安卓自定义view 波纹效果

package com.cy.zdyview;

import android.annotation.TargetApi;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.os.Build;
import android.util.AttributeSet;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.View;

import org.jetbrains.annotations.Nullable;

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

/**
 * Created by bower on 2018/7/6.
 */

public class MyView extends View {
    public MyView(Context context) {
        super(context);
        init();
    }

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

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

    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    public MyView(Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        init();
    }

    Paint mPaint=new Paint();
    Path mPath=new Path();
    int x1=0,x2=100,x3=200;
    private void init() {
        mPaint = new Paint();

        // 抗锯齿
        mPaint.setAntiAlias(true);
        // 防抖动
        mPaint.setDither(true);
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        // 画笔颜色
        mPaint.setColor(Color.RED);
        // 笔宽
        mPaint.setStrokeWidth(6);
        // 空心
        mPaint.setStyle(Paint.Style.FILL);

        mPaint.setAlpha((int)(255-x1*255/330));
        canvas.drawCircle(canvas.getWidth()/2,canvas.getHeight()/2,x1, mPaint);
        mPaint.setAlpha((int)(255-x2*255/330));
        canvas.drawCircle(canvas.getWidth()/2,canvas.getHeight()/2,x2, mPaint);
        mPaint.setAlpha((int)(255-x3*255/330));
        canvas.drawCircle(canvas.getWidth()/2,canvas.getHeight()/2,x3, mPaint);
        x1=x1+1;
        x2=x2+1;
        x3=x3+1;
        if(x1==330)
            x1=0;
        if(x2==330)
            x2=0;
        if(x3==330)
            x3=0;
        postInvalidateDelayed(13);

    }


}