简易画板主要使用JFrame，JPanel，JLabel等，还要添加相应的监听器。
首先新建主类。
JFrame是一个容器，允许程序员把其他组件添加到它里面，把它们组织起来，并把它们呈现给用户。
public static void main(String[] args) {
DrawUI ui = new DrawUI();
ui.initDrawUI();
}
public void initDrawUI()
{
this.setTitle("画板");
this.setSize(600,500);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setVisible(ture);
}
}
将整个窗口分为西边，南边和中间三面，西边放工具，南边放颜色挑选，中间放置画板。所以整个窗口需要BorderLayout来分割窗口。
BorderLayout一个布置容器的边框布局，它可以对容器组件进行安排，并调整其大小，使其符合下列五个区域：北、南、东、西、中。每个区域最多只能包含一个组件，并通过相应的常量进行标识：NORTH、SOUTH、EAST、WEST、CENTER。当使用边框布局将一个组件添加到容器中时，要使用这五个常量之一。
//添加BorderLayout方法分割窗口：
BorderLayout layout = new BorderLayout();
this.setLayout(layout);
//分别在三面添加JPanel类，划分大小，并分别设置西边南边和中间的背景颜色。
JPanel left = new JPanel();
left.setPreferredSize(new Dimension(80,1));
left.setBackground(new Color(235,235,235));
JPanel center = new JPanel();
center.setBackground(Color.GRAY);
JPanel foot = new JPanel();
foot.setPreferredSize(new Dimension(1,80));
foot.setBackground(new Color(235,235,235));
//添加到窗口上
this.add(left,BorderLayout.WEST);
this.add(center,BorderLayout.CENTER);
this.add(foot,BorderLayout.SOUTH);
//在left添加工具按钮，并添加触碰，按下等的动作变化（这里需要用到for函数）。
//由于是单选按钮，则需要填加到group中。
ButtonGroup group = new ButtonGroup();
String[] commands = {"0","1","eraser","3","4","5","pencil","7","喷枪","9","line","11",
"rect","13","oval","15"
};
for(int i=0;i<16;i++)
{
JRadioButton radio = new JRadioButton();
ImageIcon lineIcon = new ImageIcon("imgs/draw"+i+".jpg");
radio.setIcon(lineIcon);
ImageIcon lineIcon1 = new ImageIcon("imgs/draw"+i+"-1.jpg");
radio.setRolloverIcon(lineIcon1);
ImageIcon lineIcon2 = new ImageIcon("imgs/draw"+i+"-2.jpg");
radio.setPressedIcon(lineIcon2);
ImageIcon lineIcon3 = new ImageIcon("imgs/draw"+i+"-3.jpg");
radio.setSelectedIcon(lineIcon3);
radio.setActionCommand(commands[i]);
group.add(radio);
left.add(radio);
}
//设置默认选择为pencil
if(i==6)
{
radio.setSelected(true);
}
//为center添加画板。
//JPanel 是一般轻量级容器。可以无限重叠自身。
JPanel drawPanel= new MyPanel();
drawPanel.setBackground(Color.WHITE);
drawPanel.setPreferredSize(new Dimension(400,300));
Graphics g = drawPanel.getGraphics();
//为工具添加鼠标监听器,将group和画板传入监听器，由此在选择group时
//对Graphics进行操作。
DrawListener dlis = new DrawListener(g,group);
drawPanel.addMouseListener(dlis);
drawPanel.addMouseMotionListener(dlis);
//新建DrawListener类
public class DrawListener implements MouseListener,MouseMotionListener{
private int x1,x2,y1,y2;
private String type="line";
private Graphics g;
private ButtonGroup group;
public DrawListener(Graphics g,ButtonGroup group)
{
this.g = g;
this.group = group;
}
}
//实现相应函数。
public void mousePressed(MouseEvent e)
{
// 鼠标按下的时候需要知道要绘制的形状是什么
javax.swing.ButtonModel bm = group.getSelection();
String command=bm.getActionCommand();
type=command;
g = drawPanel.getGraphics();
c = clis.color;
x1=e.getX();
y1=e.getY();
}
public void mouseReleased(MouseEvent e)
{
x2=e.getX();
y2=e.getY();
if(type.equals("line"))
{
g.drawLine(x1,y1,x2,y2);
}
else if(type.equals("rect"))
{
int minX = x1<x2?x1:x2;
int minY = y1<y2?y1:y2;
int width = x1<x2?x2-x1:x1-x2;
int height = y1<y2?y2-y1:y1-y2;
g.drawRect(minX, minY, width, height );
}
else if(type.equals("oval"))
{
int minX = Math.min(x1, x2);
int minY = Math.min(y1, y2);
int width = Math.abs(x2-x1);
int height = Math.abs(y2-y1);
g.drawOval(minX, minY, width, height );
}
else if(type.equals("eraser"))
{
int lx = e.getX();
int ly = e.getY();
int width = 10;
int height = 10;
g.setColor(Color.WHITE);
g.fillRect(lx, ly, width, height);
