create
+ (instancetype)alloc OBJC_SWIFT_UNAVAILABLE("use object initializers instead");
+ (instancetype)allocWithZone:(struct _NSZone *)zone OBJC_SWIFT_UNAVAILABLE("use object initializers instead");
+ (instancetype)new OBJC_SWIFT_UNAVAILABLE("use object initializers instead");
- (instancetype)init
#if NS_ENFORCE_NSOBJECT_DESIGNATED_INITIALIZER
NS_DESIGNATED_INITIALIZER
#endif
;
注意:
- alloc和allocWithZone等价,历史原因,alloc调用allocWithZone,zone参数ignored,alloc简洁,习惯使用alloc
- alloc和allocWithZone初始化instance object的isa指向class object,其余数据成员初始化为0
- new是alloc+init,new符合c++的对象生成写法,但在oc中习惯使用alloc+init
- alloc和init的返回对象可能不同
- NSObject的init怎么也没做,只是返回self
copy
- (id)copy;
- (id)mutableCopy;
+ (id)copyWithZone:(struct _NSZone *)zone OBJC_ARC_UNAVAILABLE;
+ (id)mutableCopyWithZone:(struct _NSZone *)zone OBJC_ARC_UNAVAILABLE;
注意:
- copy调用-copyWithZone,mutableCopy调用-mutableCopyWithZone
- NSObject没有实现-copyWithZone和-mutableCopyWithZone,zone参数ignored
- -copyWithZone是NSCopying协议的Method
- -mutableCopyWithZone是NSMutableCopying协议的Method
- NSObject没有实现NSCopying协议和NSMutableCopying协议
- +copyWithZone返回class object,表示class object遵守NSCopying协议
- +mutableCopyWithZone返回class object,表示class object遵守NSMutableCopying协议
dealloc
- (void)dealloc OBJC_SWIFT_UNAVAILABLE("use 'deinit' to define a de-initializer");
注意:
- dealloc不要显式调用,runtime在RC = 0时自动调用
- NSObject的dealloc释放数据成员占据的内存空间,如果要释放除数据成员之外的资源,需override dealloc,释放这些资源
- ARC下override dealloc时无需显示调用 [super dealloc],编译器会在方法末插入 [super dealloc],MRC下override dealloc时需显式在方法末调用[super dealloc],否则子类可能访问父类已free的内存)