OC基础_分类:
分类的定义:分类是OC中的特有语法，它是表示一个指向分类结构体的指针，它是为了扩展系统类的方法而产生的一种方式。
分类的作用:
1.声明私有方法
2.分解体积庞大的类方法
3.把framework的私有方法公开
分类的特点:1.运行时决议(在iOS中，当原有类的方法不够用时，这时候分类就出现了。Category是在现有类的基础上添加新的方法，利用Objective-C 的动态运行时分配机制，可以为现有类添加新方法。可以在分类中添加方法和成员变量，但是添加的成员变量不会自动生成setter和getter方法，需要在实现部分给出实现。) 2.可以为系统类添加分类(不能给系统类添加扩展)
分类中可以添加哪些内容:1.实例方法 2.类方法 3.协议 4.属性(实际只做声明,未实现setter和getter方法.)
struct objc_category {
//分类名称
char * _Nonnull category_name OBJC2_UNAVAILABLE; //unavailable in objc 2.0, deprecated in Leopard
//宿主类
char * _Nonnull class_name OBJC2_UNAVAILABLE;
//实例方法列表
struct objc_method_list * _Nullable instance_methods OBJC2_UNAVAILABLE;
//类方法类表
struct objc_method_list * _Nullable class_methods OBJC2_UNAVAILABLE;
//协议列表
struct objc_protocol_list * _Nullable protocols OBJC2_UNAVAILABLE;
} OBJC2_UNAVAILABLE;
属性操作方式:例如我在分类.h文件中声明了一个可变数组
@property (nonatomic,strong)NSMutableArray *dataArray;
在.m文件中要实现
//getter方法
- (NSMutableArray *)dataArray{
return objc_getAssociatedObject(self, "dataArray");
}
//setter方法
- (void)setDataArray:(NSMutableArray *)dataArray{
objc_setAssociatedObject(self, "dataArray", dataArray,OBJC_ASSOCIATION_RETAIN);
}
分类的加载调用栈:
_objc_init->map_images->map_images_nolock->_read_images->methodizeClass
_objc_init 方法的实现源码:
void _objc_init(void)
{
static bool initialized = false;
if (initialized) return;
initialized = true;
// fixme defer initialization until an objc-using image is found?
environ_init();
tls_init();
static_init();
runtime_init();
exception_init();
cache_init();
_imp_implementationWithBlock_init();
//方法注册了对dyld中关于加载images的事件回调(下面是原始方法)
//void _dyld_objc_notify_register(_dyld_objc_notify_mapped mapped,_dyld_objc_notify_init init,_dyld_objc_notify_unmapped unmapped);
//分别注册了那些事件呢？根据注释，我们可以知道，共注册了三个事件的回调：
//_dyld_objc_notify_mapped ： OC image被加载映射到内存（+load()方法在此时被调用）
//_dyld_objc_notify_init ： OC image被init时
//_dyld_objc_notify_unmapped ： OC image被移除内存时
_dyld_objc_notify_register(&map_images, load_images, unmap_image);
#if __OBJC2__
didCallDyldNotifyRegister = true;
#endif
}
当image被dyld加载到内存后，会调用回调_dyld_objc_notify_mapped 。在runtime中，对应的函数是map_images下面是源码:
void map_images(unsigned count, const char * const paths[],
const struct mach_header * const mhdrs[])
{
mutex_locker_t lock(runtimeLock);
// map_images方法实质上会调用map_images_nolock方法。
// 而在map_images_nolock内部，又调用了_read_images方法，
// 其核心是用来读取Mach-O格式文件的runtime相关的section信息，
// 并转化为runtime内部的数据结构
return map_images_nolock(count, paths, mhdrs);
}
map_images_nolock方法下面是源码:
void
map_images_nolock(unsigned mhCount, const char * const mhPaths[],
const struct mach_header * const mhdrs[])
{
static bool firstTime = YES;
header_info *hList[mhCount];
uint32_t hCount;
size_t selrefCount = 0;
// Perform first-time initialization if necessary.
// This function is called before ordinary library initializers.
// fixme defer initialization until an objc-using image is found?
if (firstTime) {
preopt_init();
}
if (PrintImages) {
_objc_inform("IMAGES: processing %u newly-mapped images...\n", mhCount);
}
// Find all images with Objective-C metadata.
hCount = 0;
// Count classes. Size various table based on the total.
int totalClasses = 0;
int unoptimizedTotalClasses = 0;
{
uint32_t i = mhCount;
while (i--) {
const headerType *mhdr = (const headerType *)mhdrs[i];
auto hi = addHeader(mhdr, mhPaths[i], totalClasses, unoptimizedTotalClasses);
if (!hi) {
// no objc data in this entry
continue;
}
if (mhdr->filetype == MH_EXECUTE) {
// Size some data structures based on main executable's size
#if __OBJC2__
size_t count;
_getObjc2SelectorRefs(hi, &count);
selrefCount += count;
_getObjc2MessageRefs(hi, &count);
selrefCount += count;
#else
_getObjcSelectorRefs(hi, &selrefCount);
#endif
#if SUPPORT_GC_COMPAT
// Halt if this is a GC app.
if (shouldRejectGCApp(hi)) {
_objc_fatal_with_reason
(OBJC_EXIT_REASON_GC_NOT_SUPPORTED,
OS_REASON_FLAG_CONSISTENT_FAILURE,
"Objective-C garbage collection "
"is no longer supported.");
}
#endif
}
hList[hCount++] = hi;
if (PrintImages) {
_objc_inform("IMAGES: loading image for %s%s%s%s%s\n",
hi->fname(),
mhdr->filetype == MH_BUNDLE ? " (bundle)" : "",
hi->info()->isReplacement() ? " (replacement)" : "",
hi->info()->hasCategoryClassProperties() ? " (has class properties)" : "",
hi->info()->optimizedByDyld()?" (preoptimized)":"");
}
}
}
// Perform one-time runtime initialization that must be deferred until
// the executable itself is found. This needs to be done before
// further initialization.
