populate uipicker view with results from core data DB using an NSArray

Question

I am trying to populate a UIPickerView with the results of a NSFetchRequest. The results of the NSFetchRequest are then stored in an NSArray. I am using Core Data to interact with the SQLite DB. I have a simple class file that contains a UIPickerView that is associated with a storyboard scene in my project.

The header file for the class looks like the following,

ViewControllerUsers.h

#import <UIKit/UIKit.h>
#import "AppDelegate.h"

@interface ViewControllerUsers : UIViewController <NSFetchedResultsControllerDelegate, UIPickerViewDelegate, UIPickerViewDataSource>
{

NSArray *dictionaries;
}
@property (nonatomic, strong) NSFetchedResultsController *fetchedResultsController;
// Core Data
@property (strong, nonatomic) NSManagedObjectContext *managedObjectContext;

@property (nonatomic, strong) NSArray *users;

@property (strong, nonatomic) IBOutlet UIPickerView *uiPickerViewUsers;

@property (weak, nonatomic) IBOutlet UIBarButtonItem *btnDone;

@property (weak, nonatomic) IBOutlet UIButton *btnChangePin;

// added for testing purposes
@property (nonatomic, strong) NSArray *usernames;

- (IBAction)dismissScene:(id)sender;

- (IBAction)changePin:(id)sender;

@end

The implementation file looks like the following,

ViewControllerUsers.m

#import "ViewControllerUsers.h"

@interface ViewControllerUsers ()

@end

@implementation ViewControllerUsers

// Core Data
@synthesize managedObjectContext = _managedObjectContext;

@synthesize uiPickerViewUsers = _uiPickerViewUsers;

@synthesize usernames = _usernames;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.

    // Core Data
    if (_managedObjectContext == nil)
    {
        _managedObjectContext = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
        NSLog(@"After _managedObjectContext: %@",  _managedObjectContext);
    }

    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Account"];

    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Account" inManagedObjectContext:_managedObjectContext];
    request.resultType = NSDictionaryResultType;
    request.propertiesToFetch = [NSArray arrayWithObject:[[entity propertiesByName] objectForKey:@"username"]];
    request.returnsDistinctResults = YES;

    _usernames = [_managedObjectContext executeFetchRequest:request error:nil];

    NSLog (@"names: %@",_usernames);
}


-(NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView
{
    //One column
    return 1;
}

-(NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component
{
    //set number of rows
    return _usernames.count;
}

-(NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
{
    //set item per row
    return [_usernames objectAtIndex:row];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (void)viewDidUnload {
    [self setBtnDone:nil];
    [self setUiPickerViewUsers:nil];
    [self setBtnChangePin:nil];
    [super viewDidUnload];
}
- (IBAction)dismissScene:(id)sender {

    [self dismissModalViewControllerAnimated:YES];
}

- (IBAction)changePin:(id)sender {
}
@end

The current code is causing the app to crash, but the NSLog is show the results of the NSFetchRequest in the NSArray. I currently think that I am not formatting the results of the NSFetchRequest in the NSArray properly if I had to take a guess.

The crash log looks like the following,

2013-06-26 16:49:24.219 KegCop[41233:c07] names: ( { username = blah; }, { username = chris; }, { username = root; } ) 2013-06-26 16:49:24.223 KegCop[41233:c07] -[NSKnownKeysDictionary1 isEqualToString:]: unrecognized selector sent to instance 0xe54d9a0 2013-06-26 16:49:24.223 KegCop[41233:c07] Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSKnownKeysDictionary1 isEqualToString:]: unrecognized selector sent to instance 0xe54d9a0' First throw call stack:

Answer 1

Your usernames array is an array of dictionaries, not an array of strings.

Update your titleForRow: method like this:

-(NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
{
    //set item per row
    return _usernames[row][@"username"];
}