之前在知乎看到过一个网易云音乐听歌识曲界面的自定义View，实现的是一个带有水波纹扩散效果的控件，实现原理是ObjectAnimator，效果如下。

下面贴一下代码：

public class SunmiWaveView extends View {
    //圆圈个数
    int mCircleCount = 6;
    //圆圈之间的间隔
    int mInterval = 500;

    //每个圆圈的动画周期
    int mDuration = 3000;
    //透明度初始值
    int mStartAlpha = 105;
    int mEndAlpha = 0;

    //半径初始值
    int mStartRadius = 0;
    int mEndRadius = 150;
    private float radio = 0.75f;

    //动画开始时间
    long mAnimaStartTime;
    boolean isRunning;

    Interpolator mInterpolator = new LinearOutSlowInInterpolator();
    Circle[] mCircles;
    private Paint mPaint;

    public SunmiWaveView(Context context) {
        super(context);
        initCircles();
        initPaint();
    }

    public SunmiWaveView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initCircles();
        initPaint();
    }


    private void initCircles() {
        mCircles = new Circle[mCircleCount];
        for (int i = 0; i < mCircles.length; i++) {
            mCircles[i] = new Circle();
        }
    }

    private void initPaint() {
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setStyle(Paint.Style.FILL);
        mPaint.setColor(Color.RED);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        mEndRadius = (int) (Math.min(w, h) * radio / 2f);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        if (mAnimaStartTime == 0 || !isRunning)
            return;
        long pastTime = System.currentTimeMillis() - mAnimaStartTime;
        for (int i = 0; i < mCircleCount; i++) {
            int delay = i * mInterval;
            long pastTimeTrue = pastTime - delay;
            long timeInDuration = pastTimeTrue < 0 ? 0 : pastTimeTrue % mDuration;
            float percent = timeInDuration * 1f / mDuration;
            float percentWithInterpolate = mInterpolator.getInterpolation(percent);
            mCircles[i].radius = mStartRadius + (mEndRadius - mStartRadius) * percentWithInterpolate;
            mCircles[i].alpha = mStartAlpha + (int) ((mEndAlpha - mStartAlpha) * percentWithInterpolate);
            mPaint.setAlpha(mCircles[i].alpha);
            canvas.drawCircle(getWidth() / 2, getHeight() / 2, mCircles[i].radius, mPaint);
//            System.out.println("circle" + i + ": " + mCircles[i]);
        }
        postInvalidateDelayed(10);
    }

    public void start() {
        isRunning = true;
        mAnimaStartTime = System.currentTimeMillis();
        invalidate();
    }

    public void stop() {
        isRunning = false;
        for (Circle circle : mCircles) {
            circle.reset();
        }
    }

    public void setColor(int color) {
        mPaint.setColor(color);
    }

    public static class Circle {
        public int alpha;
        public float radius;

        public void reset() {
            alpha = 0;
            radius = 0;
        }

        @Override
        public String toString() {
            return "alpha: " + alpha + "  radius: " + radius;
        }

    }