在构造函数中使用 while 循环是个坏主意。 您应该改用计时器，因为这正是 Chronometer 的含义。我拿了你的代码并用计时器快速重写了它，并利用观察者模式来更新标签。

使用实现 Observer 接口的控制器。

import java.awt.Component;
import java.awt.Container;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.util.Observable;
import java.util.Observer;

import javax.swing.JFrame;
import javax.swing.JLabel;

public class Controller implements Observer {
    private static final Insets INSETS = new Insets(1, 1, 1, 1);
    private Chronometer chrono = new Chronometer();
    private final JLabel message = new JLabel();

    public Controller() {
        final JFrame messageFrame = new JFrame("Warning");

        messageFrame.setLayout(new GridBagLayout());
        messageFrame.setSize(1000,1000);
        messageFrame.setLocationRelativeTo(null);

        addComponent(messageFrame, message, 0, 0, 1, 1, GridBagConstraints.CENTER, GridBagConstraints.CENTER);

        messageFrame.setVisible(true);

        chrono.addObserver(this);
    }

    public void startChrono(int delay) {
        chrono.startCountDown(delay);
    }

    public void refreshLabel() {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                message.setText("Preventing connection block. Next query in " + chrono.getTime()/1000 + " seconds.");
            }
        });
    }

    @Override
    public void update(Observable o, Object arg) {
        refreshLabel();
    }

    private static void addComponent(Container container, Component component, int gridx, int gridy, int gridwidth, int gridheight, int anchor, int fill) {
        GridBagConstraints gbc = new GridBagConstraints(gridx, gridy, gridwidth, gridheight, 1.0, 1.0,anchor, fill, INSETS, 0, 0);
        container.add(component, gbc);
    }
}

创建一个带有计时器的计时器类：

import java.util.Observable;
import java.util.Timer;
import java.util.TimerTask;

public class Chronometer extends Observable {

    private Timer timer = new Timer();
    private final int startTime = 30000;
    private int time = 30000;

    public void decreaseTime() {
        if (time > 0) time--;
    }

    public int getTime() {
        return time;
    }

    public void reset() {
        time = startTime;
    }

    public void startCountDown(int delay) {
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                decreaseTime();
                setChanged();
                notifyObservers();
            }
        }, delay,1);
    }
}

最后启动你的控制器

public class Main {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Controller().startChrono(1);
            }
        });
    }
}

Answer 2

我认为您需要手动更新 JLabel 文本。尝试像这样更改您的 while 循环：

 while(timeDifference > 0) {
     timeDifference = timeToNext - System.currentTimeMillis();
     message.setText("Preventing connection block. Next query in " + timeDifference/1000 + " seconds.");
 }