iPhone Core Data “Production” Error Handling

Question

I\'ve seen in the example code supplied by Apple references to how you should handle Core Data errors. I.e:

NSError *error = nil;
if (![context save:&err         


        

Answer 1

This is one generic method I came up with to handle and display validation errors on the iPhone. But Marcus is right: You'd probably want to tweak the messages to be more user friendly. But this at least gives you a starting point to see what field didn't validate and why.

- (void)displayValidationError:(NSError *)anError {
    if (anError && [[anError domain] isEqualToString:@"NSCocoaErrorDomain"]) {
        NSArray *errors = nil;

        // multiple errors?
        if ([anError code] == NSValidationMultipleErrorsError) {
            errors = [[anError userInfo] objectForKey:NSDetailedErrorsKey];
        } else {
            errors = [NSArray arrayWithObject:anError];
        }

        if (errors && [errors count] > 0) {
            NSString *messages = @"Reason(s):\n";

            for (NSError * error in errors) {
                NSString *entityName = [[[[error userInfo] objectForKey:@"NSValidationErrorObject"] entity] name];
                NSString *attributeName = [[error userInfo] objectForKey:@"NSValidationErrorKey"];
                NSString *msg;
                switch ([error code]) {
                    case NSManagedObjectValidationError:
                        msg = @"Generic validation error.";
                        break;
                    case NSValidationMissingMandatoryPropertyError:
                        msg = [NSString stringWithFormat:@"The attribute '%@' mustn't be empty.", attributeName];
                        break;
                    case NSValidationRelationshipLacksMinimumCountError:  
                        msg = [NSString stringWithFormat:@"The relationship '%@' doesn't have enough entries.", attributeName];
                        break;
                    case NSValidationRelationshipExceedsMaximumCountError:
                        msg = [NSString stringWithFormat:@"The relationship '%@' has too many entries.", attributeName];
                        break;
                    case NSValidationRelationshipDeniedDeleteError:
                        msg = [NSString stringWithFormat:@"To delete, the relationship '%@' must be empty.", attributeName];
                        break;
                    case NSValidationNumberTooLargeError:                 
                        msg = [NSString stringWithFormat:@"The number of the attribute '%@' is too large.", attributeName];
                        break;
                    case NSValidationNumberTooSmallError:                 
                        msg = [NSString stringWithFormat:@"The number of the attribute '%@' is too small.", attributeName];
                        break;
                    case NSValidationDateTooLateError:                    
                        msg = [NSString stringWithFormat:@"The date of the attribute '%@' is too late.", attributeName];
                        break;
                    case NSValidationDateTooSoonError:                    
                        msg = [NSString stringWithFormat:@"The date of the attribute '%@' is too soon.", attributeName];
                        break;
                    case NSValidationInvalidDateError:                    
                        msg = [NSString stringWithFormat:@"The date of the attribute '%@' is invalid.", attributeName];
                        break;
                    case NSValidationStringTooLongError:      
                        msg = [NSString stringWithFormat:@"The text of the attribute '%@' is too long.", attributeName];
                        break;
                    case NSValidationStringTooShortError:                 
                        msg = [NSString stringWithFormat:@"The text of the attribute '%@' is too short.", attributeName];
                        break;
                    case NSValidationStringPatternMatchingError:          
                        msg = [NSString stringWithFormat:@"The text of the attribute '%@' doesn't match the required pattern.", attributeName];
                        break;
                    default:
                        msg = [NSString stringWithFormat:@"Unknown error (code %i).", [error code]];
                        break;
                }

                messages = [messages stringByAppendingFormat:@"%@%@%@\n", (entityName?:@""),(entityName?@": ":@""),msg];
            }
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Validation Error" 
                                                            message:messages
                                                           delegate:nil 
                                                  cancelButtonTitle:nil otherButtonTitles:@"OK", nil];
            [alert show];
            [alert release];
        }
    }
}

Enjoy.