iOS Simulator generates an error when I press any digit button in my calculator

Question

Hello!

I have a trouble in 21.2 exercise. In that exercise I build Fraction calculator. I have 9 buttons and math actions. When I press any digit (either 1,2,3 or any else) on iOS Simulator it generates an error:

    2012-08-05 15:09:05.026 Fraction_Calculator[834:f803] -[ViewController digit5]: unrecognized selector sent to instance 0x6843e00
2012-08-05 15:09:05.029 Fraction_Calculator[834:f803] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ViewController digit5]: unrecognized selector sent to instance 0x6843e00'
*** First throw call stack:
(0x14b5022 0xeb5cd6 0x14b6cbd 0x141bed0 0x141bcb2 0x14b6e99 0x1b14e 0x1b0e6 0xc1ade 0xc1fa7 0xc1266 0x403c0 0x405e6 0x26dc4 0x1a634 0x139fef5 0x1489195 0x13edff2 0x13ec8da 0x13ebd84 0x13ebc9b 0x139e7d8 0x139e88a 0x18626 0x28ad 0x2815)
terminate called throwing an exception

What that means: " unrecognized selector sent to instance 0x6843e00 " and " '-[ViewController digit5]: unrecognized selector sent to instance 0x6843e00' ".

Here is my code of that program:

ViewController.h

Code: Objective-C

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

@interface ViewController : UIViewController

@property (strong, nonatomic) IBOutlet UILabel *display;

-(void) processDigit: (int) digit;
-(void) processOp: (char) theOp;
-(void) storeFracPart;

-(IBAction) clickDigit: (UIButton *) sender;

-(IBAction) clickPlus;
-(IBAction) clickMinus;
-(IBAction) clickMultiply;
-(IBAction) clickDivide;

-(IBAction) clickOver;
-(IBAction) clickEquals;
-(IBAction) clickClear;

@end

ViewController.m

Code: Objective-C

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController
{
    char                op;
    int                 currentNumber;
    BOOL                firstOperand, isNumerator;
    Calculator          *myCalculator;
    NSMutableString     *displayString;
}

@synthesize display;

-(void) processDigit:(int)digit
{
    currentNumber=currentNumber*10+digit;

    [displayString appendString:[NSString stringWithFormat:@"%i", digit]];
    display.text=displayString;
}

-(IBAction) clickDigit:(UIButton *)sender
{
    int digit=sender.tag;

    [self processDigit: digit];
}

-(void) processOp: (char) theOp
{
    NSString *opStr;

    op=theOp;

    switch(theOp)
    {
            case '+':
                opStr=@"+";
                break;
            case '-':
                opStr=@"-";
                break;
            case '*':
                opStr=@"*";
                break;
            case '/':
                opStr=@"/";
                break;
    }

    [self storeFracPart];
    firstOperand=NO;
    isNumerator=YES;

    [displayString appendString: opStr];
    display.text=displayString;
}

-(void) storeFracPart
{
    if(firstOperand)
    {
       if(isNumerator)
       {
           myCalculator.operand1.numerator=currentNumber;
           myCalculator.operand1.denominator=1;
       }
        else
            myCalculator.operand1.denominator=currentNumber;
    }
    else if (isNumerator)
    {
        myCalculator.operand2.numerator=currentNumber;
        myCalculator.operand2.denominator=1;
    }
    else
    {
        myCalculator.operand2.denominator=currentNumber;
        firstOperand=YES;
    }
currentNumber=0;
}

-(IBAction) clickOver
{
    [self storeFracPart];
    isNumerator=NO;
    [displayString appendString: @"/"];
    display.text=displayString;
}

-(IBAction) clickPlus
{
    [self processOp: '+'];
}

-(IBAction) clickMinus
{
    [self processOp: '-'];
}

-(IBAction) clickMultiply
{
    [self processOp: '*'];
}

-(IBAction) clickDivide
{
    [self processOp: '/'];
}

-(IBAction) clickEquals
{
    if (firstOperand==NO)
    {
        [self storeFracPart];
        [myCalculator performOperation: op];

        [displayString appendString: @"="];
        [displayString appendString: [myCalculator.accumulator convertToString]];
        display.text=displayString;

        currentNumber=0;
        isNumerator=YES;
        firstOperand=YES;
        [displayString setString: @""];        
    }
}

-(IBAction) clickClear
{
    isNumerator=YES;
    firstOperand=YES;
    currentNumber=0;
    [myCalculator clear];

    [displayString setString:@""];
    display.text=displayString;
}

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

    firstOperand=YES;
    isNumerator=YES;
    displayString=[NSMutableString stringWithCapacity:40];
    myCalculator=[[Calculator alloc]init];
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

@end

Thanks a lot!

Answer 1

The error message means that the code is attempting to call method digit5 on an object that does not have a method called digit5 . If this is a method that your button is calling, you need to define it in your view controller class, presumably along with digit0 .. digit9 methods.

Having ten methods may be suboptimal, though: a better approach would be to tag the buttons with tags corresponding to their respective digits, use the same method for all digit buttons, and harvest the tag inside the invocation.

tag is an NSInteger property of UIView , defined as follows:

@property(nonatomic) NSInteger tag