How does iOS compare the equality of two objects?

In iOS, if you use = = to compare two objects, the memory address of the object is compared, which is generally not enough to meet our needs.

For example, there is a person class, and when all properties of the person object are consistent, it is assumed that the two objects are equal and can be implemented in the following way.

@interface Person:nsobject

@property (nonatomic, copy) NSString *name;

@property (nonatomic, copy) NSString *country;

@property (nonatomic, copy) NSString *pid;

@end

@implementation person

-(BOOL) IsEqual: (ID) Object {

if (self = = object) {

return YES;

}

　　

if ([self class]! = [object class]) {

return NO;

}

Person *anotherperson = (person *) object;

if (![ _name IsEqualToString:anotherPerson.name]) {

return NO;

}

if (![ _country IsEqualToString:anotherPerson.country]) {

return NO;

}

if (![ _pid IsEqualToString:anotherPerson.pId]) {

return NO;

}

return YES;

}

-(Nsuinteger) hash {

Nsuinteger Namehash = [_name hash];

Nsuinteger Countryhash = [_country hash];

Nsuinteger Pidhash = [_pid hash];

return Namehash ^ Countryhash ^ pidhash;

}

@end

This basically satisfies the demand.

Similarly, we can implement a specific method of equality judgment, similar to the Isequaltostring method of the NSString class, which can be implemented in the following way.

@implementation person

-(BOOL) Isequaltoperson: (person *) Anotherperson {

if (self = = Anotherperson) {

return YES;

}

if (![ _name IsEqualToString:anotherPerson.name]) {

return NO;

}

if (![ _country IsEqualToString:anotherPerson.country]) {

return NO;

}

if (![ _pid IsEqualToString:anotherPerson.pId]) {

return NO;

}

return YES;

}

-(BOOL) IsEqual: (ID) Object {

if ([self class] = = [Object class]) {

return [self Isequaltoperson: (person *) object];

}else{

return [Super Isequal:object];

}

}

-(Nsuinteger) hash {

Nsuinteger Namehash = [_name hash];

Nsuinteger Countryhash = [_country hash];

Nsuinteger Pidhash = [_pid hash];

return Namehash ^ Countryhash ^ pidhash;

}

@end

Note: The same object must have the same hash code, but the two hashes of the same object are not necessarily the same.

In addition, when you use a container, you should not change its hash code if you put a mutable object into the container.

For example:

Nsmutableset *set = [[Nsmutableset alloc] init];

Nsmutablearray *arraya = [@[@1, @2] mutablecopy];

[Set Addobject:arraya];

NSLog (@ "%@", set); {()}

Nsmutablearray *arrayb = [@[@1] mutablecopy];

[Set Addobject:arrayb];

NSLog (@ "%@", set); {((1), ())}

[Arrayb addobject:@2];

NSLog (@ "%@", set); {((), ())}

Magically put two equal arrays in set. Sometimes there are some unexpected problems that need special attention.

How does iOS compare the equality of two objects?