NSDate没有时间for循环中的条件语句

Question

下面是我的部分代码：

[postQuery findObjectsInBackgroundWithBlock:^(NSArray *myPosts, NSError *error)
 {
     if( !error )
     {
         NSMutableArray *resultArray = [NSMutableArray new];
         NSArray *createdAtGroup = [myPosts valueForKeyPath:@"@distinctUnionOfObjects.createdAt"];

         NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
         [formatter setDateFormat:@"MM/dd/yyyy"];

         NSCalendar *calendar = [NSCalendar currentCalendar];
         NSDateComponents *comps = [calendar components:(NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit)
                                               fromDate:[NSDate date]];
         NSDate *createdAt = [calendar dateFromComponents:comps];

        for (createdAt in createdAtGroup)
        {
            NSLog(@"createdAt ------> %@", createdAt);

            NSMutableDictionary *entry = [NSMutableDictionary new];
            [entry setObject:[formatter stringFromDate:createdAt] forKey:@"createdAt"];

            NSArray *createdAtSections = [myPosts filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"createdAt = %@", createdAt]];
            //NSArray *createdAtSections = [myPosts filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"createdAt = %@", [formatter stringFromDate:createdAt]]];

            for (int i=0; i < createdAtSections.count; i++) {
                NSString *text = [[createdAtSections objectAtIndex:i] objectForKey:@"text"];
                [entry setObject:text forKey:@"text"];

            }
            [resultArray addObject:entry];
        }
         NSLog(@"%@", resultArray);

     }
 }
];

查看 For 循环中的条件语句：

for (createdAt in createdAtGroup)

我希望 createdAt 立即声明为 NSDate，以便我可以将 text 分组到同一日期。正如我所搜索的，似乎没有办法从 NSDate 中提取时间。但是，我发现了他们声称可以做到这一点的这段代码，但它对我不起作用。

 NSCalendar *calendar = [NSCalendar currentCalendar];
         NSDateComponents *comps = [calendar components:(NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit)
                                               fromDate:[NSDate date]];
         NSDate *createdAt = [calendar dateFromComponents:comps];

有谁知道我是否错过了这里的任何内容或任何其他方式来实现这一目标？谢谢。

这里我也给出我的输出：

• 2014-12-08 00:00:56.218 createdAt ------> 2014-10-14 13:45:39 +0000
• 2014-12-08 00:00:56.224 createdAt ------> 2014-10-14 13:51:18 +0000
• 2014-12-08 00:00:56.231 createdAt ------> 2014-09-04 09:56:27 +0000
• 2014-12-08 00:00:56.233 createdAt ------> 2014-09-16 05:28:57 +0000
• 2014-12-08 00:00:56.235 createdAt ------> 2014-10-23 07:34:15 +0000
• 2014-12-08 00:00:56.237 createdAt ------> 2014-09-12 03:04:50 +0000
• 2014-12-08 00:00:56.239 createdAt ------> 2014-09-16 05:12:59 +0000
• 2014-12-08 00:00:56.246 createdAt ------> 2014-09-16 08:05:54 +0000
• 2014-12-08 00:00:56.248 createdAt ------> 2014-09-10 06:01:19 +0000
• 2014-12-08 00:00:56.250 createdAt ------> 2014-09-10 07:17:09 +0000
• 2014-12-08 00:00:56.254 ( { createdAt = "10/14/2014"; text = "www.thecubeinn.com.tw"; }, { createdAt = "10/14/2014"; text = "www.thecubeinn.com.tw"; }, { createdAt = "09/04/2014"; text = "梅花湖"; }, { createdAt = "09/16/2014"; 文字=南庄； }, { createdAt = "2014 年 10 月 23 日"; text = "家乐福，内湖"; }, { createdAt = "09/12/2014"; text = "元吉早午餐"; }, { createdAt = "09/16/2014"; text = "这里的食物出奇的好"; }, { createdAt = "09/16/2014"; text = "新州南寮港"; }, { createdAt = "09/10/2014"; text = "雅娜的家"; }, { createdAt = "09/10/2014"; text = "王龙佩"; } )

Answer 1

好的，所以您要做的是循环浏览所有项目，并将它们放入按天标记的存储桶中（NSDictionary 在这里工作得很好 - NSNumber 甚至可以作为键进行散列）。

// Get the calendar for the user's locale
NSCalendar *calendar = [NSCalendar currentCalendar];

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
     [formatter setDateFormat:@"MM/dd/yyyy"];

// Sparse dictionary, containing keys for "days with posts"
NSMutableDictionary *daysWithPosts = [NSMutableDictionary dictionary];

[myPosts enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {

    // use this if 'createdAt' is a UTC time-stamp
    // NSDate *date = [NSDate dateWithTimeIntervalSince1970:[obj createdAt].floatValue];
    // NSNumber *uniqueDay = @([calendar ordinalityOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitEra forDate:date]); // This is not fast

    NSString *dateString = [formatter stringFromDate:[obj createdAt]]; // EDIT 1

    // Check to see if we have a day already.
    NSMutableArray *posts = [daysWithPosts objectForKey: dateString /*uniqueDay*/];

    // If not, create it
    if (posts == nil || (id)posts == [NSNull null])
    {
        posts = [NSMutableArray arrayWithCapacity:1];
        [daysWithPosts setObject:posts forKey: dateString /*uniqueDay*/];
    }

    // add post to day
    [posts addObject:obj];
}];

// Sections array for TableView
NSArray *sectionTitles = [daysWithPosts allKeys]; // keep this around to re-format to strings?
NSArray *sections = [daysWithPosts allValues];

结果是您可以在 Tableview 中使用的部分和标题数组。

id rowData = sections[indexPath.section][indexPath.row];

您可能还想根据各自的时间进一步对各个天进行排序。

[sections enumeratObjectsUsingBlock:^(id obj, NSUinteger idx, BOOL *stop) {
    [(NSMutableArray*)obj sortUsingDescriptors:@[NSSortDescriptor sortDescriptorWithKey:@"createdAt" ascending:YES]];
}];