Android系列之手机多点触摸画圆

1、先写个实体类,代表圆

 public class MyCircle {
     public float x;
     public float y;
     public int r=100;
     public int pointId;
     int red;
     int green;
     int blue;
     Random random=new Random();

     public MyCircle(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.setStyle(Paint.Style.STROKE);
         paint.setColor(Color.rgb(red,green,blue));
         canvas.drawCircle(x,y,r,paint);
     }
 }

2、然后我们自己再写个java类，继承View  代表显示的界面

 public class MyView extends View {

     List lt=new ArrayList<>();



     public MyView(Context context) {
         super(context);
     }

     public MyView(Context context, @Nullable AttributeSet attrs) {
         super(context, attrs);
     }

     public MyView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
         super(context, attrs, defStyleAttr);
     }

     public MyView(Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {
         super(context, attrs, defStyleAttr, defStyleRes);
     }

     @Override
     protected void onDraw(Canvas canvas) {
         super.onDraw(canvas);
         Paint paint=new Paint();
         for (MyCircle myCircle : lt) {
             myCircle.drawSelf(canvas,paint);
         }

     }

     @Override
     public boolean onTouchEvent(MotionEvent event) {
         //获取手指的行为
         int action=event.getAction();
         int action_code=action&0xff;
         //手指的下标
         int pointIndex=action>>8;


         //获取手指的坐标
         float x=event.getX(pointIndex);
         float y=event.getY(pointIndex);



         //获取手指的名字的ID
         int pointId=event.getPointerId(pointIndex);
         if(action_code>=5){
             action_code-=5;
         }

         switch (action_code) {
             case MotionEvent.ACTION_DOWN:
                 //实例化园
                 MyCircle myCircle=new MyCircle(x,y,pointId);
                 //将园添加到集合中
                 lt.add(myCircle);
                 break;
             case MotionEvent.ACTION_UP:
                 lt.remove(get(pointId));
                 break;
             case MotionEvent.ACTION_MOVE:
                 for (int i = 0; i
                     int id=event.getPointerId(i);
                     get(id).x=event.getX(i);
                     get(id).y=event.getY(i);
                 }
                 break;
         }

         //重新调用onDraw 重绘
         invalidate();
         return true;
     }

     public MyCircle get(int pointId){
         for (MyCircle myCircle : lt) {
             if(myCircle.pointId==pointId){
                 return myCircle;
             }
         }
         return null;
     }


 }

最后我们在MainaActivity中改一句代码就可以了

 setContentView(new MyView(this));