在NSObject.mm文件中可以找到alloc方法和new方法的实现
***如果使用new的话,初始化方法就被固定调用init***
+ (id)new {
return [callAlloc(self, false/*checkNil*/) init];
}
+ (id)alloc {
return _objc_rootAlloc(self);
}
// Replaced by ObjectAlloc
+ (id)allocWithZone:(struct _NSZone *)zone {
return _objc_rootAllocWithZone(self, (malloc_zone_t *)zone);
}
// Base class implementation of +alloc. cls is not nil.
// Calls [cls allocWithZone:nil].
id
_objc_rootAlloc(Class cls)
{
return callAlloc(cls, false/*checkNil*/, true/*allocWithZone*/);
}
alloc参数allocWithZone 为 true
1.alloc---->allocWithZone--->true
2.初始化的方式,不但可以通过init还可以通过initXXX
new参数allocWithZone 为 false
- new---->allocWithZone--->false
- 初始化的方式,固定调用init
// Call [cls alloc] or [cls allocWithZone:nil], with appropriate
// shortcutting optimizations.
static ALWAYS_INLINE id
callAlloc(Class cls, bool checkNil, bool allocWithZone=false)
{
if (slowpath(checkNil && !cls)) return nil;
#if __OBJC2__
if (fastpath(!cls->ISA()->hasCustomAWZ())) {
// No alloc/allocWithZone implementation. Go straight to the allocator.
// fixme store hasCustomAWZ in the non-meta class and
// add it to canAllocFast's summary
if (fastpath(cls->canAllocFast())) {
// No ctors, raw isa, etc. Go straight to the metal.
bool dtor = cls->hasCxxDtor();
id obj = (id)calloc(1, cls->bits.fastInstanceSize());
if (slowpath(!obj)) return callBadAllocHandler(cls);
obj->initInstanceIsa(cls, dtor);
return obj;
}
else {
// Has ctor or raw isa or something. Use the slower path.
id obj = class_createInstance(cls, 0);
if (slowpath(!obj)) return callBadAllocHandler(cls);
return obj;
}
}
#endif
// No shortcuts available.
if (allocWithZone) return [cls allocWithZone:nil];
return [cls alloc];
}
是否重写allocWithZone:方法
- 没有重写allocWithZone:方法
[cls new]分配内存的方式和[cls alloc]分配方式是一样的, 都是通过id obj = class_createInstance(cls, 0);来分配 - 重写了allocWithZone:方法
[cls new]创建对象的方式[cls alloc]方法,
[cls alloc]创建对象的方式[cls allocWithZone:nil]方法
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