Android 幸运转盘实现逻辑

一、前言

幸运转盘在很多app中都有，也有很多现实的例子，不过这个难度并不是如何让转盘转起来，真正的难度是如何统一个方向转动，且转到指定的目标区域（中奖概率从来不是随机的），当然还不能太假，需要有一定的位置偏移。

效果预览

二、逻辑实现

2.1 平分区域

由于圆周是360度，品分每个站preDegree，那么起点和终点

但是为了让X轴初始化时对准第一个区域的中心，我们做一下小偏移，逆时针旋转一下

//圆点起始角度 ，可以理解为index=0的起始角度，我们以index=0位参考点
float zeroStartDegree = 0 + -perDegree / 2;
float endStartDegree = 0 + perDegree / 2;

那么每个区域的起始角度如下

float startDegree = i* perDegree  - perDegree / 2;
float endDegree = i * perDegree + perDegree / 2 ;

2.2 画弧

很简单，不需要计算每个分区的大小，因为平分的是同一个大圆，因此Rect是大圆的范围，但也要记住 ,弧的起始角+绘制角度不能大于等于360，最大貌似是359.9998399

canvas.drawArc(rectF, startDegree, endDegree - startDegree, true, mDrawerPaint);

2.3 文字绘制

由于Canvas.drawText不能设置角度，那么意味着不能直接绘制，需要做一定的角度转换，要么旋转Canvas坐标，要们旋转Path，这次我们选后者吧。

使用Path的原因是，他不仅具备矢量性质（不失真），而且还能转动文字的方向和从有到左绘制。

           //计算出中心角度 float centerRadius = (float) Math.toRadians((startDegree + endDegree)/2F);float measuredTextWidth = mDrawerPaint.measureText(item.text);float measuredTextHeight = getTextHeight(mDrawerPaint,item.text);float innerRadius = maxRadius - 2* measuredTextHeight;float cx = (float) ((innerRadius - measuredTextHeight)   * Math.cos(centerRadius));float cy = (float) ((innerRadius - measuredTextHeight)  * Math.sin(centerRadius));double degreeOffset = Math.asin((measuredTextWidth/2F)/innerRadius);float startX= (float) (innerRadius * Math.cos(centerRadius - degreeOffset));float startY = (float) (innerRadius * Math.sin(centerRadius - degreeOffset));float endX= (float) ((innerRadius) * Math.cos(centerRadius + degreeOffset));float endY = (float) ((innerRadius) * Math.sin(centerRadius + degreeOffset));path.reset();path.moveTo(startX,startY);path.lineTo(endX,endY);//这里使用Path的原因是文本角度无法设置canvas.drawTextOnPath(item.text,path,0,0,mDrawerPaint);

2.4 核心逻辑

老板不会让中奖率随机的，万一你中大奖了，老板还得出钱或者花部门经费，因此，必须指定中奖物品，可以让你100%中奖，也能让你100%不中奖，要看老板心情，所以掘金的转盘你玩不玩都已经固定好你的胜率了。

计算出目标物品与初始角度的，注意时初始角度，而不是转过后的角度算起，为什么呢？原因是你按转过的角度计算复杂度就会提升，而从起始点计算，按照圆的三角函数定理，转一圈就能绕过你转动的角度，也就是 rotateDegree 最终会大于你当前的所停留的角度，如果你在30度，那么要转到20度的位置，肯定不会倒转需要 360 + 20,而360 +20大于30，所以，莫有必要从当前角度计算。

//圆点起始角度 ，可以理解为index=0的起始角度，我们以index=0位参考点
float zeroStartDegree = 0 + -perDegree / 2;
float endStartDegree = 0 + perDegree / 2;
//从圆点计算，要旋转的角度
float targetDegree = (perDegree * (index - 1) + perDegree / 2);
float rotateDegree = zeroStartDegree - targetDegree;

