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
1 public class DrawListener extends MouseAdapter implements ActionListener { 2 3 private Color color = Color.black;// 声明颜色属性，存储用户选择的颜色 4 private int width = 1;// 声明粗细属性，存储用户选择的粗细 5 private String type = "Line";// 声明图形属性，存储用户选择的图形 6 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 7 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 8 private DrawMain dm;// 声明画图程序窗体组件属性 9 private JTextField text;// 获取文本框内容 10 private double H = 100;// 等腰三角形的高度 11 private int num = 0; 12 private List<Shape> list; 13 private ImageIcon i = new ImageIcon("C:\Users\long452a\Desktop\a1.jpg"); 14 15 /** 16 * 构造方法 17 * 18 * @param dm画图程序的窗体组件对象 19 */ 20 public DrawListener(DrawMain dm, JTextField text, List<Shape> list) { 21 this.dm = dm; 22 this.text = text; 23 this.list = list; 24 } 25 26 /** 27 * 点击按钮时执行的事件处理方法 28 * 29 * @param e对象中存储了事件源对象的信息和动作信息 30 */ 31 public void actionPerformed(ActionEvent e) { 32 } 33 34 /** 35 * Invoked when the mouse button has been clicked (pressed and released) on a 36 * component. 37 */ 38 public void mouseClicked(MouseEvent e) { 39 } 40 41 /** 42 * Invoked when a mouse button has been pressed on a component. 43 */ 44 public void mousePressed(MouseEvent e) { 45 } 46 47 /** 48 * Invoked when a mouse button has been released on a component. 49 */ 50 public void mouseReleased(MouseEvent e) { 51 } 52 53 public void mouseDragged(MouseEvent e) { 54 } 55 }
这样我们的类就建好了，下面就该写里面的方法了
1 /** 2 * 点击按钮时执行的事件处理方法 3 * 4 * @param e对象中存储了事件源对象的信息和动作信息 5 */ 6 public void actionPerformed(ActionEvent e) { 7 String text = e.getActionCommand(); 8 if (text.equals("")) { 9 JButton button = (JButton) e.getSource(); 10 color = button.getBackground(); 11 } else if (text.equals("1") || text.equals("3") || text.equals("5")) { 12 width = Integer.parseInt(text); 13 } else { 14 type = text; 15 } 16 // System.out.println(color + ">>" + width + ">>" + type); 17 } 18 19 /** 20 * Invoked when the mouse button has been clicked (pressed and released) on a 21 * component. 22 */ 23 public void mouseClicked(MouseEvent e) { 24 x4 = x2; 25 y4 = y2; 26 } 27 28 /** 29 * Invoked when a mouse button has been pressed on a component. 30 */ 31 public void mousePressed(MouseEvent e) { 32 x1 = e.getX() + 7; 33 y1 = e.getY() + 183; 34 if (y1 < 183) 35 y1 = 183; 36 g = (Graphics2D) dm.getGraphics();// 从窗体上获取画笔对象 37 g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);// 设置画笔抗锯齿 38 g.setColor(color);// 设置画笔颜色 39 g.setStroke(new BasicStroke(width));// 设置画笔线条粗细 40 41 } 42 43 /** 44 * Invoked when a mouse button has been released on a component. 45 */ 46 public void mouseReleased(MouseEvent e) { 47 x2 = e.getX() + 7; 48 y2 = e.getY() + 183; 49 if (y2 < 183) 50 y2 = 183; 51 if (type.equals("iso_Tri")) { 52 if (x1 == x2) { 53 g.drawLine(x1, y1, x2, y2); 54 g.drawLine(x1, y1, x1 + (int) H, (y2 + y1) / 2); 55 g.drawLine(x2, y2, x1 + (int) H, (y2 + y1) / 2); 56 list.add(new Shape(x1, y1, x2, y2, width, color, type, i, dm, text)); 57 list.add(new Shape(x1, y1, x1 + (int) H, (y2 + y1) / 2, width, color, type, i, dm, text)); 58 list.add(new Shape(x2, y2, x1 + (int) H, (y2 + y1) / 2, width, color, type, i, dm, text)); 59 } else if (y1 == y2) { 60 g.drawLine(x1, y1, x2, y2); 61 g.drawLine(x1, y1, (x1 + x2) / 2, y1 + (int) H); 62 g.drawLine(x2, y2, (x1 + x2) / 2, y1 + (int) H); 63 list.add(new Shape(x1, y1, x2, y2, width, color, type, i, dm, text)); 64 list.add(new Shape(x1, y1, x1 + (x1 + x2) / 2, y1 + (int) H, width, color, type, i, dm, text)); 65 list.add(new Shape(x2, y2, x1 + (x1 + x2) / 2, y1 + (int) H, width, color, type, i, dm, text)); 66 } else { 67 double a = Math.atan((double) (x2 - x1) / (double) (y2 - y1)); 68 double x3 = (double) (x1 + x2) / 2 + H * Math.cos(a); 69 double y3 = (double) (y1 + y2) / 2 - H * Math.sin(a); 70 g.drawLine(x1, y1, x2, y2); 71 g.drawLine(x1, y1, (int) x3, (int) y3); 72 g.drawLine(x2, y2, (int) x3, (int) y3); 73 list.add(new Shape(x1, y1, x2, y2, width, color, type, i, dm, text)); 