前言:近期看了一下RAC中的宏命令,發(fā)現(xiàn)其中的宏命令一環(huán)扣一環(huán),環(huán)環(huán)相扣,把我都給整懵逼了...
通過深入學(xué)習(xí),終于能看懂了,寫個(gè)小demo秀一波操作.
源碼:
#define JK_Prepare_Subviews(supperView, ...)\
JK_metamacro_foreach(JK_Add_Subview, supperView, __VA_ARGS__)
#define JK_metamacro_foreach(Marco, supperView, ...)\
JK_metamacro_concat(JK_metamacro_foreach, JK_metamacro_argcount(__VA_ARGS__))(Marco, supperView, __VA_ARGS__)
#define JK_metamacro_foreach20(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18, _19)\
JK_metamacro_foreach19(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18)\
Marco(Parameter, _19, 19)
#define JK_metamacro_foreach19(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18)\
JK_metamacro_foreach18(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17)\
Marco(Parameter, _18, 18)
#define JK_metamacro_foreach18(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17)\
JK_metamacro_foreach17(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16)\
Marco(Parameter, _17, 17)
#define JK_metamacro_foreach17(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16)\
JK_metamacro_foreach16(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15)\
Marco(Parameter, _16, 16)
#define JK_metamacro_foreach16(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15)\
JK_metamacro_foreach15(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14)\
Marco(Parameter, _15, 15)
#define JK_metamacro_foreach15(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14)\
JK_metamacro_foreach14(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13)\
Marco(Parameter, _14, 14)
#define JK_metamacro_foreach14(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13)\
JK_metamacro_foreach13(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12)\
Marco(Parameter, _13, 13)
#define JK_metamacro_foreach13(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12)\
JK_metamacro_foreach12(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11)\
Marco(Parameter, _12, 12)
#define JK_metamacro_foreach12(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11)\
JK_metamacro_foreach11(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10)\
Marco(Parameter, _11, 11)
#define JK_metamacro_foreach11(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10)\
JK_metamacro_foreach10(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9)\
Marco(Parameter, _10, 10)
#define JK_metamacro_foreach10(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8, _9)\
JK_metamacro_foreach9(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8)\
Marco(Parameter, _9, 9)
#define JK_metamacro_foreach9(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7, _8)\
JK_metamacro_foreach8(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7)\
Marco(Parameter, _8, 8)
#define JK_metamacro_foreach8(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6, _7)\
JK_metamacro_foreach7(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6)\
Marco(Parameter, _7, 7)
#define JK_metamacro_foreach7(Marco, Parameter, _0, _1, _2, _3, _4, _5, _6)\
JK_metamacro_foreach6(Marco, Parameter, _0, _1, _2, _3, _4, _5)\
Marco(Parameter, _6, 6)
#define JK_metamacro_foreach6(Marco, Parameter, _0, _1, _2, _3, _4, _5)\
JK_metamacro_foreach5(Marco, Parameter, _0, _1, _2, _3, _4)\
Marco(Parameter, _5, 5)
#define JK_metamacro_foreach5(Marco, Parameter, _0, _1, _2, _3, _4)\
JK_metamacro_foreach4(Marco, Parameter, _0, _1, _2, _3)\
Marco(Parameter, _4, 4)
#define JK_metamacro_foreach4(Marco, Parameter, _0, _1, _2, _3)\
JK_metamacro_foreach3(Marco, Parameter, _0, _1, _2)\
Marco(Parameter, _3, 3)
#define JK_metamacro_foreach3(Marco, Parameter, _0, _1, _2)\
JK_metamacro_foreach2(Marco, Parameter, _0, _1)\
Marco(Parameter, _2, 2)
#define JK_metamacro_foreach2(Marco, Parameter, _0, _1)\
JK_metamacro_foreach1(Marco, Parameter, _0)\
Marco(Parameter, _1, 1)
#define JK_metamacro_foreach1(Marco, Parameter, _0)\
Marco(Parameter, _0, 0)
#define JK_Add_Subview(supperView, suberView, Index)\
[supperView addSubview:suberView];
#define JK_metamacro_concat(A, B) \
JK_metamacro_concat_(A, B)
#define JK_metamacro_concat_(A, B) A ## B
#define JK_metamacro_argcount(...) \
JK_metamacro_at(20, __VA_ARGS__, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)
#define JK_metamacro_at(N, ...) \
JK_metamacro_concat_(JK_metamacro_at, 20)(__VA_ARGS__, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)
#define JK_metamacro_at20(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18, _19, ...) JK_metamacro_head(__VA_ARGS__)
#define JK_metamacro_head(...) \
JK_metamacro_head_(__VA_ARGS__, 0)
//得到結(jié)果: 參數(shù)個(gè)數(shù)
#define JK_metamacro_head_(FIRST, ...) FIRST
試用一下:
- (void)viewDidLoad {
[super viewDidLoad];
NSMutableArray *marr = [NSMutableArray array];
CGFloat margin = 5;
CGFloat y;
CGFloat height = 20;
for (int i = 0; i < 21; i++) {
y = height * i + margin * (i + 1);
UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(0, y, 375, height)];
label.text = [NSString stringWithFormat:@"第%d行",i];
label.backgroundColor = [UIColor colorWithRed:arc4random_uniform(255)/255.0 green:arc4random_uniform(255)/255.0 blue:arc4random_uniform(255)/255.0 alpha:1];
[marr addObject:label];
}
JK_Prepare_Subviews(self.view, marr[0], marr[1], marr[2], marr[3], marr[4], marr[5] ,marr[6], marr[7], marr[8], marr[9], marr[10], marr[11], marr[12], marr[13], marr[14], marr[15], marr[16], marr[17], marr[18], marr[19]);
}
是不是看不懂?
