Question

UPDATE

It turns out that I was calling a class method on an instance of that class.

I’ve fixed that line of code to be:

double result = [CalculatorBrain runProgram:[self.brain program] usingVariableValues:[self variableValues]];

But when I run the program and that line is evaluated, I get the following error:

+[CalculatorBrain runProgram:usingVariableValues:]: unrecognized selector sent to class 0x6908

ORIGINAL

Why am I getting the following error in XCode inside of the view’s enterPressed: No visible @interface for ‘CalculatorBrain’ declares the selector ‘runProgram:usingVariableValues:’ ?

** CalculatorViewController.m **

#import "CalculatorViewController.h"
#import "CalculatorBrain.h"

@interface CalculatorViewController()

@property (nonatomic, strong) CalculatorBrain *brain;
@property (nonatomic, strong) NSMutableDictionary *variableValues;

@end

@implementation CalculatorViewController

@synthesize brain = _brain;
@synthesize variableValues = _variableValues;

- (CalculatorBrain *)brain {
    if (!_brain) _brain = [[CalculatorBrain alloc] init];
    return _brain;
}

- (NSMutableDictionary *)variableValues {
    if (!_variableValues) {
        _variableValues = [[NSMutableDictionary alloc] init];
    }
    return _variableValues;
}

- (IBAction)enterPressed {

    double *result = [self.brain runProgram:[self.brain program] usingVariableValues:[self variableValues]];

}

** CalculatorBrain.h **

#import <UIKit/UIKit.h>

@interface CalculatorBrain : NSObject

+ (double)runProgram:(id)program usingVariableValues:(NSDictionary *)variableValues;

@property (readonly) id program;


@end

Answer 1

In CalculatorBrain.h, you’re declaring a class method instead of an instance method:

+ (double)runProgram:(id)program usingVariableValues:(NSDictionary *)variableValues;

Use - instead of +.

Or, if you intend this to be a class method, call it as such:

 double *result = [CalculatorBrain runProgram:[self.brain program] usingVariableValues:[self variableValues]];