OC中自定义类的NSCopying实现的注意事项(isEqual & hash实现)

在OC中，如果自定义类，则要考虑赋值、持久化保存、保存到其它容器中等各种情况的对象复制和比较，下面是一个比较全面的自定义例子，在此仅作记录：

自定义类：

KeyValuePairs.h：

#import <Foundation/Foundation.h>

@interface KeyValuePairs: NSObject <NSCopying>
@property (nonatomic,strong)NSString *identifier;
@property (nonatomic,strong)NSString *name;

@end

KeyValuePairs.m：

#import "KeyValuePairs.h"

@implementation KeyValuePairs

- (id)copyWithZone:(NSZone *)zone
{
KeyValuePairs *kvp = [[[self class] allocWithZone:zone] init];
kvp.identifier = self.identifier;
kvp.name = self.name;
return kvp;
}

- (BOOL)isEqualToKeyValuePairs:(KeyValuePairs *)kvp{
if (!kvp) {
return NO;
}
BOOL haveEqualName = (!self.name && !kvp.name) || [self.name isEqualToString:kvp.name];
BOOL haveEqualIdentifier = (!self.identifier && !kvp.identifier) || [self.identifier isEqualToString:kvp.identifier];

return haveEqualName && haveEqualIdentifier;
}

#pragma mark -NSObject
-(BOOL)isEqual:(id)object{
if (self == object) {
return YES;
}
if (![object isKindOfClass:[KeyValuePairs class]]) {
return NO;
}
return [self isEqualToKeyValuePairs:(KeyValuePairs *)object];
}

- (NSUInteger)hash {
return [self.name hash] ^ [self.identifier hash];
}

@end

测试：

NSMutableDictionary *namesWillUpdateDic = [[NSMutableDictionary alloc] init];
NSMutableArray *names = [[NSMutableArray alloc] init];
for (int i = 0; i<1000; i++) {
NSString *name = [NSString stringWithFormat:@"%d_zhangsan",i];
NSString *identifier = [NSString stringWithFormat:@"%d_identifier",i];
NSString *strObj = [NSString stringWithFormat:@"%d_strObj",i];
KeyValuePairs *kvp = [[KeyValuePairs alloc] init];
kvp.identifier = identifier;
kvp.name = name;
[namesWillUpdateDic setObject:strObj forKey:kvp];
[names addObject:kvp];
}

for (int j = 0; j<1000; j++) {
int index = arc4random()%1000;
KeyValuePairs *kvp = [names objectAtIndex:index];
NSString *strObj = [namesWillUpdateDic objectForKey:kvp];
NSString *msg = [NSString stringWithFormat:@"index:%d,identifier:%@,email:%@,strObj:%@",index,kvp.identifier,kvp.name,strObj];
NSLog(@"%@",msg);
}

注意：

1、如果自定义类不实现NSCopying则无法进行持久化保存（到文件）、或错误赋值

2、如果自定义类不重写isEqual则默认使用内存地址比较两个对象，可能会出现意想不到的结果

3、isEqual和hash方法要同时重写，否则isEqual方法判断将不正确