Question

HERE IS THE CODE: http://min.us/mWdMO0n14

I’m a Obj C newbie, so I’ve searched quite a bit, but haven’t found anything that can solve my problem.

I have CalculatorViewController.h and .m and then CalculatorBrain.h and.m (Stanford Lectures)

in CalculatorBrain.m, I have the following method, with all of the variables defined as private in the CalculatorBrain header.

- (void)clearEverythingOnShakeGesture{
    operand = 0;
    waitingOperation = @"";
    waitingOperand = 0;
}

Then in CalculatorBrain.m , I have everything set up to detect shakes, as follows. I’ve included some of the code above the shake detection just so you have a general idea.

@interface CalculatorViewController()
@property(nonatomic, retain) CalculatorBrain *brain;
@end

@implementation CalculatorViewController

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

-(BOOL)canBecomeFirstResponder{
    return YES;
}

-(void)viewDidAppear: (BOOL) animated{
    [super viewDidAppear:animated];
    [self becomeFirstResponder]; 
}

- (void)motionBegan:(UIEventSubtype)motion withEvent:(UIEvent *)event {
    if (event.subtype == UIEventSubtypeMotionShake)
    {
        NSLog(@"SHAKE IT!");
        [brain clearEverythingOnShakeGesture]; //********** not sure how to call this.

    }
}

I’m not sure how to call [brain clearEverythingOnShakeGesture]; , because I get the error “Class method +clearEverythingOnShakeGesture not found, defaults to return type id”. However, if I make it a class method, the variables inside are instance variables, which provides another error. Any help greatly appreciated.

Answer 1

The project’s AppDelegate posted in the comment above is building the calculator view controller from a nib, then releasing it immediately. The app functions partially, but the UILabel property to be cleared on the shake gesture is nulled at that point.

Also, it’s a good practice to declare private properties in the private category, synthesize them with _underscore aliases, and refer to them as self.property outside of synthesized methods.