用Java创建"paint"应用程序

Question

我有一个数组列表,跟踪"点",并使用数组来跟踪不同的大小.通过mouseWheelListener更改大小,并将更改保存在该数组中.但是由于某些原因,所有的点都被调整大小,这不是我想要的.在经历了几次之后,一切看起来都应该有效但我必须错过一些简单的东西.我的代码如下.

//********************************************************************
//  DotsPanel.java           
//  Represents the primary panel for the Dots program.
//********************************************************************

import java.util.ArrayList;

import javax.swing.JPanel;

import java.awt.*;
import java.awt.event.*;

public class DotsPanel extends JPanel
{
    private int SIZE = 10;  // radius of each dot
    private int[] dotSizes = new int[10000];
    int i = 0;

    private ArrayList<Point> pointList;

    //-----------------------------------------------------------------
    //  Constructor: Sets up this panel to listen for mouse events.
    //-----------------------------------------------------------------
    public DotsPanel()
    {
        pointList = new ArrayList<Point>();

        addMouseListener (new DotsListener());
        addMouseMotionListener(new DotsListener());
        addMouseWheelListener(new DotsListener());

        setBackground(Color.red);
        setPreferredSize(new Dimension(300, 200));
    }

    //-----------------------------------------------------------------
    //  Draws all of the dots stored in the list.
    //-----------------------------------------------------------------
    public void paintComponent(Graphics page)
    {
        super.paintComponent(page);

        page.setColor(Color.cyan);

        for (Point spot : pointList)
            //change size to sizes[n]
            page.fillOval(spot.x-dotSizes[pointList.size()-1], spot.y-dotSizes[pointList.size()-1], dotSizes[pointList.size()-1]*2, dotSizes[pointList.size()-1]*2);

        page.drawString("Count: " + pointList.size(), 5, 15);
    }

    //*****************************************************************
    //  Represents the listener for mouse events.
    //*****************************************************************
    private class DotsListener implements MouseListener, MouseMotionListener, MouseWheelListener
    {
        //--------------------------------------------------------------
        //  Adds the current point to the list of points and redraws
        //  the panel whenever the mouse button is pressed.
        //--------------------------------------------------------------
        public void mousePressed(MouseEvent event)
        {
            pointList.add(event.getPoint());
            repaint();
        }

        //--------------------------------------------------------------
        //  Provide empty definitions for unused event methods.
        //--------------------------------------------------------------
        public void mouseClicked(MouseEvent event) {}
        public void mouseReleased(MouseEvent event) {}
        public void mouseEntered(MouseEvent event) {}
        public void mouseExited(MouseEvent event) {}

        @Override
        public void mouseDragged(MouseEvent event) 
        {
            pointList.add(event.getPoint());
            dotSizes[pointList.size()-1] = SIZE;
            //store size of dot here
            repaint();

        }

        @Override
        public void mouseMoved(MouseEvent event) {}

        @Override
        public void mouseWheelMoved(MouseWheelEvent event) 
        {
            SIZE -= event.getWheelRotation();
            repaint();
        }
    }
}

Answer 1

在这段代码中:

for (Point spot : pointList)
    //change size to sizes[n]
    page.fillOval(spot.x-dotSizes[pointList.size()-1], spot.y-dotSizes[pointList.size()-1], dotSizes[pointList.size()-1]*2, dotSizes[pointList.size()-1]*2);

您对所有点使用单点大小:添加的最后一个点的大小.(甚至还有一个注释可以解决这个问题!)你需要使用索引进行迭代,这样你就可以索引dotSizes数组以及pointList ArrayList:

for (int i = 0; i < pointList.size(); ++i) {
    Point spot = pointList.get(i);
    int size = dotSizes[i];
    page.fillOval(spot.x-size, spot.y-size, size*2, size*2);
}

这将是更好的"用大小点",它封装了一个类定义自己Point和size:

class Spot extends Point {
    public int size;
    public Spot(int x, int y, int size) {
        super(x, y);
        this.size = size;
    }
}

然后将您更改pointList为a,ArrayList<Spot>然后您可以返回迭代单个列表:

for (Spot spot : pointList)
    page.fillOval(spot.x-spot.size, spot.y-spot.size, 2*dot.size, 2*dot.size);

当然,您还必须更新相应地向列表添加点的代码.

顺便说mousePressed一句,在我看来,你的处理程序有一个错误:它在添加一个点时不会添加大小.切换到Spot课程也有助于避免这种问题.