Question

我有一个非常简单的程序，要求用户点击与其背景颜色相匹配的四个面板中的一个与较大面板（也称为displaypanel）的面板之一，随后将其背景颜色随机设置为四个中的一个。如果错误的面板点击Joptionpane出来; displaypanels background暂时设置为黑色。如果单击是，则displaypanel应重新设置其背景颜色。问题是我总是看不到背景正在更新。相反，有时候背景会保持黑色。 ...而更令人困惑的是，如果你在该程序的窗口上拖动另一个窗口，如果你看到颜色部分更新为显示面板上的移动或只是切换到另一个窗口并重新打开，那么它会保持黑色，那么你会看到完整更新的背景颜色。

那么为什么setMethod被调用但只是偶尔会被幕后的paint方法执行？为什么铸造其他窗户或框架使其可见？它与正在处理的鼠标点击事件有什么关系吗？

感谢所有人的解释，谢谢你们

public class MainPanel extends JPanel{


    Subpanel panel1;
    Subpanel panel2;
    Subpanel panel3;
    Subpanel panel4;
    Subpanel displaypanel;

    Color[] color; //stores all the  colors that display on the subpanels


    public static void main(String[] args) {
        JFrame window=new JFrame("This is a test");
        window.setContentPane(new MainPanel());
        window.setLocation(100,30);
        window.setSize(600,500);
        window.setVisible(true);

    }


    public MainPanel(){


        setLayout(new FlowLayout(FlowLayout.CENTER,80,30));


        panel1= new Subpanel();
        panel2= new Subpanel();
        panel3= new Subpanel();
        panel4= new Subpanel();

        //the big sub panel
        displaypanel= new Subpanel();

        color=new Color[4];
        color[0]=Color.BLUE;
        color[1]=Color.RED;
        color[2]=Color.YELLOW;
        color[3]=Color.GREEN;



        setBackground(Color.GRAY);
        displaypanel.setBackground(displayRandomColor());
        panel1.setBackground(color[0]);
        panel2.setBackground(color[1]);
        panel3.setBackground(color[2]);
        panel4.setBackground(color[3]); 

        displaypanel.setPreferredSize(new Dimension(400,250));
        panel1.setPreferredSize(new Dimension(70,70));
        panel2.setPreferredSize(new Dimension(70,70));
        panel3.setPreferredSize(new Dimension(70,70));
        panel4.setPreferredSize(new Dimension(70,70));

        add(displaypanel);
        add(panel1);
        add(panel2);
        add(panel3);
        add(panel4);





    }


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



    }

    public Color displayRandomColor(){
            Color i=Color.WHITE;
        switch ((int)(Math.random()*4)+1){
            case 1:
            i= Color.YELLOW;
            break;

            case 2:
            i= Color.BLUE;
            break;

            case 3:
            i= Color.GREEN;
            break;

            case 4:
            i= Color.RED;
        }   
        return i;
    }


    public class Subpanel extends JPanel{

        public Subpanel(){
                this.addMouseListener(new MouseAdapter(){
                public void mouseClicked(MouseEvent evt){
                    Component source=(Component)evt.getSource();

                        if((source.getBackground()).equals(displaypanel.getBackground())){
                            //do nothing for this test..
                    }
                        else{
                                displaypanel.setBackground(Color.BLACK);

                                //ask user to reset the background color
                                //**the following 2 lines introduces the problem
                            if(JOptionPane.showOptionDialog(null,"click Yes to see a new Color","Incorrect",JOptionPane.YES_NO_OPTION,JOptionPane.PLAIN_MESSAGE,null,null,null)==JOptionPane.YES_OPTION){
                                displaypanel.setBackground(displayRandomColor());

                            }
                        }

                        }





        });
        } //end of constructor
        public void paintComponent(Graphics g){
            super.paintComponent(g);

        }

    }

}

Answer 1

synchronized correctly时，您的计划运作良好。几点说明：

初始化对象一次，尽可能早在程序执行中。
使用Random的实例获取随机整数;请注意displayRandomColor()的简单实现。
```
private Color displayRandomColor() {
    return color[r.nextInt(color.length)];
}
```
应在event dispatch thread上仅构建和操作Swing GUI对象。
如果你真的想覆盖setPreferredSize()]，请不要使用getPreferredSize()，如建议here。
使用layouts和pack()封闭窗口。

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class MainPanel extends JPanel {

    private static final Random r = new Random();
    private final JPanel displayPanel;
    private Color[] color = {Color.RED, Color.GREEN, Color.BLUE, Color.YELLOW};
    private Subpanel panel1 = new Subpanel(color[0]);
    private Subpanel panel2 = new Subpanel(color[1]);
    private Subpanel panel3 = new Subpanel(color[2]);
    private Subpanel panel4 = new Subpanel(color[3]);

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                JFrame window = new JFrame("This is a test");
                window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                window.add(new MainPanel());
                window.pack();
                window.setLocationRelativeTo(null);
                window.setVisible(true);
            }
        });
    }

    public MainPanel() {
        setLayout(new BorderLayout());
        setBackground(Color.GRAY);

        //the big sub panel
        displayPanel = new JPanel() {

            @Override
            public Dimension getPreferredSize() {
                return new Dimension(320, 240);
            }
        };
        displayPanel.setBackground(displayRandomColor());

        //the control panel
        JPanel p = new JPanel();
        p.add(panel1);
        p.add(panel2);
        p.add(panel3);
        p.add(panel4);

        add(displayPanel, BorderLayout.CENTER);
        add(p, BorderLayout.SOUTH);
    }

    private Color displayRandomColor() {
        return color[r.nextInt(color.length)];
    }

    public class Subpanel extends JPanel {

        public Subpanel(Color color) {
            this.setBackground(color);
            this.addMouseListener(new MouseAdapter() {
                @Override
                public void mousePressed(MouseEvent evt) {
                    Component source = (Component) evt.getSource();
                    if ((source.getBackground()).equals(displayPanel.getBackground())) {
                        System.out.println(source.getBackground());
                    } else {
                        displayPanel.setBackground(Color.BLACK);
                        if (JOptionPane.showOptionDialog(null,
                            "Click Yes to see a new Color", "Incorrect",
                            JOptionPane.YES_NO_OPTION, JOptionPane.PLAIN_MESSAGE,
                            null, null, null) == JOptionPane.YES_OPTION) {
                            displayPanel.setBackground(displayRandomColor());
                        }
                    }
                }
            });
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(70, 70);
        }
    }
}

为什么不立即setBackground并在这个简单的程序中不断更新背景颜色

1 个答案: