上篇分析類結(jié)構(gòu)蜡感，獲取到了屬性列表 property_array_t 和方法列表 method_array_t呻待。
實(shí)踐代碼：
@interface GLPerson : NSObject
@property (nonatomic, strong) NSString *name; /**< 8個(gè)字節(jié) */
@property (nonatomic, strong) NSString *nickName; /**< 8個(gè)字節(jié) */
- (void)sayHello;
+ (void)goSchool;
@end
@interface GLStudent : GLPerson
@end
一、類的類方法存儲(chǔ)
通過源碼查看趁怔，沒有看到底層把 method 區(qū)分類方法還是實(shí)例方法湿硝。既然實(shí)例方法存在類對(duì)象中薪前，類方法是不是可能存在元類中。試著通過 lldb 打印一下关斜。
(lldb) x/4gx GLPerson.class
0x1000022b8: 0x0000000100002290 0x0000000100333140
0x1000022c8: 0x000000010113f640 0x0001802400000003
(lldb) p 0x0000000100002290 & 0x00007ffffffffff8ULL // 通過isa找到元類
(unsigned long long) $1 = 4294976144
(lldb) x/4gx $1 // 讀取元類的內(nèi)存
0x100002290: 0x00000001003330f0 0x00000001003330f0
0x1000022a0: 0x0000000100643250 0x0001e03500000007
(lldb) p (class_data_bits_t *)0x1000022b0 // 通過偏移32字節(jié)獲取class_data_bits_t指針
(class_data_bits_t *) $2 = 0x00000001000022b0
(lldb) p *$2->data() // 調(diào)用class_data_bits_t 的data方法獲取class_rw_t
(class_rw_t) $3 = {
flags = 2684878849
witness = 1
ro_or_rw_ext = {
std::__1::atomic<unsigned long> = 4294975528
}
firstSubclass = 0x00000001000022e0
nextSiblingClass = 0x00007fff88bf1948
}
(lldb) p $3.methods() // 打印元類的方法列表
(const method_array_t) $4 = {
list_array_tt<method_t, method_list_t> = {
= {
list = 0x0000000100002070
arrayAndFlag = 4294975600
}
}
}
(lldb) p $4.list
(method_list_t *const) $5 = 0x0000000100002070
(lldb) p *$5
(method_list_t) $6 = {
entsize_list_tt<method_t, method_list_t, 3> = {
entsizeAndFlags = 26
count = 1
first = {
name = "goSchool"
types = 0x0000000100000f7c "v16@0:8"
imp = 0x0000000100000d70 (`+[GLPerson goSchool])
}
}
}
(lldb) p $6.get(0) // 第一個(gè)就是聲明的類方法
(method_t) $7 = {
name = "goSchool"
types = 0x0000000100000f7c "v16@0:8"
imp = 0x0000000100000d70 (`+[GLPerson goSchool])
}
(lldb) p $6.get(1) // 只有一個(gè)類方法示括，下一個(gè)越界了
Assertion failed: (i < count), function get, file /Users/xulong/Desktop/學(xué)習(xí)/alloc流程分析/runtime/objc-runtime-new.h, line 438.
error: Execution was interrupted, reason: signal SIGABRT.
The process has been returned to the state before expression evaluation.
通過上面代碼發(fā)現(xiàn)：
- 方法存儲(chǔ)的時(shí)候是沒有明確的區(qū)分是類方法還是實(shí)例方法的；
- 實(shí)例方法存儲(chǔ)在類的數(shù)據(jù)中痢畜；
- 類方法存儲(chǔ)在元類的數(shù)據(jù)中例诀；
1.1 通過runtime源碼分析
runtime 里面有方法:
-
class_getInstanceMethod: 返回一個(gè)類的指定實(shí)例方法； -
class_getClassMethod：返回一個(gè)類的指定類方法裁着；
const char *className = class_getName([GLPerson class]);
Class metaClass = objc_getMetaClass(className);
Method instanceM1 = class_getInstanceMethod([GLPerson class], @selector(sayHello));
Method instanceM2 = class_getInstanceMethod([GLPerson class], @selector(goSchool));
Method classM1 = class_getClassMethod([GLPerson class], @selector(sayHello));
Method classM2 = class_getClassMethod([GLPerson class], @selector(goSchool));
Method metaInstanceM1 = class_getInstanceMethod(metaClass, @selector(sayHello));
Method metaInstanceM2 = class_getInstanceMethod(metaClass, @selector(goSchool));
