如果通过递归函数调用paintComponent不起作用？ [英] paintComponent does not work if its called by the recursive function?

问题描述

1. 我希望一个接一个地看到所有 Points ，但我看到只能看到1
   点。我改变什么看到所有的点？


2. 在 System.out 中你可以看到10次设定然后2次
   paintComponent。每次设置后
   调用它会更改paintComponente？

1. I want to see all the Points one after another but I see only able to see 1 point. What shold I change to see all the Points ?
2. In the System.out you can see 10 times "set" and then 2 times "paintComponent". what should I change that after each time set is called it change the "paintComponente" ?

===== ================================================== ===========================

==================================================================================

public class exampe extends JPanel  
{
    int x; 
    int y;

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

        Graphics2D g2 = (Graphics2D) g;
        g2.fillOval(x-2,y-2,4,4);
        System.out.println("paintComponent");        
    }

    public void set(int X, int Y)
    {
        x = X;
        y = Y;
        System.out.println("set");
        super.repaint();
    }

    public static void main(String args[]) 
    {   
        int e=1;

        JFrame frame = new JFrame("TEST");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        exampe ex= new exampe();
        JScrollPane scroll = new JScrollPane(ex);
        frame.getContentPane().add(scroll);

        frame.setSize(400, 300);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);

        for(int i=0; i< 10; ++i)
            ex.set(e+i,e+i);         
    }
}

推荐答案

* 简单解释为什么你只能看到最后的更新：*

Chet Haase从肮脏的富客户那里采取的报价Romain Guy

It is important to note that repaint requests get "coalesced," or combined. 
So, for example, if you request a repaint and there is already one on the 
queue that has not yet been serviced, then the second request is ignored 
because your request for a repaint will already be fulfilled by the earlier 
request. This behavior is particularly helpful in situations where many
repaint requests are being generated, perhaps by very different situations 
and components, and Swing should avoid processing redundant requests and 
wasting effort.

试试这个，并询问您不清楚的事项：

Try your hands on this, and ask what is not clear to you :

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

public class PointsExample
{   
    private CustomPanel contentPane;
    private Timer timer;
    private int x = 1;
    private int y = 1;
    private ActionListener timerAction = new ActionListener()
    {   
        public void actionPerformed(ActionEvent ae)
        {
            contentPane.set(x, y);
            x++;
            y++;
            if (x == 450)
                timer.stop();
        }
    };
    /*
     * This is just JFrame, that we be 
     * using as the Base for our Application.
     * Though here we are calling our
     * JPanel (CustomPanel), whose
     * paintComponent(...) method, we had
     * override.
     */
    private void createAndDisplayGUI()
    {
        JFrame frame = new JFrame("Locate Mouse Position");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        contentPane = new CustomPanel();
        frame.setContentPane(contentPane);  
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
        timer = new Timer(100, timerAction);
        timer.start();
    }

    public static void main(String\u005B\u005D args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new PointsExample().createAndDisplayGUI();
            }
        });
    }
}

class CustomPanel extends JComponent
{
    private int x;
    private int y;

    public void set(int a, int b)
    {
        x = a;
        y = b;
        repaint();
    }   

    @Override
    public Dimension getPreferredSize()
    {
        return (new Dimension(500, 500));
    }

    @Override
    public void paintComponent(Graphics g)
    { 
        g.clearRect(0, 0, getWidth(), getHeight());
        Graphics2D g2 =(Graphics2D) g;
        g2.fillOval(x, y, 4, 4);        
    }
}

这是代码，允许你拥有在for循环中迭代时查看你的观点，尽管这种方法非常不鼓励，因为很多与之相关的缺点。虽然尝试了这个而不是调用 repaint（）调用 paintImmediately（int ...）或 paintImmediately（Rectangle rect）

Here is the code, that will allow you to have a look at your points while iterating inside a for loop, though this approach is highly discouraged, for many cons associated with it. Though try your hands on this instead of calling repaint() call paintImmediately(int ...) or paintImmediately(Rectangle rect)

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

public class PointsExample
{   
    private CustomPanel contentPane;
    private Timer timer;
    private int x = 1;
    private int y = 1;

    /*
     * This is just JFrame, that we be 
     * using as the Base for our Application.
     * Though here we are calling our
     * JPanel (CustomPanel), whose
     * paintComponent(...) method, we had
     * override.
     */
    private void createAndDisplayGUI()
    {
        JFrame frame = new JFrame("Locate Mouse Position");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        contentPane = new CustomPanel();
        frame.setContentPane(contentPane);  
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);

        for (int i = 0; i < 500; i++)
        {
            contentPane.set(x, y);
            x++;
            y++;
            if (x == 450)
                break;
        }
    }

    public static void main(String\u005B\u005D args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new PointsExample().createAndDisplayGUI();
            }
        });
    }
}

class CustomPanel extends JComponent
{
    private int x;
    private int y;

    public void set(int a, int b)
    {
        x = a;
        y = b;
        paintImmediately(0, 0, getWidth(), getHeight());

    }   

    @Override
    public Dimension getPreferredSize()
    {
        return (new Dimension(500, 500));
    }

    @Override
    public void paintComponent(Graphics g)
    { 
        super.paintComponent(g);
        g.fillOval(x, y, 4, 4);         
    }
}

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