Question

我在项目中创建了两个名为NSManagedObject和Contact的{{1}}。两个对象都有一个名为Groups的属性。我有一个包含两个对象的数组。

我希望按timeLastMessageReceived的时间顺序排列数组。

timeLastMessageReceived

我正在尝试这种方法：

@interface Contact : NSManagedObject

...

@property (nonatomic, retain) NSDate * timeLastMessageReceived;
@property (nonatomic, retain) NSString * lastMessage;

@end



@interface Groups : NSManagedObject

@property (nonatomic, retain) NSDate * timeLastMessageReceived;
@property (nonatomic, retain) NSString * lastMessage;

@end

但它因错误而崩溃： - NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init]; [dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"GMT"]]; [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"]; NSArray *newArr = [self.chatArray sortedArrayWithOptions:0 usingComparator:^NSComparisonResult(id obj1, id obj2) { NSDate *date1 = obj1[@"timeLastMessageReceived"]; NSDate *date2 = obj2[@"timeLastMessageReceived"]; return [date1 compare:date2]; }];
有任何想法吗。感谢。

Answer 1

更新回答：

作为替代方案，您可以使用排序描述符对数组进行排序：

NSSortDescriptor *timeLastMessageReceivedDescriptor = [[NSSortDescriptor alloc] initWithKey:@"timeLastMessageReceived" ascending:YES];
NSArray *sortDescriptors = @[timeLastMessageReceivedDescriptor];
NSArray *sortedArray = [self.chatArray sortedArrayUsingDescriptors:sortDescriptors];

原始回答：

我猜self.chatArray包含Contact类型的实例？您应该能够像那样实现比较器：

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"GMT"]];
[dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
NSArray *newArr = [self.chatArray sortedArrayWithOptions:0 usingComparator:^NSComparisonResult(Contact *contact1, Contact *contact2) {
    NSDate *date1 = contact1.timeLastMessageReceived;
    NSDate *date2 = contact2.timeLastMessageReceived;
    return [date1 compare:date2];
}];

Answer 2

您可以在[]的实例上使用-objectForKeyedSubscript:运算符（即NSDictionary）。正如错误消息所述，您正在处理Contact的实例，因此它不支持下标运算符。

您展示了timeLastMessageReceived仅仅是Contact上的属性的方式，因此您应该能够使用默认的属性访问语法：

    NSDate *date1 = obj1.timeLastMessageReceived;
    NSDate *date2 = obj2.timeLastMessageReceived;

Answer 3

我将创建一个由Contact和Group实现的协议，它定义timeLastMessageReceived属性。

@protocol ContactOrGroupProtocol
@property (nonatomic, retain) NSDate * timeLastMessageReceived;
@end

然后，比较器块将是：

^NSComparisonResult(id<ContactOrGroupProtocol> obj1, id<ContactOrGroupProtocol> obj2) {
    NSDate *date1 = obj1.timeLastMessageReceived;
    NSDate *date2 = obj2.timeLastMessageReceived;
    return [date1 compare:date2];
}];

Answer 4

另一种方法是在班级Groups和Contact

中实施比较方法

- (NSComparisonResult)compareLastMessageReceived:(Groups *)group {
  return [self.timeLastMessageReceived compare:group.timeLastMessageReceived];
}

- (NSComparisonResult)compareLastMessageReceived:(Contact *)contact {
  return [self.timeLastMessageReceived compare:contact.timeLastMessageReceived];
}

并致电sortedArrayUsingSelector:

NSArray *newArr = [self.chatArray sortedArrayUsingSelector:@selector(compareLastMessageReceived:)];

订购一系列对象？

4 个答案: