JAVA 画图板实现（基本画图功能+界面UI）二、功能实现及重绘实现

上篇博客中介绍了界面的实现方法，在这篇博客中将对每个按钮的功能的实现进行讲解并介绍重绘

首先肯定要添加事件监听机制了，那么问题来了，事件源对象是谁？需要添加什么方法？事件接口是什么？

1、我们需要点击按钮，获取按钮上的文字信息，颜色信息，粗细信息。那么，此时事件源对象就是按钮，监听方法就是addActionListener(ActionListener e),事件接口就是ActionListener

2、要根据在窗体上按下和释放的位置画一个图形，此时事件源对象就是窗体，监听方法就是addMouseListener(MouseListener e)，事件接口就是MouseListener

 public class DrawListener extends MouseAdapter implements ActionListener {

     private Color color = Color.black;// 声明颜色属性，存储用户选择的颜色
     private int width = 1;// 声明粗细属性，存储用户选择的粗细
     private String type = "Line";// 声明图形属性，存储用户选择的图形
     private int x1, y1, x2, y2, x3 = 0, y3 = 0, x4 = 0, y4 = 0, x5, y5;// 声明坐标值属性，存储鼠标按下和释放的坐标值
     private Graphics2D g;// 声明画笔类属性，组件是画出来的，现在要在组件上画图形，Graphics从组件上获取
     private DrawMain dm;// 声明画图程序窗体组件属性
     private JTextField text;// 获取文本框内容
     private double H = 100;// 等腰三角形的高度
     private int num = 0;
     private List<Shape> list;
     private ImageIcon i = new ImageIcon("C:\\Users\\long452a\\Desktop\\a1.jpg");

     /**
      * 构造方法
      *
      * @param dm画图程序的窗体组件对象
      */
     public DrawListener(DrawMain dm, JTextField text, List<Shape> list) {
         this.dm = dm;
         this.text = text;
         this.list = list;
     }

     /**
      * 点击按钮时执行的事件处理方法
      *
      * @param e对象中存储了事件源对象的信息和动作信息
      */
     public void actionPerformed(ActionEvent e) {
     }

     /**
      * Invoked when the mouse button has been clicked (pressed and released) on a
      * component.
      */
     public void mouseClicked(MouseEvent e) {
     }

     /**
      * Invoked when a mouse button has been pressed on a component.
      */
     public void mousePressed(MouseEvent e) {
     }

     /**
      * Invoked when a mouse button has been released on a component.
      */
     public void mouseReleased(MouseEvent e) {
     }

     public void mouseDragged(MouseEvent e) {
     }
 }

这样我们的类就建好了，下面就该写里面的方法了

     /**
      * 点击按钮时执行的事件处理方法
      *
      * @param e对象中存储了事件源对象的信息和动作信息
      */
     public void actionPerformed(ActionEvent e) {
         String text = e.getActionCommand();
         if (text.equals("")) {
             JButton button = (JButton) e.getSource();
             color = button.getBackground();
         } else if (text.equals("1") || text.equals("3") || text.equals("5")) {
             width = Integer.parseInt(text);
         } else {
             type = text;
         }
         // System.out.println(color + ">>" + width + ">>" + type);
     }

     /**
      * Invoked when the mouse button has been clicked (pressed and released) on a
      * component.
      */
     public void mouseClicked(MouseEvent e) {
         x4 = x2;
         y4 = y2;
     }

     /**
      * Invoked when a mouse button has been pressed on a component.
      */
     public void mousePressed(MouseEvent e) {
         x1 = e.getX() + 7;
         y1 = e.getY() + 183;
         if (y1 < 183)
             y1 = 183;
         g = (Graphics2D) dm.getGraphics();// 从窗体上获取画笔对象
         g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);// 设置画笔抗锯齿
         g.setColor(color);// 设置画笔颜色
         g.setStroke(new BasicStroke(width));// 设置画笔线条粗细

