NSSet 不包含对象，即使它们是相等的

Question

Person class:

@interface Person : NSObject

@property (nonatomic, copy) NSString *name;

@end

我重写了它的 isEqual: 方法：

- (BOOL)isEqual:(id)object {
    Person *person = (Person *)object;
    return [self.name isEqualToString:person.name];
}

然后我做了一个测试：

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.

    Person *p1 = [[Person alloc] init];
    p1.name = @"Jack";

    Person *p2 = [[Person alloc] init];
    p2.name = @"Jack";

    if ([p1 isEqual:p2]) {
        NSLog(@"p1 isEqual p2");
    } else {
        NSLog(@"p1 not Equal p2");
    }

    NSMutableSet *set = [NSMutableSet set];
    [set addObject:p1];

    if ([set containsObject:p2]) {
        NSLog(@"contain p2");
    } else {
        NSLog(@"not contain p2");
    }
}

控制台打印：

p1 isEqual p2
not contain p2

关于方法containsObject::

Each element of the set is checked for equality with anObject until a match is found or the end of the set is reached. Objects are considered equal if isEqual: returns YES.

所以我现在有点困惑：

既然p1等于p2，为什么集合中不包含p2？

Answer 1

来自documentation for the NSObject protocol：

If two objects are equal, they must have the same hash value. This last point is particularly important if you define isEqual: in a subclass and intend to put instances of that subclass into a collection. Make sure you also define hash in your subclass.

NSSet 不包含对象，即使它们是相等的

NSSet didn't contain the object even though they are equal

objective-c

nsset