iOS 转盘动画效果实现

近期公司项目告一段落，闲来无事，看到山东中国移动客户端有个转盘动画挺酷的。于是试着实现一下，看似简单，可在coding时却发现不少坑，填坑的同时还顺便复习了一下高中数学知识（三角函数），收获不小。

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Demo & 效果图：

转盘旋转效果图

1、首先初始化6个UIImageView

1）分析imgView的中心点位置

imgView的中心点位置

Δx = _radius * sin(α);
Δy = _radius * cos(α);
所以，
imgView.center.x = centerX + _radius * sin(currentAngle);
imgView.center.y = centerY - _radius * cos(currentAngle);

2）代码

- (void)customUI {
    CGFloat centerX = CGRectGetWidth(self.frame) * 0.5f;
    CGFloat centerY = centerX;
    _centerPoint = CGPointMake(centerX, centerY);//中心点
    _blueView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];//蓝色view
    _blueView.center = _centerPoint;
    _blueView.backgroundColor = [UIColor blueColor];
    [self addSubview:_blueView];
    UIView *redView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 50, 50)];//红色view
    redView.backgroundColor = [UIColor redColor];
    [_blueView addSubview:redView];
    
    _deltaAngle = M_PI / 3.0f;//6个imgView的间隔角度
    CGFloat currentAngle = 0;
    CGFloat imgViewCenterX = 0;
    CGFloat imgViewCenterY = 0;
    CGFloat imgViewW = 80;
    CGFloat imgViewH =imgViewW;
    _radius = centerX - imgViewW * 0.5f;//imgView.center到self.center的距离
    for (int i = 0; i < 6; i++) {
        currentAngle = _deltaAngle * i;
        imgViewCenterX = centerX + _radius * sin(currentAngle);
        imgViewCenterY = centerY - _radius * cos(currentAngle);
        UIImageView *imgView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, imgViewW, imgViewH)];
        imgView.tag = kTag + i;
        imgView.center = CGPointMake(imgViewCenterX, imgViewCenterY);
        imgView.image = [UIImage imageNamed:[NSString stringWithFormat:@"circle%d", i]];
        [self addSubview:imgView];
    }
}

2、转起来

1）计算任意点相对于原点(O)及x轴的夹角⍺

A点相对于原点及x轴角度

以点A为例:

CGFloat currentPointRadius = sqrt(pow(currentPoint.y - _centerPoint.y, 2) + pow(currentPoint.x - _centerPoint.x, 2));

所以，⍺ = arccos((A.x - O.x) / OA)， CGFloat curentPointAngle = acos((currentPoint.x - _centerPoint.x) / currentPointRadius); ！！！注意，此处有坑

坑在哪？cos(x)和sin(x)的周期是2π，所以必定在求arccos(x)时一个值对应两个角度，此时需要判断点是在哪个象限（对于cos函数来说，要判断点在第一、二象限还是在第三、四象限，如果是sin函数，则应该判断点是第二、三象限还是在第一、四象限）再进行计算。

下面是以cos函数分析:
如图003，点C和点D，C在第二象限，D在第三象限，它们对应的值相同但对应的角度不同。
如果是C点，则CGFloat curentPointAngle = acos((currentPoint.x - _centerPoint.x) / currentPointRadius);
如果是D点，则curentPointAngle = (π - curentPointAngle) + π = 2 * π - curentPointAngle;

003

另外一个坑！！！

不要尝试用tan函数计算点相对于原点及x轴的夹角！

不要尝试用tan函数计算点相对于原点及x轴的夹角！！

不要尝试用tan函数计算点相对于原点及x轴的夹角！！！

因为tan函数在[0,2π]区间有2个周期，用的话会有出现各种bug！

2）计算变化的角度 Δ

以1）方法计算当前点的角度curentPointAngle
上一个点的角度lastAngle
则变化角度CGFloat angle = lastAngle - curentPointAngle;

3）改变6个imgView中心点位置

    _lastImgViewAngle = fmod(_lastImgViewAngle + angle, 2 * M_PI);//对当前角度取模
    CGFloat currentAngle = 0;
    CGFloat imgViewCenterX = 0;
    CGFloat imgViewCenterY = 0;
    for (int i = 0; i < 6; i++) {
        UIImageView *imgView = [self viewWithTag:kTag];
        currentAngle = _deltaAngle * i + _lastImgViewAngle;
        imgViewCenterX = _centerPoint.x + _radius * sin(currentAngle);
        imgViewCenterY = _centerPoint.x - _radius * cos(currentAngle);
        imgView = [self viewWithTag:kTag + i];
        imgView.center = CGPointMake(imgViewCenterX, imgViewCenterY);
    }

4）旋转逻辑代码

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    UITouch *touch = [touches anyObject];
    CGPoint point = [touch locationInView:self];
    //计算上一个点相对于x轴的角度
    CGFloat lastPointRadius = sqrt(pow(point.y - _centerPoint.y, 2) + pow(point.x - _centerPoint.x, 2));
    if (lastPointRadius == 0) {
        return;
    }
    _lastPointAngle = acos((point.x - _centerPoint.x) / lastPointRadius);
    if (point.y > _centerPoint.y) {
        _lastPointAngle = 2 * M_PI - _lastPointAngle;
    }
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {

    UITouch *touch = [touches anyObject];
    CGPoint currentPoint = [touch locationInView:self];
    
    //1.计算当前点相对于x轴的角度
    CGFloat currentPointRadius = sqrt(pow(currentPoint.y - _centerPoint.y, 2) + pow(currentPoint.x - _centerPoint.x, 2));
    if (currentPointRadius == 0) {//当点在中心点时，被除数不能为0
        return;
    }
    CGFloat curentPointAngle = acos((currentPoint.x - _centerPoint.x) / currentPointRadius);
    if (currentPoint.y > _centerPoint.y) {
        curentPointAngle = 2 * M_PI - curentPointAngle;
    }
    //2.变化的角度
    CGFloat angle = _lastPointAngle - curentPointAngle;
    
    _blueView.transform = CGAffineTransformRotate(_blueView.transform, angle);
    
    _lastImgViewAngle = fmod(_lastImgViewAngle + angle, 2 * M_PI);//对当前角度取模
    CGFloat currentAngle = 0;
    CGFloat imgViewCenterX = 0;
    CGFloat imgViewCenterY = 0;
    for (int i = 0; i < 6; i++) {
        UIImageView *imgView = [self viewWithTag:kTag];
        currentAngle = _deltaAngle * i + _lastImgViewAngle;
        imgViewCenterX = _centerPoint.x + _radius * sin(currentAngle);
        imgViewCenterY = _centerPoint.x - _radius * cos(currentAngle);
        imgView = [self viewWithTag:kTag + i];
        imgView.center = CGPointMake(imgViewCenterX, imgViewCenterY);
    }
    
    _lastPointAngle = curentPointAngle;
}

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最后，推荐一个同事@shelin分享的实用小工具，iOS-Images-Extractor，能快速获得iOS *.ipa包中的图片（包括Assets.car）。