IOS development-Stage 4-memory management, ios Stage 4

IOS development-Stage 4-memory management, ios Stage 4

Deep copy and light copy

 

Only objects that implement the NSCoping protocol can be copied. The NSCopy Protocol is required for copying custom objects. Whether it is a deep copy or a shallow copy depends on how the protocol is implemented.

 

The Type obtained by copy must be unchangeable; The type obtained by mutableCopy must be variable.

Shallow copy: After the copy, the memory address (pointer) remains unchanged;

Deep copy: the memory address (pointer) changes after the copy;

For an immutable copy of an immutable type, it is a shortest copy, and for others, it is a deep copy (whether it is a copy type or a copy method );

 

1) NSString: copy a shortest copy. After the copy, NSString is immutable;

MutableCopy: Deep copy. After the copy, the NSMutableString variable;

2) NSMutableString: copy deep copy. After the copy, NSString is immutable;

MutableCopy: Deep copy. After the copy, the NSMutableString variable;

(NSArray, NAMutableArray) (NSDictionary, NSMutableDictionary) NSSet (SET) is similar

3) A Strong is attached to copy.

4) @ autoreleasepool {} Automatically releases the pool. An object is released when an object is created in the for loop.

(5) NSAID utoreleasepool * pool = [NSAID utoreleasepool alloc] init];

 

Note:

Error code: @ property (nonatomic, copy) NSMutableArray * mutableArray;

When using this method, you must rewrite its set placement method;

Correct syntax: @ property (nonatomic, retain) NSMutableArray * mutableArray;

 

ARC

The [super delloc] Method in ARC cannot be called, but the delloc method is still valid. Therefore, you can still [[nsicationicationcenter defacenter center] removeObser: self];

 

Strong, Weak

1) if Strong is a Strong reference, the object pointed by strong pointer will never be released. If no Strong pointer points to it, it will be released immediately;

2) weak is a weak application. It is automatically set to null when its objects are released. objects without Strong or weak pointers are _ strong by default;

3) in ARC, the @ property retain object will be automatically compiled into Strong during compilation.

4) strong and weak do not modify simple types. assgin or unsafe_unretained is used for simple types.

5) in the ARC block, we used _ block to prevent circular references. Now we use weak;

 

Add a non-ARC file in the ARC environment:-fno-objc-arc

Add the ARC file-fobjc-ARC in a non-arc environment

 

Expansion:

Conversion, bridging

1). m OC and C can be directly mixed;

2). m --->. mm OC and C, C ++ mixing;

3). cpp C and C ++ are not mixed with OC;

4) _ bridge_retained OC ---> C is retaken once during conversion. (This is a global method and the method must be a method declared in. h );

5) _ bridge_transfer C ---> the OC will be release once during conversion;

6) _ bridge C <---> no changes are made to the reference count when OC is converted to each other. (The method must be a method declared in. h );