AsyncDisplayKit源码阅读之ASLayoutElementPrivate.h

仅列出一些比较关键的点
可以看到里面定义的变量类型十分严谨，清楚地指定了类型的大小

AS_EXTERN int32_t const ASLayoutElementContextInvalidTransitionID;
AS_EXTERN int32_t const ASLayoutElementContextDefaultTransitionID;

在处理数组时，可以看到定义是很清晰的，通过定义静态常量来定义数组的大小，更加直观。

static const int kMaxLayoutElementBoolExtensions = 1;
static const int kMaxLayoutElementStateIntegerExtensions = 4;
static const int kMaxLayoutElementStateEdgeInsetExtensions = 1;

typedef struct ASLayoutElementStyleExtensions {
  // Values to store extensions
  BOOL boolExtensions[kMaxLayoutElementBoolExtensions];
  NSInteger integerExtensions[kMaxLayoutElementStateIntegerExtensions];
  UIEdgeInsets edgeInsetsExtensions[kMaxLayoutElementStateEdgeInsetExtensions];
} ASLayoutElementStyleExtensions;

通过宏定义了一些函数的默认实现

#define ASLayoutElementLayoutCalculationDefaults \
- (ASLayout *)layoutThatFits:(ASSizeRange)constrainedSize\
{\
  return [self layoutThatFits:constrainedSize parentSize:constrainedSize.max];\
}\
\
- (ASLayout *)layoutThatFits:(ASSizeRange)constrainedSize parentSize:(CGSize)parentSize\
{\
  return [self calculateLayoutThatFits:constrainedSize restrictedToSize:self.style.size relativeToParentSize:parentSize];\
}\
\
- (ASLayout *)calculateLayoutThatFits:(ASSizeRange)constrainedSize\
                     restrictedToSize:(ASLayoutElementSize)size\
                 relativeToParentSize:(CGSize)parentSize\
{\
  const ASSizeRange resolvedRange = ASSizeRangeIntersect(constrainedSize, ASLayoutElementSizeResolve(self.style.size, parentSize));\
  return [self calculateLayoutThatFits:resolvedRange];\
}\

#define ASLayoutElementStyleExtensibilityForwarding \
- (void)setLayoutOptionExtensionBool:(BOOL)value atIndex:(int)idx\
{\
  [self.style setLayoutOptionExtensionBool:value atIndex:idx];\
}\
\
- (BOOL)layoutOptionExtensionBoolAtIndex:(int)idx\
{\
  return [self.style layoutOptionExtensionBoolAtIndex:idx];\
}\
\
- (void)setLayoutOptionExtensionInteger:(NSInteger)value atIndex:(int)idx\
{\
  [self.style setLayoutOptionExtensionInteger:value atIndex:idx];\
}\
\
- (NSInteger)layoutOptionExtensionIntegerAtIndex:(int)idx\
{\
  return [self.style layoutOptionExtensionIntegerAtIndex:idx];\
}\
\
- (void)setLayoutOptionExtensionEdgeInsets:(UIEdgeInsets)value atIndex:(int)idx\
{\
  [self.style setLayoutOptionExtensionEdgeInsets:value atIndex:idx];\
}\
\
- (UIEdgeInsets)layoutOptionExtensionEdgeInsetsAtIndex:(int)idx\
{\
  return [self.style layoutOptionExtensionEdgeInsetsAtIndex:idx];\
}\