Question

I have an SQL DB that contains Lat and Long info. I have found my current location and been able to get the distance of each location from my current location. I can get my tableview to show this distance, but know I want to sort that tableview so the closest are listed first.

My thought is I will need to add the distance to my SQL DB data, sort that some how and then display that info back to the tableview.

My thought is I would do all of this within my TableView. Looking for guidance on how to do this and if I should be doing it in the tableview.

#import "TulsaMasterViewController.h"
#import "TulsaDetailViewController.h"
#import "Bars.h"
#import "BarDatabase.h"

@implementation TulsaMasterViewController

@synthesize barArray = _barArray;
@synthesize currentLat = _currentLat;


- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
currentLat = newLocation;

if (newLocation.horizontalAccuracy <= 100.0f) {
    [lm stopUpdatingLocation];
}

[self.tableView reloadData];
}

- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error
{
NSString *msg = [[NSString alloc]initWithString:@"Error obtaining location"];
UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"Error" message:msg delegate:nil cancelButtonTitle:@"Done" otherButtonTitles:nil];
[alert show];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return [self.barArray count];
}

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

static NSString *CellIdentifier = @"Cell";

UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
    cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];
}

//Get the object from the array.
Bars *barObj = [self.barInfo objectAtIndex:indexPath.row];

//Set the name.
cell.textLabel.text = barObj.barName;

if (currentLat == nil) {
    cell.detailTextLabel.text = [NSString stringWithFormat:@"?"];
}else
{
    cell.detailTextLabel.text = [NSString stringWithFormat:@"%.02f", cachedDist];
}

// Set up the cell
return cell;
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([[segue identifier] isEqualToString:@"ShowDetails"]) {
    TulsaDetailViewController *detailViewController = [segue destinationViewController];

    detailViewController.detailItem = [self.barArray objectAtIndex:[self.tableView indexPathForSelectedRow].row];
}
}

- (void)viewDidLoad
{
[super viewDidLoad];

self.barArray = [BarDatabase database].barInfo;

lm = [[CLLocationManager alloc] init];
lm.delegate = self;
[lm startUpdatingLocation];
}

- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];

for (Bars *barObj in barArray) {
    NSString *strLat = barObj.Lat;
    NSString *strLong = barObj.Long;
    CLLocation *barLocation = [[CLLocation alloc] initWithLatitude:[strLat doubleValue] longitude:[strLong doubleValue]];
    CLLocationDistance distance = [currentLat distanceFromLocation:barLocation]/1000;

    [barArray addObject:[NSNumber numberWithDouble:distance]];
    NSSortDescriptor *sort=[NSSortDescriptor sortDescriptorWithKey:@"cachedDist" ascending:YES];
    [barArray sortUsingDescriptors:[NSArray arrayWithObject:sort]];
}

For reference the rest of my code

Bars.h

#import <Foundation/Foundation.h>

@interface Bars : NSObject {
    NSString *barName;
    NSString *barAddress;
    NSString *Lat;
    NSString *Long;
    NSString *cachedDist;
}

@property (nonatomic, copy) NSString *barName;
@property (nonatomic, copy) NSString *barAddress;
@property (nonatomic, copy) NSString *Lat;
@property (nonatomic, copy) NSString *Long;
@property (nonatomic, copy) NSString *cachedDist;

- (id)initWithName:(NSString *)name address:(NSString *)address latitude:(NSString *)latitude longitude:(NSString *)longitude distance:(NSString *)distance;

@end

Bars.m

#import "Bars.h"

@implementation Bars

@synthesize barName = _barName;
@synthesize barAddress = _barAddress;
@synthesize Lat = _Lat;
@synthesize Long = _Long;
@synthesize cachedDist = _cachedDist;

- (id)initWithName:(NSString *)name address:(NSString *)address latitude:(NSString *)latitude longitude:(NSString *)longitude distance:(NSString *)distance;
{
if ((self = [super init])) {
    self.barName = name;
    self.barAddress = address;
    self.Lat = latitude;
    self.Long = longitude;
    self.cachedDist = distance;
}
return self;
}

@end

BarDatabase.h

#import <Foundation/Foundation.h>
#import <sqlite3.h>

@interface BarDatabase : NSObject
{
    sqlite3 *_database;
}

+ (BarDatabase *)database;
- (NSMutableArray *)barInfo;

@end

BarDatabase.m

#import "BarDatabase.h"
#import "Bars.h"

@implementation BarDatabase

static BarDatabase *_database;

+ (BarDatabase *)database {
if (_database == nil) {
    _database = [[BarDatabase alloc] init];
}
return _database;
}

- (id)init {
if ((self = [super init])) {
    NSString *sqLiteDb = [[NSBundle mainBundle] pathForResource:@"TulsaBars" 
                                                         ofType:@"sqlite"];

    if (sqlite3_open([sqLiteDb UTF8String], &_database) != SQLITE_OK) {
        NSLog(@"Failed to open database!");
    }
}
return self;
}

- (void)dealloc {
sqlite3_close(_database);
}

- (NSMutableArray *)barInfo {

NSMutableArray *retval = [[NSMutableArray alloc] init];
NSString *query = @"SELECT * FROM TulsaBars";
sqlite3_stmt *statement;
if (sqlite3_prepare_v2(_database, [query UTF8String], -1, &statement, nil) 
    == SQLITE_OK) {
    while (sqlite3_step(statement) == SQLITE_ROW) {
        char *nameChars = (char *) sqlite3_column_text(statement, 1);
        char *addressChars = (char *) sqlite3_column_text(statement, 2);
        char *latChars = (char *) sqlite3_column_text(statement, 8);
        char *longChars = (char *) sqlite3_column_text(statement, 9);
        NSString *name = [[NSString alloc] initWithUTF8String:nameChars];
        NSString *address = [[NSString alloc] initWithUTF8String:addressChars];
        NSString *latitude = [[NSString alloc] initWithUTF8String:latChars];
        NSString *longitude = [[NSString alloc] initWithUTF8String:longChars];

        Bars *info = [[Bars alloc]
                      initWithName:name address:address latitude:latitude longitude:longitude];                        
        [retval addObject:info];
    }
    sqlite3_finalize(statement);
}
return retval;

}
@end

Answer 1

Hrm. There should be no sorting happening inside cellForRowAtIndexPath. It’s too late in the game. If each cell is 1 bar, and the bars should be sorted by distance, I recommend achieving the sort in a lazy getter for your self.barInfo (if that’s your list of bars).

I’m not sure what your model looks like, but if each bar object has a property for distance from whatever your reference point is, your sorting would look similar to what you have there.

This sorting would only happen the when the first cell is loaded (that’s the “lazy” part) and then cached. So your cellForRowAtIndexPath: would just ask for the model object at it’s indexPath’s row, trusting that it is in the right order.

I’m not sure how much of this terminology you are familiar with, so feel free to ask clarifying questions and I will iterate on the answer.

EDIT after sharing more code:
I think you should add a @property to the bar called something like cachedDistance, and whenever you come onscreen (viewWillAppear), iterate over the bars and set their cached distance (using similar code to what you have in cellForRow…). Then implement a getter for self.barArray: -(NSArray *)barArray which essentially returns the barArray sorted using a sortDescriptor with the name of your cached distance property as it’s key. This will simplify your cellForRow… code a lot.

You can then extend the logic to recalculate the distances when you get location updates, perhaps only if it is a certain distance from the previous.