Calling a class method from a View gives: "Unrecognized selector sent to class"

Question

I'm trying to call a class method that is defined in an imported header file.

When I run the code below, I get this error in the View on the "double *result = ..." line:

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

** 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 = [CalculatorBrain 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

** CalculatorBrain.m **

#import "CalculatorBrain.h"

@interface CalculatorBrain()
    @property (nonatomic, strong) NSMutableArray *programStack;
@end

@implementation CalculatorBrain

@synthesize programStack = _programStack;


... other code ...

+ (double)runProgram:(id)program :(NSDictionary *) usingVariableValues 
{

    NSLog(@"variableValues is %@", usingVariableValues);

    NSMutableArray *stack;

    if ([program isKindOfClass:[NSArray class]]) {

        stack = [program mutableCopy];

        NSLog(@"runProgram");

        // if vars are passed in
        if ([usingVariableValues isKindOfClass:[NSDictionary class]]) {

            NSLog(@"vars are passed in: %@", usingVariableValues);

            id obj;
            int index = 0;

            NSEnumerator *enumerator = [program objectEnumerator];

            // for every obj in programStack
            while ((obj = [enumerator nextObject])) {

                id varVal = [usingVariableValues objectForKey:(obj)];

                // test
                NSLog(@"usingVariableValues objectForKey:(obj) is %@", varVal);

                // if the obj is a variable key
                if (!varVal) {
                    varVal = 0;

                    NSLog(@"varVal is false");
                }

                NSLog(@"Replacing object at index %@ of stack with var %@", index, varVal);


                // replace the variable with value from usingVariableValues OR 0
                [stack replaceObjectAtIndex:(index) withObject:varVal];

                index += 1;

            }
        }

    }

    return [self popOperandOffStack:stack];
}

Answer 1

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

Is defined as a class method, but you call it as an object method

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

To call it on the class do:

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

Or

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

---

You changed your code, indicating, that the method is still not found. Did you implement it?

---

If it is implemented, then you might have to add the implementation file (aka .m) to the target in Xcode.

By the way,: probably you want your method to return a double not a double*, a pointer to a double.

---

your header has a signature:

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

While your implementation has

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

They are not identical:

1. The header promisses a pointer to a double to be returned. You don't want that.

2. They don't even have the same name +runProgram:usingVariableValues: vs +runProgram::