// (The executable may not be present in this infoList if the
// executable does not contain Objective-C code but Objective-C
// is dynamically loaded later.
if (firstTime) {
sel_init(selrefCount);
arr_init();
#if SUPPORT_GC_COMPAT
// Reject any GC images linked to the main executable.
// We already rejected the app itself above.
// Images loaded after launch will be rejected by dyld.
for (uint32_t i = 0; i < hCount; i++) {
auto hi = hList[i];
auto mh = hi->mhdr();
if (mh->filetype != MH_EXECUTE && shouldRejectGCImage(mh)) {
_objc_fatal_with_reason
(OBJC_EXIT_REASON_GC_NOT_SUPPORTED,
OS_REASON_FLAG_CONSISTENT_FAILURE,
"%s requires Objective-C garbage collection "
"which is no longer supported.", hi->fname());
}
}
#endif
#if TARGET_OS_OSX
// Disable +initialize fork safety if the app is too old (< 10.13).
// Disable +initialize fork safety if the app has a
// __DATA,__objc_fork_ok section.
if (dyld_get_program_sdk_version() < DYLD_MACOSX_VERSION_10_13) {
DisableInitializeForkSafety = true;
if (PrintInitializing) {
_objc_inform("INITIALIZE: disabling +initialize fork "
"safety enforcement because the app is "
"too old (SDK version " SDK_FORMAT ")",
FORMAT_SDK(dyld_get_program_sdk_version()));
}
}
for (uint32_t i = 0; i < hCount; i++) {
auto hi = hList[i];
auto mh = hi->mhdr();
if (mh->filetype != MH_EXECUTE) continue;
unsigned long size;
if (getsectiondata(hi->mhdr(), "__DATA", "__objc_fork_ok", &size)) {
DisableInitializeForkSafety = true;
if (PrintInitializing) {
_objc_inform("INITIALIZE: disabling +initialize fork "
"safety enforcement because the app has "
"a __DATA,__objc_fork_ok section");
}
}
break; // assume only one MH_EXECUTE image
}
#endif
}
//这里是核心代码区
if (hCount > 0) {
_read_images(hList, hCount, totalClasses, unoptimizedTotalClasses);
}
firstTime = NO;
// Call image load funcs after everything is set up.
for (auto func : loadImageFuncs) {
for (uint32_t i = 0; i < mhCount; i++) {
func(mhdrs[i]);
}
}
}
methodizeClass的方法实现源码:
static void methodizeClass(Class cls, Class previously)
{
runtimeLock.assertLocked();
bool isMeta = cls->isMetaClass();
auto rw = cls->data();
auto ro = rw->ro();
auto rwe = rw->ext();
// Methodizing for the first time
if (PrintConnecting) {
_objc_inform("CLASS: methodizing class '%s' %s",
cls->nameForLogging(), isMeta ? "(meta)" : "");
}
// Install methods and properties that the class implements itself.
method_list_t *list = ro->baseMethods();
if (list) {
prepareMethodLists(cls, &list, 1, YES, isBundleClass(cls));
if (rwe) rwe->methods.attachLists(&list, 1);
}
property_list_t *proplist = ro->baseProperties;
if (rwe && proplist) {
rwe->properties.attachLists(&proplist, 1);
}
protocol_list_t *protolist = ro->baseProtocols;
if (rwe && protolist) {
rwe->protocols.attachLists(&protolist, 1);
}
// Root classes get bonus method implementations if they don't have
// them already. These apply before category replacements.
if (cls->isRootMetaclass()) {
// root metaclass
addMethod(cls, @selector(initialize), (IMP)&objc_noop_imp, "", NO);
}
// Attach categories.
if (previously) {
if (isMeta) {
objc::unattachedCategories.attachToClass(cls, previously,
ATTACH_METACLASS);
} else {
// When a class relocates, categories with class methods
// may be registered on the class itself rather than on
// the metaclass. Tell attachToClass to look for those.
objc::unattachedCategories.attachToClass(cls, previously,
ATTACH_CLASS_AND_METACLASS);
}
}
objc::unattachedCategories.attachToClass(cls, cls,
isMeta ? ATTACH_METACLASS : ATTACH_CLASS);
#if DEBUG
// Debug: sanity-check all SELs; log method list contents
for (const auto& meth : rw->methods()) {
if (PrintConnecting) {
_objc_inform("METHOD %c[%s %s]", isMeta ? '+' : '-',
cls->nameForLogging(), sel_getName(meth.name));
}
ASSERT(sel_registerName(sel_getName(meth.name)) == meth.name);
}
#endif
}
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