UITableView grouping sections from NSMutableArray

Question

I have an app that basically reads an xml file and displays the results in a UITableView. I am trying to group the list items by "country" (an attribute of the xml file elements) and display them in UITableView Sections.

Currently i read the xml file and store each Element as a custom object in an NSMutableArray. The array has the following structure:

Array: 0 => (title, description, date, country) 1 => (title, description, date, country) 2 => (title, description, date, country) 3 => (title, description, date, country)

I have tried creating another array of unique countries which has allowed me to create the section headers correctly but i am struggling to work out a way to display the correct items beneath each section header.

if(![countryArray containsObject:itemCountry]) //if country not already in array
{
   [countryArray addObject:itemCountry]; //Add NSString of country name to array
}

Where itemCountry is the country attribute of each element as i loop through the xml file.

[countryArray count]; //gives me the amount of sections needed

So i guess my question is how do i work out how many rows need to go in each section? How do display the correct array items for each section?

Any help or pointers would be great

Answer 1

Rather than creating an array of custom objects containing your data, you should look at creating a dictionary.

NSMutableDictionary * theDictionary = [NSMutableDictionary dictionary];

// Here `customObjects` is an `NSArray` of your custom objects from the XML
for ( CustomObject * object in customObjects ) {   
    NSMutableArray * theMutableArray = [theDictionary objectForKey:object.country];
    if ( theMutableArray == nil ) {
        theMutableArray = [NSMutableArray array];
        [theDictionary setObject:theMutableArray forKey:object.country];
    } 

    [theMutableArray addObject:object];
}

/* `sortedCountries` is an instance variable */
self.sortedCountries = [[theDictionary allKeys] sortedArrayUsingSelector:@selector(localizedCaseInsensitiveCompare:)];

/* Save `theDictionary` in an instance variable */
self.theSource = theDictionary;

Later in numberOfSectionsInTableView:

- (NSInteger)numberOfSectionsInTableView {
    return [self.sortedCountries count];
}

In tableView:numberOfRowsInSection::

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return [[self.theSource objectForKey:[self.sortedCountries objectAtIndex:section]] count];
}

In tableView:cellForRowAtIndexPath::

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    [..]

    /* Get the CustomObject for the row */
    NSString * countryName = [self.sortedCountries objectAtIndex:indexPath.section];
    NSArray * objectsForCountry = [self.theSource objectForKey:countryName];
    CustomObject * object = [objectsForCountry objectAtIndex:indexPath.row];

    /* Make use of the `object` */

    [..]
}

This should take you the whole way.

Side Note
If it weren't to present the data and just get the count of the countries then a better alternative to PengOne's approach is to use an NSCountedSet.

NSCountedSet * countedSet = [NSCounted set];
for ( NSString * countryName in countryNames ) {
    [countedSet addObject:countryName];
}

Now all unique countries are available in [countedSet allObjects] and count for each country would be [countedSet countForObject:countryName].

Answer 2

For the section headers using Deepak's answer just go:

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
    return [self.sortedCountries objectAtIndex:section];
}