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。