多点触摸画圆

多点触摸

安卓多点触摸画圆，手指抬起圆消失

先写一个圆的实体类

import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;

import java.util.Random;

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);
    }

}

再来一个类，继承View 重写它的四个方法

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

import java.util.ArrayList;
import java.util.List;

public class MyView extends View {

    List circles=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 (Circle circle : circles) {
            circle.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Index
        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ID
        int pointId=event.getPointerId(pointIndex);

        if(action_code>=5){
            action_code-=5;
        }

        switch (action_code) {
            //case 5:
            case MotionEvent.ACTION_DOWN:
                //实例化圆
                Circle circle=new Circle(x,y,pointId);
                //将圆添加到集合中
                circles.add(circle);
                break;
            case MotionEvent.ACTION_UP:
                circles.remove(get(pointId));
                break;
            case MotionEvent.ACTION_MOVE:
                for (int i = 0; i 

再去使用这个类就OK了

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new MyView(this));
    }
}