Method metaClassM1 = class_getClassMethod(metaClass, @selector(sayHello));
Method metaClassM2 = class_getClassMethod(metaClass, @selector(goSchool));
NSLog(@"instanceM1:%p; instanceM2:%p; classM1:%p; classM2:%p;", instanceM1, instanceM2, classM1, classM2);
NSLog(@"metaInstanceM1:%p; metaInstanceM2:%p; metaClassM1:%p; metaClassM2:%p;", metaInstanceM1, metaInstanceM2, metaClassM1, metaClassM2);
console: instanceM1:0x1000020f8; instanceM2:0x0; classM1:0x0; classM2:0x100002090;
console: metaInstanceM1:0x0; metaInstanceM2:0x1000020a0; metaClassM1:0x0; metaClassM2:0x1000020a0;
分析一下
第一行類輸出：代表類有無
-
instanceM1有值： 有sayHello實(shí)例方法繁涂，instanceM2沒值： 沒有goSchool實(shí)例方法； -
classM1沒值：沒有sayHello類方法二驰，classM2有值：有goSchool類方法扔罪；
第二行元類輸出：代表元類有無
-
metaInstanceM1沒值： 沒有sayHello實(shí)例方法，metaInstanceM2有值： 有goSchool實(shí)例方法桶雀； -
metaClassM1沒值：沒有sayHello類方法矿酵，metaClassM2有值：有goSchool類方法；
這里先看下 class_getClassMethod 的源碼：
Method class_getClassMethod(Class cls, SEL sel)
{
if (!cls || !sel) return nil;
return class_getInstanceMethod(cls->getMeta(), sel);
}
---
// NOT identical to this->ISA when this is a metaclass
Class getMeta() {
if (isMetaClass()) return (Class)this;
else return this->ISA();
}
class_getClassMethod 的流程：
-
class_getClassMethod里面調(diào)用的也是class_getInstanceMethod; - 只不過傳的類是
cls->getMeta()這個(gè)方法返回的; -
getMeta如果是元類矗积，返回的就是自己全肮； -
getMeta如果不是元類，返回的是ISA(); - 類的
ISA()返回的是 該類的元類;
class_getClassMethod總結(jié)：
- 如果傳的類棘捣，里面是獲取的元類的
class_getInstanceMethod方法辜腺。也既類方法是從元類里面去找的。 - 如果傳的是元類乍恐，直接用元類調(diào)用
class_getInstanceMethod方法评疗。
二、是不是這個(gè)類 isKindOfClass & isMemberOfClass
首先有這樣一段代碼：
BOOL obClass_k = [(id)[NSObject class] isKindOfClass:[NSObject class]]; //
BOOL obClass_m = [(id)[NSObject class] isMemberOfClass:[NSObject class]]; //
BOOL peClass_k = [(id)[GLPerson class] isKindOfClass:[GLPerson class]]; //
BOOL peClass_m = [(id)[GLPerson class] isMemberOfClass:[GLPerson class]]; //
NSLog(@"\n obClass_k :%hhd\n obClass_m :%hhd\n peClass_k :%hhd\n peClass_m :%hhd\n",obClass_k, obClass_m, peClass_k, peClass_m);
BOOL obInstance_k = [(id)[NSObject alloc] isKindOfClass:[NSObject class]]; //
BOOL obInstance_m = [(id)[NSObject alloc] isMemberOfClass:[NSObject class]]; //
BOOL peInstance_k = [(id)[GLPerson alloc] isKindOfClass:[GLPerson class]]; //
BOOL peInstance_m = [(id)[GLPerson alloc] isMemberOfClass:[GLPerson class]]; //
NSLog(@"\n obInstance_k :%hhd\n obInstance_m :%hhd\n peInstance_k :%hhd\n peInstance_m :%hhd\n",obInstance_k, obInstance_m, peInstance_k, peInstance_m);
console:
obClass_k :1
obClass_m :0
peClass_k :0
peClass_m :0
---
obInstance_k :1
obInstance_m :1
peInstance_k :1
peInstance_m :1
可找到上面調(diào)用的具體源碼如下：
// 類方法調(diào)用
+ (BOOL)isKindOfClass:(Class)cls {
for (Class tcls = self->ISA(); tcls; tcls = tcls->superclass) {
if (tcls == cls) return YES;
}
return NO;
}
+ (BOOL)isMemberOfClass:(Class)cls {
return self->ISA() == cls;
}
// 實(shí)例方法調(diào)用
- (BOOL)isKindOfClass:(Class)cls {
for (Class tcls = [self class]; tcls; tcls = tcls->superclass) {