x1 = lx;
y1 = ly;
g.setColor(Color.BLACK);
}
else if (type.equals("喷枪"))
{
int x1 = e.getX();
int y1 = e.getY();
for(int i=0;i<100;i++)
{
int x2 = 15- (int) (Math.random()*30);
int y2 = 15- (int) (Math.random()*30);
g.drawLine(x1+x2, y1+y2, x1+x2, y1+y2);
}
}
}
public void mouseDragged(MouseEvent e) {
if(type.equals("pencil"))
{
int x3 = e.getX();
int y3 = e.getY();
g.drawLine(x1, y1, x3, y3);
x1 = x3;
y1 = y3;
}
else if(type.equals("eraser"))
{
int lx = e.getX();
int ly = e.getY();
int width = 10;
int height = 10;
g.setColor(Color.WHITE);
g.fillRect(lx, ly, width, height);
x1 = lx;
y1 = ly;
g.setColor(Color.BLACK);
}
else if (type.equals("喷枪"))
{
int x1 = e.getX();
int y1 = e.getY();
for(int i=1;i<50;i++)
{
int x2 = 15- (int) (Math.random()*30);
int y2 = 15- (int) (Math.random()*30);
g.drawLine(x1+x2, y1+y2, x1+x2, y2+y1);
}
}
}
public void mouseEntered(MouseEvent e)
{
}
public void mouseExited(MouseEvent e)
{
}
public void mouseClicked(MouseEvent e)
{
}
@Override
public void mouseMoved(MouseEvent e) {
// TODO Auto-generated method stub
}
保存绘画数据，且绘画始终在画板上。
将DrawUI中的drawPanel传入DrawListener中，则改为：
DrawListener dlis = new DrawListener(drawPanel,group);
DrawListener的构造函数更改：
public DrawListener(JPanel drawPanel,ButtonGroup group)
{
this.drawPanel = drawPanel;
this.group = group;
}
添加private JPanel drawPanel;
添加数组，存储数据：
定义一个shape类，然后让类Line继承，这样就可以将line的对象存储到数组中
public abstract class Shape {
int x1,y1,x2,y2;
Color color;
public abstract void draw(Graphics g);
}
public class Line extends Shape{
int x1,y1,x2,y2;
Color color;
Graphics group;
public Line(int x1,int y1,int x2,int y2,Color color)
{
this.x1 = x1;
this.x2 = x2;
this.y1 = y1;
this.y2 = y2;
this.color = color;
}
@Override
public void draw(Graphics g) {
g.setColor(this.color);
g.drawLine(x1, y1, x2, y2);
}
}
类似Line类可以写出相应的Oval类，Rect类等。
在DrawListener中的绘画直线的函数就更改为：
Line line = new Line(x1,y1,x2,y2,color.BLACK);
line.draw(g);
用MyPanel类重写JPanel类中的paint方法，使得每次更改窗口都会重绘存储在数组中的数据。
class MyPanel extends JPanel
{
@Override
public void paint(Graphics g) {
super.paint(g);
for(int i=0;i<DrawListener.shapeList.size();i++)
{
Shape s = DrawListener.shapeList.get(i);
s.draw(g);
}
}
}
JPanel drawPanel = new JPanel();更改为JPanel drawPanel = new MyPanel();
DrawListener中添加：
public static ArrayList<Shape> shapeList = new ArrayList<Shape>();
绘制line中添加
shapeList.add(line);
为颜色按钮添加ColorListener监听器
public class ColorListener extends MouseAdapter implements ActionListener{
@Override
public void mouseReleased(MouseEvent e) {
super.mouseReleased(e);
JLabel label = (JLabel) e.getSource();
color = label.getBackground();
}
Color color;
@Override
public void actionPerformed(ActionEvent e) {
color = JColorChooser.showDialog(null, "请选择颜色", Color.RED);
}
}
在DrawUI中实现
在foot中添加颜色按钮
for(int i=0;i<colors.length;i++){
JLabel label = new JLabel();
label.setPreferredSize(new Dimension(34,29));
label.setBackground(colors[i]);
//前景色是否透明
label.setOpaque(true);
foot.add(label);
label.addMouseListener(clis);
}
颜色监听器放在工具监听器的前面，将颜色监听器的对象传入工具监听器中，实现对绘画的改色。
DrawListener dlis = new DrawListener(drawPanel,group,clis);
相应的构造函数需要改变。
public DrawListener(JPanel drawPanel,ButtonGroup group,ColorListener clis)
{
this.drawPanel = drawPanel;
this.group = group;
this.clis = clis;
}
在foot中添加颜色选择器（传入照片color.png)
JButton btn = new JButton();
ImageIcon icon = new ImageIcon("color.png");
btn.setIcon(icon);
btn.setPreferredSize(new Dimension(34,29));
foot.add(btn);
btn.addActionListener(clis);