74 list.add(new Shape(x1, y1, x1 + (int) x3, (int) y3, width, color, type, i, dm, text)); 75 list.add(new Shape(x2, y2, (int) x3, (int) y3, width, color, type, i, dm, text)); 76 } 77 } else if (type.equals("Polygon")) { 78 if (num == 0) { 79 g.drawLine(x1, y1, x2, y2); 80 list.add(new Shape(x1, y1, x2, y2, width, color, type, i, dm, text)); 81 x5 = x2; 82 y5 = y2; 83 } 84 num++; 85 if (num == 1) { 86 x3 = x1; 87 y3 = y1; 88 } 89 if (x2 == x4 && y2 == y4) { 90 g.drawLine(x1, y1, x3, y3); 91 list.add(new Shape(x1, y1, x3, y3, width, color, type, i, dm, text)); 92 num = 0; 93 } else { 94 g.drawLine(x2, y2, x5, y5); 95 list.add(new Shape(x2, y2, x5, y5, width, color, type, i, dm, text)); 96 x5 = x2; 97 y5 = y2; 98 } 99 } else { 100 Shape s = new Shape(x1, y1, x2, y2, width, color, type, i, dm, text); 101 s.draw(g); 102 list.add(s); 103 } 104 } 105 106 public void mouseDragged(MouseEvent e) { 107 if (type.equals("Pencil")) { 108 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 109 y2 = e.getY() + 183; 110 if (y2 < 183) 111 y2 = 183; 112 Shape s = new Shape(x1, y1, x2, y2, width, color, type, i, dm, text); 113 s.draw(g); 114 list.add(s); 115 x1 = x2; 116 y1 = y2; 117 } else if (type.equals("Erase")) { 118 x2 = e.getX() + 7; 119 y2 = e.getY() + 183; 120 if (y2 < 183) 121 y2 = 183; 122 Shape s = new Shape(x1, y1, x2, y2, width, Color.WHITE, type, i, dm, text); 123 s.draw(g); 124 list.add(s); 125 x1 = x2; 126 y1 = y2; 127 } else if (type.equals("喷枪")) // 难点 128 { 129 Random rand = new Random();// 实例化一个随机数类的对象 130 int size = rand.nextInt(50);// 随机决定要画的点数 131 x2 = e.getX() + 7; 132 y2 = e.getY() + 183; 133 for (int j = 0; j < size; j++) { 134 // 在0-7之间可以取50次 135 int x = rand.nextInt(10); 136 int y = rand.nextInt(10); 137 // 不断改变（x1,y1）的坐标值，实现在(x1,y1)的周围画点 138 Shape s = new Shape(x2 + x, y2 + y, x2 + x, y2 + y, width, color, type, i, dm, text); 139 s.draw(g); 140 list.add(s); 141 x1 = x2; 142 y1 = y2; 143 } 144 } 145 }
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
1 public class Shape { 2 3 private int x1, y1, x2, y2, width; 4 private Color color; 5 private String type; 6 private ImageIcon i; 7 private DrawMain dm; 8 private JTextField text; 9 10 public Shape(int x1, int y1, int x2, int y2, int width, Color color, String type, ImageIcon i, DrawMain dm, 11 JTextField text) { 12 this.x1 = x1; 13 this.y1 = y1; 14 this.x2 = x2; 15 this.y2 = y2; 16 this.width = width; 17 this.color = color; 18 this.type = type; 19 this.i = i; 20 this.dm = dm; 21 this.text = text; 22 } 23 24 25 public void draw(Graphics2D g) { 26 g.setColor(color); 27 g.setStroke(new BasicStroke(width)); 28 if (type.equals("Line") || type.equals("Pencil") || type.equals("iso_Tri") || type.equals("Polygon") 29 || type.equals("Erase") || type.equals("喷枪")) { 30 g.drawLine(x1, y1, x2, y2); 31 } else if (type.equals("Oval")) { 32 g.fillOval(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x2 - x1), Math.abs(y2 - y1)); 33 } else if (type.equals("Rect")) { 34 g.drawRect(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x2 - x1), Math.abs(y2 - y1)); 35 } else if (type.equals("RoundRect")) { 36 g.drawRoundRect(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x2 - x1), Math.abs(y2 - y1), 37 Math.abs(x2 - x1) / 3, Math.abs(y2 - y1) / 3); 38 } else if (type.equals("fill3DRect")) { 39 g.fill3DRect(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x2 - x1), Math.abs(y2 - y1), true); 40 } else if (type.equals("fillArc")) { 41 double r = ((x2 - x1) * (x2 - x1) + y1 * y1) / (2 * y1); 42 double m = Math.asin((double) (x2 - x1) / r); 43 g.fillArc(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x2 - x1), (int) r, 0, (int) (m * 180 / Math.PI)); 44 } else if (type.equals("Image")) { 45 g.drawImage(i.getImage(), Math.min(x1, x2), Math.min(y1, y2), Math.abs(x2 - x1), Math.abs(y2 - y1), dm); 46 } else if (type.equals("Text")) { 47 g.drawString(text.getText(), x1, y1); 48 } 49 } 50 51 }
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。