Circlelayout 模拟一个时钟

##UICollectionViewLayout写一个Layout继承自UICollectionViewLayout，实现以下方法：//返回cell的Layout属性- (nullable UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath;//返回SupplementaryView的Layout属性（HeaderView、FooterView）- (nullable UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath;//返回DecorationView的Layout属性- (nullable UICollectionViewLayoutAttributes *)layoutAttributesForDecorationViewOfKind:(NSString*)elementKind atIndexPath:(NSIndexPath *)indexPath;实现prepareLayout方法，完成布局。在prepareLayout方法中调用[super prepareLayout];-(void)prepareLayout{    [super prepareLayout];    [self.attrsArr removeAllObjects];    //注册Decoration class    [self registerClass:[DecorationView class] forDecorationViewOfKind:@"DecorationView"];//注册Decoration View    }    layoutAttributesForElementsInRect方法中添加需要布局的所有Elements的Attributes    -(NSArray*)layoutAttributesForElementsInRect:(CGRect)rect{    NSInteger  count=[self.collectionView numberOfItemsInSection:0];    //添加DecorationView的LayoutAttributes    [self.attrsArr addObject:[self layoutAttributesForDecorationViewOfKind:@"DecorationView" atIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]]];    for (int i=0; i, <#CGFloat ty#>):只能变化一次，因为这种方式的变化始终是以最原始的状态值进行变化的，所以只能变化一次

UIButton *head = (UIButton *) [self.view viewWithTag:10];

head.transform = CGAffineTransformMakeTranslation(0,-10);

(2)CGAffineTransformTranslate(CGAffineTransform t, <#CGFloat tx#>, <#CGFloat ty#>):能够多次变化，每次变化都是以上一次的状态（CGAffineTransform t）进行的变化，所以可以多次变化

head.transform = CGAffineTransformTranslate(head.transform, 0, -10);

（3） CGAffineTransformIdentity:清空所有的设置的transform(一般和动画配合使用，只能使用于transfofrm设置的画面)

UIButton *head = (UIButton *) [self.view viewWithTag:10];

head.transform = CGAffineTransformIdentity;

（4）CGAffineTransformMakeScale( CGFloat  sx,  CGFloat  sy) （缩放:设置缩放比例）仅通过设置缩放比例就可实现视图扑面而来和缩进频幕的效果。

UIButton *head = [self.view viewWithTag:10];

head.transform = CGAffineTransformScale(head.transform,1.5,1.5);

（5） CGAffineTransformMakeRotation( CGFloat  angle) （旋转:设置旋转角度）

UIButton *head =  [self.view viewWithTag:10];

head.transform = CGAffineTransformMakeRotation(M_PI_2);

###实现UIView绕固定点旋转

定义方法：

CGAffineTransform  GetCGAffineTransformRotateAroundPoint(UIView *view,float centerX, float centerY ,float x ,float y ,float angle){

//centerX ,centerY 为当前View的中心点

x = x - centerX;

y = y - centerY;

CGAffineTransform  trans = CGAffineTransformTranslate(view.transform,x, y);

trans = CGAffineTransformRotate(trans,angle);

trans = CGAffineTransformTranslate(trans,-x, -y);

return trans;

}

使用如下：

float centerSecondX = self.secondHand.bounds.size.width/2;

float centerSecondY = self.secondHand.bounds.size.height/2;

float xSecond = self.secondHand.bounds.size.width/2;

float ySecond = self.secondHand.bounds.size.height;

CGAffineTransform transSecond = GetCGAffineTransformRotateAroundPoint(self.secondHand,centerSecondX,centerSecondY ,xSecond,ySecond,1*second/30.0*M_PI);

self.secondHand.transform = transSecond;

效果：