How should I ideally create a well-structured UITableViewDataSource?

Question

I have an NSArray of songs fetched from a server. That is my raw data source. The array contains custom objects which have an NSDictionary and NSArray as backend.

I am wondering if implementing a formatted data source using an NSDictionary will be wise. The dictionary will have section headers as keys, and the value of a certain key will have an NSArray containing the rows for that section.

I will be iterating through my raw data source and arranging it alphabetically into the dictionary.

I have a feeling that this is not a solid implementation and is very expensive. Is there any other, more solid implementation than this?

Answer 1

For small tables, rather than NSDictionary, I generally use NSArray, since dictionaries don't preserve order (and you probably don't want to continually re-sort). So I usually have an array of sections, for which I have for each section entry, at the very least, a section title and an array of rows. My array of rows has, that information that I need to present a given row (e.g. the text of the row, etc.).

The individual row and section objects, you can implement those as a NSDictionary objects themselves (and sometimes when parsing the data from JSON or XML, that's easiest), but I generally define my own Row and Section objects, e.g.:

@interface Row : NSObject

@property (nonatomic, strong) NSString *title;
@property (nonatomic, strong) NSString *subtitle;

@end

and

@interface Section : NSObject

@property (nonatomic, strong) NSString *title;
@property (nonatomic, strong) NSMutableArray *rows;

@end

Then my table view controller has an NSArray for the sections:

@property (nonatomic, strong) NSMutableArray *sections;

And I populate it like so:

self.sections = [NSMutableArray array];

Section *sectionObject;

sectionObject = [[Section alloc] initWithTitle:@"Marx Brothers" rows:nil];
[sectionObject.rows addObject:[[Row alloc] initWithTitle:@"Chico"   subtitle:@"Leonard Marx"]];
[sectionObject.rows addObject:[[Row alloc] initWithTitle:@"Harpo"   subtitle:@"Adolph Marx"]];
[sectionObject.rows addObject:[[Row alloc] initWithTitle:@"Groucho" subtitle:@"Julius Henry Marx"]];
[sectionObject.rows addObject:[[Row alloc] initWithTitle:@"Zeppo"   subtitle:@"Herbert Manfred Marx"]];
[self.sections addObject:sectionObject];

sectionObject = [[Section alloc] initWithTitle:@"Three Stooges" rows:nil];
[sectionObject.rows addObject:[[Row alloc] initWithTitle:@"Moe"   subtitle:@"Moses Harry Horwitz"]];
[sectionObject.rows addObject:[[Row alloc] initWithTitle:@"Larry" subtitle:@"Louis Feinberg"]];
[sectionObject.rows addObject:[[Row alloc] initWithTitle:@"Curly" subtitle:@"Jerome Lester \"Jerry\" Horwitz"]];
[self.sections addObject:sectionObject];

And then I have the typical UITableViewDataSource methods:

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

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    Section *sectionObject = self.sections[section];
    return [sectionObject.rows count];
}

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
{
    Section *sectionObject = self.sections[section];
    return sectionObject.title;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"Cell"];

    Section *sectionObject = self.sections[indexPath.section];
    Row *rowObject = sectionObject.rows[indexPath.row];

    cell.textLabel.text = rowObject.title;
    cell.detailTextLabel.text = rowObject.subtitle;

    return cell;
}

For bigger, database data driven tables, I might not keep the data in arrays, but rather use Core Data or SQLite, but the idea is the same. Make sure I have Section and Row classes that keep my table view controller code self-explanatory and insulated from the details of the data implementation.