Question

I’m new to objective-c and I’ve gone through a tutorial to build a ‘tip calculator’ app for iPhone. I’m using Xcode 4.3.3 and I have checked all the code and it is identical to that in the tutorial (which I’m sure is correct). I have been trawling through site trying to find someone who had the same problem and I have not been able to fix it so I appreciate any help. This is the message that appears whenever I try to run the app.

2012-07-23 14:22:01.021 Tip_Calculator[554:f803] -[ViewController
initWithCoder:]: unrecognized selector sent to instance 0x68a3130
2012-07-23 14:22:01.025 Tip_Calculator[554:f803] * Terminating app
due to uncaught exception ‘NSInvalidArgumentException’, reason:
‘-[ViewController initWithCoder:]: unrecognized selector sent to
instance 0x68a3130’
* First throw call stack: (0x13c8022 0x1559cd6 0x13c9cbd 0x132eed0 0x132ecb2 0x234135 0x333c6e 0x333383 0x233cad 0x333c6e 0x33367b
0x333383 0x233105 0x43ceef 0x43d03e 0x11d7a 0x11ff8 0x1117f 0x20183
0x20c38 0x14634 0x12b2ef5 0x139c195 0x1300ff2 0x12ff8da 0x12fed84
0x12fec9b 0x10c65 0x12626 0x253d 0x24a5) terminate called throwing an
exception(lldb)

This is the area flagged in main.m:

#import <UIKit/UIKit.h>

#import "AppDelegate.h"

int main(int argc, char *argv[])
{
@autoreleasepool {        return UIApplicationMain(argc, argv, nil,     NSStringFromClass([AppDelegate class]));    }
}

I have checked all the interface connections and they are fine. I have also added an exception breakpoint and this error showed up :

2012-07-23 20:49:53.633 Tip_Calculator[2067:f803] -[ViewController
initWithCoder:]: unrecognized selector sent to instance 0x68c09c0
(lldb)

This is the error log that is shown:

Tip_Calculator`start:
0x2470:  pushl  $0
0x2472:  movl   %esp, %ebp
0x2474:  andl   $-16, %esp
0x2477:  subl   $16, %esp
0x247a:  movl   4(%ebp), %ebx
0x247d:  movl   %ebx, (%esp)
0x2480:  leal   8(%ebp), %ecx
0x2483:  movl   %ecx, 4(%esp)
0x2487:  addl   $1, %ebx
0x248a:  shll   $2, %ebx
0x248d:  addl   %ecx, %ebx
0x248f:  movl   %ebx, 8(%esp)
0x2493:  movl   (%ebx), %eax
0x2495:  addl   $4, %ebx
0x2498:  testl  %eax, %eax
0x249a:  jne    0x00002493               ; start + 35
0x249c:  movl   %ebx, 12(%esp)
0x24a0:  calll  0x000024b0               ; main at main.m:14
**0x24a5:  movl   %eax, (%esp)**
0x24a8:  calll  0x000033ca               ; exit
0x24ad:  hlt    
0x24ae:  nop    
0x24af:  nop 

I put asterisks around the flagged area. The same error is shown whether there is an exception breakpoint or not.

I am using storyboard, here is the .h file of the ViewController:

#import <UIKit/UIKit.h>

@interface ViewController : NSObject
{
//outlets
IBOutlet UITextField *billField;

IBOutlet UITextField *tipFieldTen;
IBOutlet UITextField *tipFieldFifteen;
IBOutlet UITextField *tipFieldTwenty;
IBOutlet UITextField *tipFieldCustom;
IBOutlet UITextField *totalFieldTen;
IBOutlet UITextField *totalFieldFifteen;
IBOutlet UITextField *totalFieldTwenty;
IBOutlet UITextField *totalFieldCustom;
IBOutlet UILabel *customPercentLabel;
IBOutlet UISlider *customPercentSlider;

NSString *billTotal;
}
-(IBAction)calculateTip:(id)sender;



@end

And here is the .m file:

#import "ViewController.h"

@implementation ViewController

- (void)awakeFromNib; 
{
[billField becomeFirstResponder]; //display keyboard for billField
}

-(IBAction)calculateTip:(id)sender
{
static BOOL toggle = YES;

if (toggle)
{
    toggle = NO;
    NSString *billFieldText = billField.text;

    float newTotal = [billFieldText floatValue];
    float customTipPercent = customPercentSlider.value;

    if(sender ==billField)
    {
        if (billFieldText.length <billTotal.length)
            billTotal = [NSString stringWithFormat:@"%.02f", 
                         newTotal / 10];
        else
            billTotal = [NSString stringWithFormat:@"%.02f",
                         newTotal * 10];

        billField.text = billTotal;

        newTotal = [billTotal floatValue];

        float tenTip = newTotal * 0.10;
        float fifteenTip = newTotal * 0.15;
        float twentyTip = newTotal * 0.20;

        tipFieldTen.text = [NSString stringWithFormat:@"%.02f", tenTip];
        tipFieldFifteen.text = [NSString stringWithFormat:@"%.02f", fifteenTip];
        tipFieldTwenty.text = [NSString stringWithFormat:@"%.02f", twentyTip];

        totalFieldTen.text = [NSString stringWithFormat:@"%.02f", newTotal + tenTip];
        totalFieldFifteen.text = [NSString stringWithFormat:@"%.02f", newTotal +   fifteenTip];
        totalFieldTwenty.text = [NSString stringWithFormat:@"%.02f", newTotal + twentyTip];
    }
    else if (sender == customPercentSlider)
    {
        int percentage = (int)(customTipPercent * 100);
        customPercentLabel.text = [NSString stringWithFormat:@"%i%%", percentage];
        float newSliderValue = ((float) percentage) / 100;
        customPercentSlider.value = newSliderValue;
        customTipPercent = newSliderValue;
    }
    float customTip = customTipPercent * newTotal;
    tipFieldCustom.text = [NSString stringWithFormat:@"%.02f", customTip];
    totalFieldCustom.text = [NSString stringWithFormat:@"%.02f", customTip + newTotal];
}
else
{
    toggle = YES;
}

}



@end

Any help would be much appreciated as I’m new to objective-c.

Answer 1

You have

@interface ViewController : NSObject

this should probably be:

@interface ViewController : UIViewController

Reason:

So your ViewController class is currently inheriting from NSObject, which does not implement initWithCoder. In fact, this method call is part of the NSCoding protocol, which UIViewController adopts.

Background:

The error you received is basically saying that an object of the class ViewController was sent a selector, or ‘message’, initWithCoder, but it didn’t have an implementation of that method. So there are two things you would generally do to track this down:

1) Check if you are sending that message anywhere in your code, and then whether the object that receives it is of a class that should recognise that method. You also have to consider that method being called from UIKit, etc frameworks, which makes this a bit more difficult.

2) If the above looks ok, then you have to consider that perhaps while your code assumes an object is one type, it might actually be a different one, hence this error occuring.

Consider this code:

NSArray *anArray = [[NSArray alloc] initWithObjects:@"aString", nil];
NSNumber *aNumber = [anArray objectAtIndex:0];
BOOL isEqual = [aNumber isEqualToNumber:[NSNumber numberWithInteger:42]];

This will compile without warning, but when run will cause an exception – because it assumes the object in the array is NSNumber, but in fact it is NSString:

* Terminating app due to uncaught exception ‘NSInvalidArgumentException’, reason: ‘-[__NSCFConstantString
isEqualToNumber:]: unrecognized selector sent to instance 0x6cbfc’