近期公司項目告一段落，閑來無事，看到山東中國移動客戶端有個轉(zhuǎn)盤動畫挺酷的。于是試著實現(xiàn)一下，看似簡單，可在coding時卻發(fā)現(xiàn)不少坑，填坑的同時還順便復(fù)習(xí)了一下高中數(shù)學(xué)知識（三角函數(shù)），收獲不小。

Demo & 效果圖：

轉(zhuǎn)盤旋轉(zhuǎn)效果圖

1、首先初始化6個UIImageView

1）分析imgView的中心點位置

imgView的中心點位置

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）代碼

- (void)customUI {
    CGFloat centerX = CGRectGetWidth(self.frame) * 0.5f;
    CGFloat centerY = centerX;
    _centerPoint = CGPointMake(centerX, centerY);//中心點
    _blueView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];//藍色view
    _blueView.center = _centerPoint;
    _blueView.backgroundColor = [UIColor blueColor];
    [self addSubview:_blueView];
    UIView *redView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 50, 50)];//紅色view
    redView.backgroundColor = [UIColor redColor];
    [_blueView addSubview:redView];
    
    _deltaAngle = M_PI / 3.0f;//6個imgView的間隔角度
    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的距離
    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、轉(zhuǎn)起來

1）計算任意點相對于原點(O)及x軸的夾角?

A點相對于原點及x軸角度

以點A為例:

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); ?。。∽⒁?，此處有坑

坑在哪？cos(x)和sin(x)的周期是2π，所以必定在求arccos(x)時一個值對應(yīng)兩個角度，此時需要判斷點是在哪個象限（對于cos函數(shù)來說，要判斷點在第一、二象限還是在第三、四象限，如果是sin函數(shù)，則應(yīng)該判斷點是第二、三象限還是在第一、四象限）再進行計算。

下面是以cos函數(shù)分析:
如圖003，點C和點D，C在第二象限，D在第三象限，它們對應(yīng)的值相同但對應(yīng)的角度不同。
如果是C點，則CGFloat curentPointAngle = acos((currentPoint.x - _centerPoint.x) / currentPointRadius);
如果是D點，則curentPointAngle = (π - curentPointAngle) + π = 2 * π - curentPointAngle;

003

另外一個坑?。?！

不要嘗試用tan函數(shù)計算點相對于原點及x軸的夾角！

不要嘗試用tan函數(shù)計算點相對于原點及x軸的夾角??！

不要嘗試用tan函數(shù)計算點相對于原點及x軸的夾角！??！

因為tan函數(shù)在[0,2π]區(qū)間有2個周期，用的話會有出現(xiàn)各種bug！

2）計算變化的角度 Δ

以1）方法計算當(dāng)前點的角度curentPointAngle
上一個點的角度lastAngle
則變化角度CGFloat angle = lastAngle - curentPointAngle;

3）改變6個imgView中心點位置

    _lastImgViewAngle = fmod(_lastImgViewAngle + angle, 2 * M_PI);//對當(dāng)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）旋轉(zhuǎn)邏輯代碼

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

    UITouch *touch = [touches anyObject];
    CGPoint point = [touch locationInView:self];
    //計算上一個點相對于x軸的角度
    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<UITouch *> *)touches withEvent:(UIEvent *)event {

    UITouch *touch = [touches anyObject];
    CGPoint currentPoint = [touch locationInView:self];
    
    //1.計算當(dāng)前點相對于x軸的角度
    CGFloat currentPointRadius = sqrt(pow(currentPoint.y - _centerPoint.y, 2) + pow(currentPoint.x - _centerPoint.x, 2));
    if (currentPointRadius == 0) {//當(dāng)點在中心點時，被除數(shù)不能為0
        return;
    }
    CGFloat curentPointAngle = acos((currentPoint.x - _centerPoint.x) / currentPointRadius);
    if (currentPoint.y > _centerPoint.y) {
        curentPointAngle = 2 * M_PI - curentPointAngle;
    }
    //2.變化的角度
    CGFloat angle = _lastPointAngle - curentPointAngle;
    
    _blueView.transform = CGAffineTransformRotate(_blueView.transform, angle);
    
    _lastImgViewAngle = fmod(_lastImgViewAngle + angle, 2 * M_PI);//對當(dāng)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;
}

最后，推薦一個同事@shelin分享的實用小工具，iOS-Images-Extractor，能快速獲得iOS *.ipa包中的圖片（包括Assets.car）。