實(shí)例解析:傳入三個(gè)參數(shù):a, b, c
JK_Prepare_Subviews(supperView, a, b, c)
#define JK_Prepare_Subviews(supperView, ...)\
JK_metamacro_foreach(JK_metamacro_foreach, supperView, __VA_ARGS__)
第一次展開
JK_metamacro_foreach(JK_metamacro_foreach, supperView, a, b, c)
#define JK_metamacro_foreach(Marco, supperView, ...)\
JK_metamacro_concat(JK_metamacro_foreach, JK_metamacro_argcount(__VA_ARGS__))(Marco, supperView, __VA_ARGS__)
第二次展開
JK_metamacro_concat(JK_metamacro_foreach, JK_metamacro_argcount(a, b, c))(JK_Add_Subview, supperView, a, b, c)
參數(shù)中的宏展開
#define JK_metamacro_argcount(...) \
JK_metamacro_at(20, a, b, c, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)
#define JK_metamacro_at(N, ...) \
JK_metamacro_concat_(JK_metamacro_at, 20)(a, b, c, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)
截取之后就剩下了3, 2, 1? {_0 ~ _19這20個(gè)參數(shù)(a, b, c, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4)在這邊沒有傳遞到下一個(gè)宏中}
#define JK_metamacro_at20(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18, _19, ...) JK_metamacro_head(3, 2, 1)
#define JK_metamacro_head(...) \
JK_metamacro_head_(3, 2, 1, 0)
得到結(jié)果: 參數(shù)個(gè)數(shù)
#define JK_metamacro_head_(FIRST, ...) 3
#define JK_metamacro_concat(A, B) \
JK_metamacro_concat_(A, B)
第三次展開
JK_metamacro_concat_(JK_metamacro_foreach, 3)(JK_Add_Subview, supperView, a, b, c)
#define JK_metamacro_concat_(A, B) A ## B? ? ? //拼接宏,結(jié)果為AB
第四次展開
JK_metamacro_foreach3(JK_Add_Subview, supperView, a, b, c)
#define JK_metamacro_foreach3(Marco, Parameter, _0, _1, _2)\
JK_metamacro_foreach2(Marco, Parameter, _0, _1)\
Marco(Parameter, _2, 2)
第五次展開
JK_metamacro_foreach2(JK_Add_Subview, supperView, a, b)
JK_Add_Subview(supperView, c)
#define JK_metamacro_foreach2(Marco, Parameter, _0, _1)\
JK_metamacro_foreach1(Marco, Parameter, _0)\
Marco(Parameter, _1, 1)
第六次展開
JK_metamacro_foreach1(JK_Add_Subview, supperView, a)
JK_Add_Subview(supperView, b)
JK_Add_Subview(supperView, c)
第七次展開
JK_Add_Subview(supperView, a)
JK_Add_Subview(supperView, b)
JK_Add_Subview(supperView, c)
結(jié)果:
宏定義其實(shí)就是是替換,
JK_Prepare_Subviews(supperView, a, b, c)
層層展開,最后替換之后就變成了
JK_Add_Subview(supperView, a)
JK_Add_Subview(supperView, b)
JK_Add_Subview(supperView, c)
