1、Math.atan()与Math.atan2()的区别

angle = Math.atan(slope)
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slope斜率值为y/x，返回值angle为一个角度的弧度制，因为角度的周期性，此方法不能很好的反应角度,应使用Math.atan2替换。

angle = Math.atan2(y,x)
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x是临边边长，y是对边边长。

弧度转角度方法：

    弧度 = 角度 * Math.PI / 180;角度 = 弧度 * 180 / Math.PI;
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计算两点间连线的倾斜角：

Math.atan2()函数返回的是点(x,y)和原点(0,0)之间直线的倾斜角，计算任意两点的切斜角，应使用Math.atan2(y2-y1,x2-x1)。

2、PathMeasure结合ValueAnimator实现轨迹绘制效果

关键方法：

PathMeasure#getLength()：获取轨迹总长度

PathMeasure#getSegment(float startD, float stopD, Path dst, boolean startWithMoveTo)：startD、stopD分别是轨迹长度值，dst是保存到的片段路径。

public class CirclePathView extends View {private int mWidth;private int mHeight;private PathMeasure mPathMeasure;private float mLength;private Path mDst;private float animatedValue;private Paint mPaint;private Path mPath;public CirclePathView(Context context) {this(context,null);}public CirclePathView(Context context, @Nullable AttributeSet attrs) {this(context, attrs,0);}public CirclePathView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);initView();}@Overrideprotected void onSizeChanged(int w, int h, int oldw, int oldh) {super.onSizeChanged(w, h, oldw, oldh);mWidth = w;mHeight = h;mPath = new Path();mPath.addCircle(mWidth / 2,mHeight / 2,mWidth / 4,Path.Direction.CW);mPathMeasure = new PathMeasure();mPathMeasure.setPath(mPath,true);mLength = mPathMeasure.getLength();}private void initView() {mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);mPaint.setStyle(Paint.Style.STROKE);mPaint.setStrokeWidth(5);mPaint.setColor(Color.BLACK);mDst = new Path();ValueAnimator animator = ValueAnimator.ofFloat(1, 0);animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {@Overridepublic void onAnimationUpdate(ValueAnimator animation) {animatedValue = (float) animation.getAnimatedValue();invalidate();}});animator.setDuration(2000);animator.setRepeatCount(ValueAnimator.INFINITE);animator.start();}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);mDst.reset();mDst.lineTo(0,0);float stop = mLength * animatedValue;float start = (animatedValue - 0.5f > 0 ? (animatedValue - 0.5f) * 2 : 0f) * mLength;mPathMeasure.getSegment(start,stop,mDst,true);canvas.drawPath(mDst,mPaint);}
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轨迹效果也可使用DashPathEffect，通过控制实线的偏移量来实现。

3、点赞-飘心效果

• 获取一个间于min和max之间的随机值：

int randomNum = new Random().nextInt(max - min + 1) + min;
//int randomNum = new Random().nextInt(max) % (max - min + 1) + min; //好傻噢
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• AS打开工程报错ssl peer shut down incorrectly：gradle版本问题。
• GitHub飘心点赞项目：github.com/trc1993/And…

核心逻辑：确认红心起点、终点坐标（高度随机），创建2阶贝塞尔曲线，通过PathMeasure.getPosTan()和ValueAnimator，获取路径上每个点的坐标，再通过View#setTranslationX()和View#setTranslationY()移动红心。

    private void addFHeart(ImageView startLocationIv, Drawable floatDrawable) {int min = animMinWidth;int max = animMaxWidth;Random random = new Random();animWidth = random.nextInt(max - min + 1) + min;int min1 = animMinHeight;int max1 = animMaxHeight;Random random1 = new Random();animHeight = random1.nextInt(max1 - min1 + 1) + min1;final ImageView _floatIv = new ImageView(context);_floatIv.setImageDrawable(floatDrawable);RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(floatIconWidth, floatIconHeight);params.width = DisplayUtil.dip2px(context, floatIconWidth);params.height = DisplayUtil.dip2px(context, floatIconHeight);FRl.addView(_floatIv, params);int[] parentLocation = new int[2];FRl.getLocationInWindow(parentLocation);//得到起始图片的坐标（用于计算动画开始的坐标）int startLoc[] = new int[2];startLocationIv.getLocationInWindow(startLoc);//        三、正式开始计算动画开始/结束的坐标//起始点：图片起始点-父布局起始点+该图片的一半startX = startLoc[0] - parentLocation[0];startY = startLoc[1] - parentLocation[1];endX = startX;endY = startY - animHeight;firstControlX = startX - animWidth;firstControlY = startY - animHeight * 3 / 8;secondControlX = startX + animWidth;secondControlY = startY - animHeight * 5 / 8;Path path = new Path();path.moveTo(startX, startY);path.cubicTo(firstControlX, firstControlY, secondControlX, secondControlY, endX, endY);final PathMeasure mPathMeasure = new PathMeasure(path, false);//★★★属性动画实现（从0到贝塞尔曲线的长度之间进行插值计算，获取中间过程的距离值）AnimatorSet bouncer = new AnimatorSet();ValueAnimator valueAnimator = ValueAnimator.ofFloat(0, mPathMeasure.getLength());ObjectAnimator anim = ObjectAnimator.ofFloat(_floatIv, "alpha", 1f, 0.1f);// 匀速线性插值器bouncer.setInterpolator(new LinearInterpolator());valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {@Overridepublic void onAnimationUpdate(ValueAnimator animation) {// 当插值计算进行时，获取中间的每个值，// 这里这个值是中间过程中的曲线长度（下面根据这个值来得出中间点的坐标值）float value = (Float) animation.getAnimatedValue();Log.d("FloatHeartView", "value:" + value);// ★★★★★获取当前点坐标封装到mCurrentPosition// boolean getPosTan(float distance, float[] pos, float[] tan) ：// 传入一个距离distance(0<=distance<=getLength())，然后会计算当前距// 离的坐标点和切线，pos会自动填充上坐标，这个方法很重要。mPathMeasure.getPosTan(value, mCurrentPosition, null);//mCurrentPosition此时就是中间距离点的坐标值// 移动的图片（动画图片）的坐标设置为该中间点的坐标_floatIv.setTranslationX(mCurrentPosition[0]);_floatIv.setTranslationY(mCurrentPosition[1]);}});bouncer.play(valueAnimator).with(anim);bouncer.setDuration(animDuration);bouncer.start();bouncer.addListener(new Animator.AnimatorListener() {@Overridepublic void onAnimationStart(Animator animation) {}//当动画结束后：@Overridepublic void onAnimationEnd(Animator animation) {
//                // 把移动的图片imageview从父布局里移除FRl.removeView(_floatIv);}@Overridepublic void onAnimationCancel(Animator animation) {}@Overridepublic void onAnimationRepeat(Animator animation) {}});}
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4、点赞-数字滚动+1效果

juejin.im/post/5c2190…

5、支付宝、微信、银联支付

juejin.im/post/596d97…