Grouping in TableView

Question

There is an array of objects (Zakazchik):

@property (strong, nonatomic) NSMutableArray *zakazchikFavoritesArray;

Each object has field @property int zakazchikCategory and can vary from 1 to 23 inclusive.

How can I create a TableView, so grouping it was on this field?

ADDED:

in viewDidLoad (after filling zakazchikFavoritesArray):

dataDictionary = [NSMutableDictionary dictionary];

for (Zakazchik *object in zakazchikFavoritesArray) {
    NSMutableArray *categoryArray = dataDictionary[@(object.zakazchikCategory)];
    if (categoryArray == nil) {
        categoryArray = [NSMutableArray array];
        dataDictionary[@(object.zakazchikCategory)] = categoryArray;
    }
    [categoryArray addObject:object];
}

also:

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


-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    NSArray *array = dataDictionary[@(section)];
    return array.count;
}


-(UITableViewCell*)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
Zakazchik *object = dataDictionary[@(indexPath.section)][@(indexPath.row)];

static NSString *CellIdentifier = @"ZakazchikCellFavorites";
ZakazchikCellFavorites *customCell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

customCell.zakazchikName.text = object.zakazchikName;

return customCell;
}


-(NSString*)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
{
Zakazchik *object = dataDictionary[@(section)];

return [NSString stringWithFormat:@"%i", object.zakazchikCategory];
}

i got error:

2015-05-30 myApp[12521:484566] -[__NSArrayM zakazchikCategory]: unrecognized selector sent to instance 0x7b735f00
2015-05-30 myApp[12521:484566] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayM zakazchikCategory]: unrecognized selector sent to instance 0x7b735f00'

Answer 1

The most straightforward way to do this is to first organize your data in to a new data structure that sorts them by the category property. I would recommend using a dictionary that maps from category to an array of all objects that have that category value. You can transform your data like this:

NSMutableDictionary *dataDictionary = [NSMutableDictionary dictionary];

for (Zakazchik *object in zArray) {
    NSMutableArray *categoryArray = dataDictionary[@(object.category)];
    if (categoryArray == nil) {
        categoryArray = [NSMutableArray array];
        dataDictionary[@(object.zakazchikCategory)] = categoryArray;
    }
    [categoryArray addObject:object];
}

Then use this data structure when implementing your UITableView data source methods:

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

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    NSArray *array = dataDictionary[@(section)];
    return array.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView
         cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    Zakazchik *object = dataDictionary[@(indexPath.section)][@(indexPath.row)];

   // Create your cell using the object..
}

- (NSString*)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
    NSArray *array = dataDictionary[@(section)];
    Zakazchik *firstObject = [array firstObject];

    return [NSString stringWithFormat:@"%i", firstObject.zakazchikCategory];
}

Answer 2

To avoid error you can rewrite this method as follow

-(NSString*)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
{
   NSMutableArray *objectArray = dataDictionary[@(section)]; // not needed 
   return [NSString stringWithFormat:@"Category #%i", section];
}

Because your dataDictionary contains arrays of Zakazchik not objects directly and, I guess you have another table/array with names of categories so in this method no reason to select this object