New features for iOS

1, the declaration attribute can be empty three kinds of wording:

1, @property (nonatomic, copy, nullable) NSString *name; 2, @property (nonatomic, copy) NSString *_nullable name1; 3, @property (nonatomic, copy) NSString *__nullable name2;

2, the declaration attribute can be empty three kinds of wording:

1, @property (nonatomic, copy, nonnull) NSString *name4; 2, @property (nonatomic, copy) NSString *_nonnull name5; 3, @property (nonatomic, copy) NSString *__nonnull name6;

Note: The above three kinds of writing the first one to use the most, the latter two basic not how to use

3. Between Ns_assume_nonnull_begin and Ns_assume_nonnull_end, all object properties and methods defined by default are nonnull

* * * * __nullablename2; Ns_assume_nonnull_end

///4, the usage in the method is as follows:

-(nonnull NSString *) Test: (Nullable NSString *) str; -(NSString * _nonnull) Test1: (NSString * _nonnull) str;

5, the use of null_resettable:

If you use Null_resettable, you must override the Get method or the Set method, and the process of passing the value to null is as follows (a setter or getter implements one)

@property (nonatomic, copy, null_resettable) NSString *name;//Implementing Setter Methods- (void) SetName: (NSString *) name{if(Name = =Nil) {Name=@"123"; } _name=name;}//Implement Getter-(NSString *) name{if(_name = =Nil) {_name=@"123"; }    return_name;}

6. Declare the type of object in the array: Add < data type *> after type, and then warn, crash if insert non-string type in data

@property (nonatomic, strong) nsmutablearray<nsstring *> *dataarray;

7, __kindof use: __kindof: Represents the current class or its subclasses,
__KINDOF writing format: Put in front of the type, indicating the type of decoration (__kindof person *),
__kindof: When called, it is clear that the return type is known.
Note: Of course, you can also write + (instancetype) person; The return value is instancetype.
Example: Create a new Person class

//. h in@interfacePerson:nsobject+ (__kindof person *) person;+ (Person *) Person1;@end//. M Medium@implementation Person//indicates that the return data type is person or its child class object+ (__kindof person *) person{return[[Self alloc] init];}+ (Person *) person1{return[[Self alloc] init];}@end//Create person Subclass Sonperson@interfaceSonperson:person@end//at this point Sonperson calls the parent class method + (__kindof person *) The person returns the Sonperson object//Normal returnSonperson *son =[Sonperson person];//The object returned is the person objectSonperson *son1 = [Sonperson Person1];

8, __covariant (covariant), __contravariant (contravariant) __covariant (covariant): For the generic data strong-turn type, can be strong, the subclass can be turned to the parent class __contravariant (contravariant): For the generic data strong-to type, can go down strongly, the parent class can be turned into a subclass instance: Create the language class, while creating iOS, Java Two classes inherit from language, in the Create Person class, where the person class code:

#import<Foundation/Foundation.h>#import "Language.h"#import "IOS.h"//declaring generics@interfacePerson<__contravariant objecttype>: NSObject//language@property (nonatomic) ObjectType language;//ID: Any object can be passed in//language: When called outside, there is no hint//ios*You can only pass objects later .-(ObjectType) language;- (void) SetLanguage: (ObjectType) language; @end //Controller inPerson<language *> *p =[[Person alloc] init]; person<ios *> *iosp =[[Person alloc] init];//if the subclass wants to assign a value to the parent class, the covariantIOSP =p;//generics are not deterministic, that is, ID typeIosp.language = [[IOS alloc] init];

PS: Temporary is some simple application

New features for iOS