     }

     /**
      * Invoked when a mouse button has been released on a component.
      */
     public void mouseReleased(MouseEvent e) {
         x2 = e.getX() + 7;
         y2 = e.getY() + 183;
         if (y2 < 183)
             y2 = 183;
         if (type.equals("iso_Tri")) {
             if (x1 == x2) {
                 g.drawLine(x1, y1, x2, y2);
                 g.drawLine(x1, y1, x1 + (int) H, (y2 + y1) / 2);
                 g.drawLine(x2, y2, x1 + (int) H, (y2 + y1) / 2);
                 list.add(new Shape(x1, y1, x2, y2, width, color, type, i, dm, text));
                 list.add(new Shape(x1, y1, x1 + (int) H, (y2 + y1) / 2, width, color, type, i, dm, text));
                 list.add(new Shape(x2, y2, x1 + (int) H, (y2 + y1) / 2, width, color, type, i, dm, text));
             } else if (y1 == y2) {
                 g.drawLine(x1, y1, x2, y2);
                 g.drawLine(x1, y1, (x1 + x2) / 2, y1 + (int) H);
                 g.drawLine(x2, y2, (x1 + x2) / 2, y1 + (int) H);
                 list.add(new Shape(x1, y1, x2, y2, width, color, type, i, dm, text));
                 list.add(new Shape(x1, y1, x1 + (x1 + x2) / 2, y1 + (int) H, width, color, type, i, dm, text));
                 list.add(new Shape(x2, y2, x1 + (x1 + x2) / 2, y1 + (int) H, width, color, type, i, dm, text));
             } else {
                 double a = Math.atan((double) (x2 - x1) / (double) (y2 - y1));
                 double x3 = (double) (x1 + x2) / 2 + H * Math.cos(a);
                 double y3 = (double) (y1 + y2) / 2 - H * Math.sin(a);
                 g.drawLine(x1, y1, x2, y2);
                 g.drawLine(x1, y1, (int) x3, (int) y3);
                 g.drawLine(x2, y2, (int) x3, (int) y3);
                 list.add(new Shape(x1, y1, x2, y2, width, color, type, i, dm, text));
                 list.add(new Shape(x1, y1, x1 + (int) x3, (int) y3, width, color, type, i, dm, text));
                 list.add(new Shape(x2, y2, (int) x3, (int) y3, width, color, type, i, dm, text));
             }
         } else if (type.equals("Polygon")) {
             if (num == 0) {
                 g.drawLine(x1, y1, x2, y2);
                 list.add(new Shape(x1, y1, x2, y2, width, color, type, i, dm, text));
                 x5 = x2;
                 y5 = y2;
             }
             num++;
             if (num == 1) {
                 x3 = x1;
                 y3 = y1;
             }
             if (x2 == x4 && y2 == y4) {
                 g.drawLine(x1, y1, x3, y3);
                 list.add(new Shape(x1, y1, x3, y3, width, color, type, i, dm, text));
                 num = 0;
             } else {
                 g.drawLine(x2, y2, x5, y5);
                 list.add(new Shape(x2, y2, x5, y5, width, color, type, i, dm, text));
                 x5 = x2;
                 y5 = y2;
             }
         } else {
             Shape s = new Shape(x1, y1, x2, y2, width, color, type, i, dm, text);
             s.draw(g);
             list.add(s);
         }
     }

     public void mouseDragged(MouseEvent e) {
         if (type.equals("Pencil")) {
             x2 = e.getX() + 7;//这里的+7 +183 是调出来的，能够使画的图是沿着鼠标
             y2 = e.getY() + 183;
             if (y2 < 183)
                 y2 = 183;
             Shape s = new Shape(x1, y1, x2, y2, width, color, type, i, dm, text);
             s.draw(g);
             list.add(s);
             x1 = x2;
             y1 = y2;
         } else if (type.equals("Erase")) {
             x2 = e.getX() + 7;
             y2 = e.getY() + 183;
             if (y2 < 183)
                 y2 = 183;
             Shape s = new Shape(x1, y1, x2, y2, width, Color.WHITE, type, i, dm, text);
             s.draw(g);
             list.add(s);
             x1 = x2;
             y1 = y2;
         } else if (type.equals("喷枪")) // 难点
         {
             Random rand = new Random();// 实例化一个随机数类的对象
             int size = rand.nextInt(50);// 随机决定要画的点数
             x2 = e.getX() + 7;
             y2 = e.getY() + 183;
             for (int j = 0; j < size; j++) {
                 // 在0-7之间可以取50次
                 int x = rand.nextInt(10);
                 int y = rand.nextInt(10);
                 // 不断改变（x1,y1）的坐标值，实现在(x1,y1)的周围画点
                 Shape s = new Shape(x2 + x, y2 + y, x2 + x, y2 + y, width, color, type, i, dm, text);
                 s.draw(g);
                 list.add(s);
                 x1 = x2;
                 y1 = y2;
             }
         }
     }

