Question

I am getting error messages in the implementation file (commented out) for Constants declared in the header file. Why is the compiler doing this?

Thanks in advance.

Header file:

#import <UIKit/UIKit.h>

#define kFilling Component 0
#define kBread Component 1

@interface BIDDoubleComponentViewController : UIViewController
<UIPickerViewDelegate, UIPickerViewDataSource>

@property (strong, nonatomic) IBOutlet  UIPickerView *doublePicker;
@property (strong, nonatomic) NSArray *fillingTypes;
@property (strong, nonatomic) NSArray *breadTypes;

- (IBAction) buttonPressed;


@end

Implementation file:

#import "BIDDoubleComponentViewController.h"


@implementation BIDDoubleComponentViewController

- (IBAction)buttonPressed
{
    NSInteger fillingRow = [self.doublePicker selectedRowInComponent:kFillingComponent]; // Use of undeclared identifieer 'kFillingComponent'
    NSInteger breadRow = [self.doublePicker selectedRowInComponent:kBreadComponent]; // Use of undeclared identifieer 'kBreadComponent'

    NSString *filling = self.fillingTypes[fillingRow];
    NSString *bread = self.breadTypes[breadRow];

    NSString *message = [[NSString alloc] initWithFormat:@"Your %@ on %@ will be right up.", filling, bread];

   UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Thank you for your order"
                                                message:message
                                               delegate:nil
                                      cancelButtonTitle:@"Great"
                                      otherButtonTitles:nil];
    [alert show];
}

- (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 from its nib.
    self.fillingTypes = @[@"Ham", @"Turkey", @"Peanut Butter", @"Tuna salad", @"Chicken salad", @"Roast Beef", @"Vegemite"];
    self.breadTypes = @[@"White", @"Whole Wheat", @"Rye", @"Sour Dough", @"Seven-Grain"];
}

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

#pragma mark
#pragma mark Picker Data Source Methods

- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView
{
    return 2;
}

- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component
{
    if(component == kBreadComponent) // Use of undeclared identifieer 'kFillingComponent'
    {
        return [self.breadTypes count];
    } else {
        return [self.fillingTypes count];
    }
}

#pragma mark Picker Delegate Methods

- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
{
    if(component == kBreadComponent) // Use of undeclared identifieer 'kBreadComponent'

    {
        return self.breadTypes[row];
    } else {
        return self.fillingTypes[row];
    }
}


@end

Answer 1

Your defines are bad. You have

#define kBread Component 1

But you’re using kBreadComponent. What the #define is doing is it’s defining a token called kBread that evaluates during preprocessing to the tokens Component 1. You probably meant to use

#define kBreadComponent 1