android中实现在ImageView上随意画线涂鸦的方法

//代表ImageView上的一点
public class ViewPoint
{
　　float x;
　　float y;
}

//表示一条线
public class Line
{
　　ArrayList<ViewPoint> points = new ArrayList<ViewPoint>(); 
}

public class HandWritingImageView extends ImageView
{
　　private Paint paint;

　　//当前正在画的线
　　private Line current = new Line();
 //所有画过的线
　　private ArrayList<Line> lines = new ArrayList<Line>(); 
}

@Override
 public boolean onTouchEvent(MotionEvent event)
 { 
 //获取坐标
 clickX = event.getX();
 clickY = event.getY();
 
 if (event.getAction() == MotionEvent.ACTION_DOWN)
 {
  invalidate();
  
  return true;
 }
 else if (event.getAction() == MotionEvent.ACTION_MOVE) 
 {
  ViewPoint point = new ViewPoint();
  point.x = clickX;
  point.y = clickY;
  //在移动时添加所经过的点
  current.points.add(point);

  invalidate();
  return true;
 }
 else if (event.getAction() == MotionEvent.ACTION_UP) 
 { 
  //添加画过的线
  lines.add(current);
  current = new Line();
   
  invalidate();
 }
 
 return super.onTouchEvent(event);
 }

@Override 
 protected void onDraw(Canvas canvas) 
 { 
 super.onDraw(canvas);
 //画出之前所有的线
 for (int i = 0; i < lineData.lines.size(); i++)
 {
  drawLine(canvas, lines.get(i));
 }
  
 //画出当前的线
 drawLine(canvas, current);
 
 } 
 
 private void drawLine(Canvas canvas, Line line)
 {
 for (int i = 0; i < line.points.size() - 1; i++)
 {
  float x = line.points.get(i).x;
  float y = line.points.get(i).y;
  
  float nextX = line.points.get(i + 1).x;
  float nextY = line.points.get(i + 1).y;
  
  canvas.drawLine(x, y, nextX, nextY, paint);
 }
 }