if (tcls == cls) return YES;
}
return NO;
}
- (BOOL)isMemberOfClass:(Class)cls {
return [self class] == cls;
}
但是在實(shí)際調(diào)用的時(shí)候茵烈，斷點(diǎn)發(fā)現(xiàn) isKindOfClass 沒有走到 上面的源碼中百匆，通過匯編查看下具體走的什么方法
isKindOfClass匯編查看.png
發(fā)現(xiàn)調(diào)用的是objc_opt_isKindOfClass，what !!!呜投，猜測應(yīng)該是蘋果再 llvm 編譯時(shí)期做了操作加匈。
// Calls [obj isKindOfClass]
BOOL
objc_opt_isKindOfClass(id obj, Class otherClass)
{
#if __OBJC2__
if (slowpath(!obj)) return NO;
Class cls = obj->getIsa();
if (fastpath(!cls->hasCustomCore())) {
for (Class tcls = cls; tcls; tcls = tcls->superclass) {
if (tcls == otherClass) return YES;
}
return NO;
}
#endif
return ((BOOL(*)(id, SEL, Class))objc_msgSend)(obj, @selector(isKindOfClass:), otherClass);
}
-
分析1
[(id)[NSObject class] isKindOfClass:[NSObject class]];：-
[NSObject class]返回類自己; -
objc_opt_isKindOfClass中，obj為NSObject類仑荐，otherClass為NSObject類雕拼； -
Class cls首先賦值為NSObject的元類; -
Class tcls = cls，tcls賦值元類释漆，判斷tcls是否等于otherClass悲没，類不等于元類； - 把
tcls = tcls->superclass，NSObject元類的superclass為根類示姿，也就是[NSObject class]甜橱； -
tcls現(xiàn)在為NSObject類，所以和otherClass相等栈戳； - 返回
YES岂傲；
-
-
分析2
[(id)[NSObject class] isMemberOfClass:[NSObject class]]:-
[NSObject class]返回類自己，所以會(huì)調(diào)用類方法; -
self和cls都為NSObject類子檀； -
self->ISA()返回NSObject的元類镊掖； -
NSObject的元類和類不相等； - 返回
NO褂痰；
-
-
分析3
[(id)[GLPerson class] isKindOfClass:[GLPerson class]]:-
[GLPerson class]返回類自己亩进，所以會(huì)調(diào)用類方法; -
objc_opt_isKindOfClass中，obj為GLPerson類缩歪，otherClass為GLPerson類归薛； -
Class cls和Class tcls首先賦值為GLPerson的元類; -
tcls存在，判斷tcls是否等于otherClass匪蝙，類不等于元類主籍； - 把
tcls = tcls->superclass，GLPerson元類的superclass為根元類逛球，也就是[NSObject class]的元類千元； -
tcls現(xiàn)在為NSObject元類，不等于otherClass的GLPerson類颤绕； - 再次把
tcls = tcls->superclass幸海，NSObject元類的superclass為[NSObject class]類； -
tcls為NSObject類 不等于otherClass的GLPerson類屋厘； - 再再次
tcls = tcls->superclass涕烧，NSObject類的superclass為nil； -
tcls為nil; - 返回
NO汗洒；
-
-
分析4
[(id)[GLPerson class] isMemberOfClass:[GLPerson class]]:-
[GLPerson class]返回類自己，所以會(huì)調(diào)用類方法; -
self和cls都為GLPerson類父款； -
self->ISA()返回GLPerson的元類溢谤； -
GLPerson的元類和類不相等； - 返回
NO憨攒；
-
-
分析5
[(id)[NSObject alloc] isKindOfClass:[NSObject class]]:-
[NSObject alloc]是實(shí)例世杀； -
Class cls = obj->getIsa()，cls賦值為NSObject類肝集； -
Class cls和tcls賦值為NSObject類瞻坝，otherClass賦值為NSObject類；cls為[NSObject class]杏瞻； - 所以
tcls等于otherClass所刀，都是NSObject類衙荐； - 返回
YES;
-
-
分析6
[(id)[NSObject alloc] isMemberOfClass:[NSObject class]]:-
[NSObject alloc]是實(shí)例，所以會(huì)調(diào)用實(shí)例方法浮创； -
[self class]為 NSObject 類忧吟，cls為[NSObject class]； - 都是
NSObject類斩披； - 返回
YES;
-
-
分析7
[(id)[GLPerson alloc] isKindOfClass:[GLPerson class]]:-
[GLPerson alloc]是實(shí)例溜族； -
Class cls = obj->getIsa()，cls賦值為GLPerson類垦沉； -
Class cls和tcls賦值為GLPerson類煌抒，otherClass為GLPerson類； - 所以
tcls等于otherClass厕倍，都是GLPerson類摧玫； - 返回
YES;
-
-
分析8
[(id)[GLPerson alloc] isMemberOfClass:[GLPerson class]]:-
[GLPerson alloc]是實(shí)例，所以會(huì)調(diào)用實(shí)例方法绑青； -
[self class]為 GLPerson 類诬像，cls為[GLPerson class]； - 都是
GLPerson類闸婴； - 返回
YES;
-
