Android—检测手机多点触摸点数

演示效果如下：

//写一个实体类
public class Circle {
    public float x;
    public float y;
    public int r=100;
    public int pointId;
    int red;
    int green;
    int blue;
    Random random=new Random();
    public Circle(float x, float y, int pointId) {
        this.x = x;
        this.y = y;
        this.pointId = pointId;
        red=random.nextInt(255);
        green=random.nextInt(255);
        blue=random.nextInt(255);
    }
    public void drawSelf(Canvas canvas, Paint paint){
        paint.setColor(Color.rgb(red,green,blue));
        canvas.drawCircle(x,y,r,paint);
    }
}

/**
 * 1.多点触摸画圆
 * 2.抬起手移除圆
 * 3.圆可移动
 * 4.设置圆的颜色
 */
public class MyView extends View{
    List<Circle> circles=new ArrayL