How does iOS compare the equality of two objects?

Source: Internet
Author: User

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?

Related Article

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.