算出来之后紧接着计算落点位置，这里需要随机一下，不然看着很假，样子还是要做的。

但是这里我们一气呵成：

【1】计算旋转速度，主要是防止逆时针旋转，其词转一下就到了，也不太真实，次数利用了三角函数定理

三角函数定理 n*360 + degree 和 degree三角函数值最终夹角是等价的

【2】旋转次数，这里我们用duration/speedTime，实际上还可以用圆周边长除以duration，也是可以的，当然也要加一定的倍数。

【3】计算出随机落点位置，不能骑线，也不能超过指定区域

        //防止逆时针旋转 （三角函数定理  n*360 + degree 和 degree最终夹角是等价的 ）while (rotateDegree < offsetDegree) {rotateDegree += 360;}if (speedTime == 0) {speedTime = 100L;}long count = duration / speedTime - 1;  //计算额外旋转圈数while (count >= 0) {rotateDegree += 360;  //三角函数定理  n*360 + degree 和 degree最终夹角是等价的count--; //算出转多少圈}float targetStartDegree = rotateDegree - perDegree / 2;float targetEndDegree = rotateDegree + perDegree / 2;float currentOffsetDegree = offsetDegree;// float targetOffsetDegree  = (targetStartDegree +  targetEndDegree)/2 ;//让指针指向有一定的随机性float targetOffsetDegree = (float) (targetStartDegree + (targetEndDegree - targetStartDegree) * Math.random());

2.5 全部代码

public class LuckWheelView extends View {Path path  = new Path();private final DisplayMetrics mDM;private TextPaint mArcPaint;private TextPaint mDrawerPaint;private int maxRadius;private float perDegree;private long duration = 5000L;private List<Item> items = new ArrayList<>();private RectF rectF = new RectF();private float offsetDegree = 0;private TimeInterpolator timeInterpolator = new AccelerateDecelerateInterpolator();private long speedTime = 1000L; //旋转一圈需要多少时间private ValueAnimator animator = null;public LuckWheelView(Context context) {this(context, null);}public LuckWheelView(Context context, AttributeSet attrs) {this(context, attrs, 0);}public LuckWheelView(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);mDM = getResources().getDisplayMetrics();initPaint();}public void setRotateIndex(int index) {if (items == null || items.size() <= index) {return;}//圆点起始角度 ，可以理解为index=0的起始角度，我们以index=0位参考点float zeroStartDegree = 0 + -perDegree / 2;float endStartDegree = 0 + perDegree / 2;//从圆点计算，要旋转的角度float targetDegree = (perDegree * (index - 1) + perDegree / 2);float rotateDegree = zeroStartDegree - targetDegree;//防止逆时针旋转 （三角函数定理  n*360 + degree 和 degree最终夹角是等价的 ）while (rotateDegree < offsetDegree) {rotateDegree += 360;}if (speedTime == 0) {speedTime = 100L;}long count = duration / speedTime - 1;  //计算额外旋转圈数while (count >= 0) {rotateDegree += 360;  //三角函数定理  n*360 + degree 和 degree最终夹角是等价的count--;}float targetStartDegree = rotateDegree - perDegree / 2;float targetEndDegree = rotateDegree + perDegree / 2;float currentOffsetDegree = offsetDegree;// float targetOffsetDegree  = (targetStartDegree +  targetEndDegree)/2 ;//让指针指向有一定的随机性float targetOffsetDegree = (float) (targetStartDegree + (targetEndDegree - targetStartDegree) * Math.random());if (animator != null) {animator.cancel();}
//起点肯定要从当前角度算起，不然会闪一下回到原点animator = ValueAnimator.ofFloat(currentOffsetDegree, targetOffsetDegree).setDuration(duration);animator.setInterpolator(timeInterpolator);animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {@Overridepublic void onAnimationUpdate(ValueAnimator animation) {offsetDegree = (float) animation.getAnimatedValue();postInvalidate();}});animator.addListener(new AnimatorListenerAdapter() {@Overridepublic void onAnimationEnd(Animator animation) {super.onAnimationEnd(animation);offsetDegree = offsetDegree % 360;}});animator.start();}private void initPaint() {// 实例化画笔并打开抗锯齿mArcPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);mArcPaint.setAntiAlias(true);mArcPaint.setStyle(Paint.Style.STROKE);mArcPaint.setStrokeCap(Paint.Cap.ROUND);mDrawerPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);mDrawerPaint.setAntiAlias(true);mDrawerPaint.setStyle(Paint.Style.FILL);mDrawerPaint.setStrokeCap(Paint.Cap.ROUND);mDrawerPaint.setStrokeWidth(5);mDrawerPaint.setTextSize(spTopx(14));}private float spTopx(float dp) {return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, dp, getResources().getDisplayMetrics());}@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {super.onMeasure(widthMeasureSpec, heightMeasureSpec);int widthMode = MeasureSpec.getMode(widthMeasureSpec);int widthSize = MeasureSpec.getSize(widthMeasureSpec);if (widthMode != MeasureSpec.EXACTLY) {widthSize = mDM.widthPixels / 2;}int heightMode = MeasureSpec.getMode(heightMeasureSpec);int heightSize = MeasureSpec.getSize(heightMeasureSpec);if (heightMode != MeasureSpec.EXACTLY) {heightSize = widthSize / 2;}setMeasuredDimension(widthSize, heightSize);}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);int width = getWidth();int height = getHeight();if (width == 0 || height == 0 || items == null || items.size() <= 0) {perDegree = 0;return;}maxRadius = Math.min(width / 2, height / 2);rectF.left = -maxRadius;rectF.top = -maxRadius;rectF.right = maxRadius;rectF.bottom = maxRadius;int size = items.size();int saveCount = canvas.save();canvas.translate(width * 1F / 2, height * 1F / 2); //平移坐标轴到view中心点canvas.rotate(-90); //逆时针旋转坐标轴 90度perDegree = 360 * 1F / size;// rangeDegree = start ->end// rangeDegree.start = perDegree/2 + (i-1) * perDegree;// rangeDegree.end = perDegree/2 + (i) * perDegree;for (int i = 0; i < size; i++) {//由于我们让第一个区域的中心点对准x轴了，所以(i-1)意味着从y轴负方向顺时针转动float startDegree = perDegree * (i - 1) + perDegree / 2 + offsetDegree;float endDegree = i * perDegree + perDegree / 2 + offsetDegree;Item item = items.get(i);mDrawerPaint.setColor(item.color);
//            double startDegreeRandians = Math.toRadians(startDegree); //x1
//            float x = (float) (maxRadius * Math.cos(startDegreeRandians));
//            float y = (float) (maxRadius * Math.sin(startDegreeRandians));
//            canvas.drawLine(0,0,x,y,mDrawerPaint);float centerRadius = (float) Math.toRadians((startDegree + endDegree)/2F);float measuredTextWidth = mDrawerPaint.measureText(item.text);float measuredTextHeight = getTextHeight(mDrawerPaint,item.text);float innerRadius = maxRadius - 2* measuredTextHeight;float cx = (float) ((innerRadius - measuredTextHeight)   * Math.cos(centerRadius));float cy = (float) ((innerRadius - measuredTextHeight)  * Math.sin(centerRadius));double degreeOffset = Math.asin((measuredTextWidth/2F)/innerRadius);float startX= (float) (innerRadius * Math.cos(centerRadius - degreeOffset));float startY = (float) (innerRadius * Math.sin(centerRadius - degreeOffset));float endX= (float) ((innerRadius) * Math.cos(centerRadius + degreeOffset));float endY = (float) ((innerRadius) * Math.sin(centerRadius + degreeOffset));path.reset();path.moveTo(startX,startY);path.lineTo(endX,endY);//这里使用Path的原因是文本角度无法设置canvas.drawArc(rectF, startDegree, endDegree - startDegree, true, mDrawerPaint);mDrawerPaint.setColor(Color.WHITE);canvas.drawCircle(cx,cy,5,mDrawerPaint);canvas.drawTextOnPath(item.text,path,0,0,mDrawerPaint);}canvas.drawLine(0, 0, maxRadius / 2F, 0, mDrawerPaint);canvas.restoreToCount(saveCount);}Rect textBounds = new Rect();//真实宽度 + 笔画上下两侧间隙（符合文本绘制基线）private  int getTextHeight(Paint paint,String text) {paint.getTextBounds(text,0,text.length(),textBounds);return textBounds.height();}public void setItems(List<Item> items) {this.items.clear();this.items.addAll(items);invalidate();}public static class Item {Object tag;int color = Color.TRANSPARENT;String text;public Item(int color, String text) {this.color = color;this.text = text;}}}

2.6 使用方法

List<LuckWheelView.Item> items = new ArrayList<>();items.add(new LuckWheelView.Item(argb(random.nextFloat(),random.nextFloat(),random.nextFloat()), "金元宝"));items.add(new LuckWheelView.Item(argb(random.nextFloat(),random.nextFloat(),random.nextFloat()), "皮卡丘"));items.add(new LuckWheelView.Item(argb(random.nextFloat(),random.nextFloat(),random.nextFloat()), "1元红包"));items.add(new LuckWheelView.Item(argb(random.nextFloat(),random.nextFloat(),random.nextFloat()), "全球旅行"));items.add(new LuckWheelView.Item(argb(random.nextFloat(),random.nextFloat(),random.nextFloat()), "K歌会员卡"));items.add(new LuckWheelView.Item(argb(random.nextFloat(),random.nextFloat(),random.nextFloat()), "双肩包"));loopView.setItems(items);loopView.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {int index = (int) (Math.random() * items.size());Log.d("LuckWheelView", "setRotateIndex->" + items.get(index).text + ", index=" + index);loopView.setRotateIndex(index);}});