　　仔细看看代码，你也许注意到了，我在画图时创建了一个Shape对象，并且还把Shape对象存到了一个List中，为什么要这么做？你们可以去别人的博客上贴一个粗略实现的画图板代码，画几条直线然后再改变窗体的大小试试看，是不是画的直线不见了?那要怎么做才能使这些图形保存下来呢？这就需要用到重绘了。

　　但是，我们需要知道，为什么图形会消失？其实计算机中的界面什么都是画出来的。自然组件也是画出来的，而改变组件大小的时候，原来的组件无法满足现在组件的显示要求，所以组件要重新画一次，然而此时组件上的图形并不会重新再画一次，为什么？组件已经默认有重绘的方法了paint(Graphics g)，所以我们需要重写这个方法，但是我们怎么能让计算机知道之前画了什么呢?这是就需要把每次画的内容记录到队列或数组中，重绘时就可以根据这个队列或是数组进行了。而创建Shape对象自然是为了方便保存这些图形的数据了。

下面是Shape的写法

 public class Shape {

     private int x1, y1, x2, y2, width;
     private Color color;
     private String type;
     private ImageIcon i;
     private DrawMain dm;
     private JTextField text;

     public Shape(int x1, int y1, int x2, int y2, int width, Color color, String type, ImageIcon i, DrawMain dm,
             JTextField text) {
         this.x1 = x1;
         this.y1 = y1;
         this.x2 = x2;
         this.y2 = y2;
         this.width = width;
         this.color = color;
         this.type = type;
         this.i = i;
         this.dm = dm;
         this.text = text;
     }

     public void draw(Graphics2D g) {
         g.setColor(color);
         g.setStroke(new BasicStroke(width));
         if (type.equals("Line") || type.equals("Pencil") || type.equals("iso_Tri") || type.equals("Polygon")
                 || type.equals("Erase") || type.equals("喷枪")) {
             g.drawLine(x1, y1, x2, y2);
         } else if (type.equals("Oval")) {
             g.fillOval(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x2 - x1), Math.abs(y2 - y1));
         } else if (type.equals("Rect")) {
             g.drawRect(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x2 - x1), Math.abs(y2 - y1));
         } else if (type.equals("RoundRect")) {
             g.drawRoundRect(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x2 - x1), Math.abs(y2 - y1),
                     Math.abs(x2 - x1) / 3, Math.abs(y2 - y1) / 3);
         } else if (type.equals("fill3DRect")) {
             g.fill3DRect(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x2 - x1), Math.abs(y2 - y1), true);
         } else if (type.equals("fillArc")) {
             double r = ((x2 - x1) * (x2 - x1) + y1 * y1) / (2 * y1);
             double m = Math.asin((double) (x2 - x1) / r);
             g.fillArc(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x2 - x1), (int) r, 0, (int) (m * 180 / Math.PI));
         } else if (type.equals("Image")) {
             g.drawImage(i.getImage(), Math.min(x1, x2), Math.min(y1, y2), Math.abs(x2 - x1), Math.abs(y2 - y1), dm);
         } else if (type.equals("Text")) {
             g.drawString(text.getText(), x1, y1);
         }
     }

 }

现在还有一个问题，paint该写在哪？写在之前写的DrawMain中

private List<Shape> list = new ArrayList<Shape>();

    public void paint(Graphics gr) {
        super.paint(gr);
        Graphics2D g = (Graphics2D) gr;
        g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        for (int i = 0; i < list.size(); i++) {
            Shape shape = list.get(i);
            shape.draw(g);
        }
    }

提醒一下：别忘了把事件监听添加到组件中！！！！

这样一来，我们的画图板就能完美使用了。当然这个画图板跟系统中的比起来还是差了很多了，比如撤销、重做、保存等功能都还不具备，剩下的功能就需要后面慢慢研究再完善了。