通过分组将对象添加到 NSMutablearray

Question

我希望我的 NSArray sampleData 从 parse.com 数据库接收实际数据，假设如下：

self.sampleData = @[ @{ @"date": @"12/5/2014",
                        @"group": @[ @{ @"text": @"post1", @"location": @"x,y" },
                                     @{ @"text": @"post2", @"location": @"x,y" },
                                     @{ @"text": @"post3", @"location": @"x,y" },
                                     @{ @"text": @"post4", @"location": @"x,y" },
                                     @{ @"text": @"post5", @"location": @"x,y" }
                                   ]
                        },
                     @{ @"date": @"12/3/2014",
                        @"group": @[ @{ @"text": @"post6", @"location": @"x,y" },
                                     @{ @"text": @"post7", @"location": @"x,y" },
                                     @{ @"text": @"post8", @"location": @"x,y" },
                                     @{ @"text": @"post9", @"location": @"x,y" },
                                     @{ @"text": @"post10", @"location": @"x,y" }
                                   ]
                        }
                  ];

如您所见，我想按日期对文本和位置进行分组，以便我可以将它们显示在一个视图中，其中日期作为标题，文本/位置作为内容。 以下是我目前能做的：

PFQuery *postQuery = [PFQuery queryWithClassName:kPAWParsePostsClassKey];
[postQuery whereKey:kPAWParseUserKey equalTo:[PFUser currentUser]];

postQuery.cachePolicy = kPFCachePolicyNetworkElseCache;
postQuery.limit = 20;

[postQuery findObjectsInBackgroundWithBlock:^(NSArray *myPosts, NSError *error)
 {
     if( !error )
     {

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

         NSMutableArray *objectArray = [NSMutableArray new];

         for (PFObject *object in myPosts) {
             [objectArray addObject:@{@"createdAt": [formatter stringFromDate:object.createdAt], @"text": [object objectForKey:@"text"], @"location": [object objectForKey:@"location"]}];
         }

         self.sampleData = objectArray;
         NSLog(@"My sampleData --> %@", self.sampleData);

     }
 }
];

上面的代码很明显没有任何分组，所以这里真的需要帮助。

Answer 1

好的，所以您有一个项目数组，并且您希望根据特定键将它们分组到部分中。

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

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

[myPosts enumerateObjectsUsingBlock:^(PFObject *object, NSUInteger idx, BOOL *stop) {

    NSString *dateString = [formatter stringFromDate:[object createdAt]];

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

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

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

// Sort Dictionary Keys by Date
NSArray *unsortedSectionTitles = [daysWithPosts allKeys];
NSArray *sortedSectionTitles = [unsortedSectionTitles sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
    NSDate *date1 = [formatter dateFromString:obj1];
    NSDate *date2 = [formatter dateFromString:obj2];
    return [date2 compare:date1];
}];

NSMutableArray *sortedData = [NSMutableArray arrayWithCapacity:sortedSectionTitles.count];

// Put Data into correct format:
[sortedSectionTitles enumerateObjectsUsingBlock:^(NSString *dateString, NSUInteger idx, BOOL *stop) {
    NSArray *group = daysWithPosts[dateString];
    NSDictionary *dictionary = @{ @"date":dateString,
                                  @"group":group };
    [sortedData addObject:dictionary];
}];

self.sampleData = sortedData;

此代码不会完全生成您要求的内容。它将生成如下所示的内容：

sampleData = @[ @{ @"date": @"12/5/2014",
                    @"group": @@[ PFObject*,
                                 PFObject*,
                                 PFObject*,
                                 PFObject*,
                                 PFObject*,
                               ]
                    },
                 @{ @"date": @"12/3/2014",
                    @"group": @[ PFObject*,
                                 PFObject*,
                                 PFObject*,
                                 PFObject*,
                                 PFObject
                               ]
                    }
              ];

无需将 myPosts 数组中的 PFObject* 转换为 @{ @"text": @"post5", @"location": @"x,y" }，因为您将无法访问其他信息。以下是您将如何使用此 sampleData 数组。

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView; {
    return self.sampleData.count;
}

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section; {
    return self.sampleData[section][@"date"];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section; {
    return self.sampleData[section][@"group"].count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath; {

    PFObject *post = self.sampleData[indexPath.section][@"group"][indexPath.row];
    UITableViewCell *cell = // dequeue A reusable tableviewcell here

    // configure the cell here

    return cell;
}