X Code Objective-C: 2 duplicate symbols error <p>Hey I'm fairly new to Objective C. I ran into this error when adding some new buttons to my iPhone app I have been working on. Not exactly sure where the duplicates are present. If anyone could point me in the right direction that would be great thanks!</p> <p><strong>Error:</strong> </p> <blockquote> <p>duplicate symbol _OBJC_CLASS_$_Weights in: /Users/mflood7356/Library/Developer/Xcode/DerivedData/1RMCalculator-bciansmbawnkrwasgwtkbkdpvswt/Build/Intermediates/1RMCalculator.build/Debug-iphonesimulator/1RMCalculator.build/Objects-normal/x86_64/ViewController.o /Users/mflood7356/Library/Developer/Xcode/DerivedData/1RMCalculator-bciansmbawnkrwasgwtkbkdpvswt/Build/Intermediates/1RMCalculator.build/Debug-iphonesimulator/1RMCalculator.build/Objects-normal/x86_64/Weights.o duplicate symbol _OBJC_METACLASS_$_Weights in: /Users/mflood7356/Library/Developer/Xcode/DerivedData/1RMCalculator-bciansmbawnkrwasgwtkbkdpvswt/Build/Intermediates/1RMCalculator.build/Debug-iphonesimulator/1RMCalculator.build/Objects-normal/x86_64/ViewController.o /Users/mflood7356/Library/Developer/Xcode/DerivedData/1RMCalculator-bciansmbawnkrwasgwtkbkdpvswt/Build/Intermediates/1RMCalculator.build/Debug-iphonesimulator/1RMCalculator.build/Objects-normal/x86_64/Weights.o ld: 2 duplicate symbols for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation)</p> </blockquote> <p><strong>Weights.m</strong></p> <pre><code>#import "Weights.h" @implementation Weights static Weights *instance = nil; +(Weights *)getInstance{ @synchronized(self){ if(instance==nil){ instance= [Weights new]; } } return instance; } static int totalWeight = 0; static int fortyFives = 0; static int thirtyFives = 0; static int twentyFives = 0; static int tens = 0; static int fives = 0; static int twoPointFives = 0; + (int)getTotalWeight { return totalWeight; } + (void)setTotalWeight:(int)newWeight { totalWeight = newWeight; [self computePlates]; } + (int)getFortyFives { return fortyFives; } + (void)setFortyFives:(int)newCount { fortyFives = newCount; } + (int)getThirtyFives { return thirtyFives; } + (void)setThirtyFives:(int)newCount { thirtyFives = newCount; } + (int)getTwentyFives { return twentyFives; } + (void)setTwentyFives:(int)newCount { twentyFives = newCount; } + (int)getTens { return tens; } + (void)setTens:(int)newCount { tens = newCount; } + (int)getFives { return fives; } + (void)setFives:(int)newCount { fives = newCount; } + (int)getTwoPointFives { return twoPointFives; } + (void)setTwoPointFives:(int)newCount { twoPointFives = newCount; } + (void)computePlates{ if(totalWeight &gt;= 45){ if(totalWeight == 45){ [self setFortyFives: 0]; [self setThirtyFives: 0]; [self setTwentyFives: 0]; [self setTens: 0]; [self setFives: 0]; [self setTwoPointFives: 0]; } else{ int workingWeight = totalWeight - 45; // Do 45s if(workingWeight &gt;= 90){ int plateCounter = 0; while(workingWeight &gt;= 90){ workingWeight = workingWeight - 90; plateCounter = plateCounter + 2; } NSLog(@"Number of 45s: %d", plateCounter); [self setFortyFives:plateCounter]; } else{ NSLog(@"Number of 45s: 0"); [self setFortyFives: 0]; } // Do 35s if(workingWeight &gt;= 70){ int plateCounter = 0; while(workingWeight &gt;= 70){ workingWeight = workingWeight - 70; plateCounter = plateCounter + 2; } NSLog(@"Number of 35s: %d", plateCounter); [self setThirtyFives:plateCounter]; } else{ NSLog(@"Number of 35s: 0"); [self setThirtyFives: 0]; } // Do 25s if(workingWeight &gt;= 50){ int plateCounter = 0; while(workingWeight &gt;= 50){ workingWeight = workingWeight - 50; plateCounter = plateCounter + 2; } NSLog(@"Number of 25s: %d", plateCounter); [self setTwentyFives:plateCounter]; } else{ NSLog(@"Number of 25s: 0"); [self setTwentyFives: 0]; } // Do 10s if(workingWeight &gt;= 20){ int plateCounter = 0; while(workingWeight &gt;= 20){ workingWeight = workingWeight - 20; plateCounter = plateCounter + 2; } NSLog(@"Number of 10s: %d", plateCounter); [self setTens:plateCounter]; } else{ NSLog(@"Number of 10s: 0"); [self setTens: 0]; } // Do 5s if(workingWeight &gt;= 10){ int plateCounter = 0; while(workingWeight &gt;= 10){ workingWeight = workingWeight - 10; plateCounter = plateCounter + 2; } NSLog(@"Number of 5s: %d", plateCounter); [self setFives:plateCounter]; } else{ NSLog(@"Number of 5s: 0"); [self setFives: 0]; } // Do 2.5s if(workingWeight &gt;= 5){ int plateCounter = 0; while(workingWeight &gt;= 5){ workingWeight = workingWeight - 5; plateCounter = plateCounter + 2; } NSLog(@"Number of 2.5s: %d", plateCounter); [self setTwoPointFives:plateCounter]; } else{ NSLog(@"Number of 2.5s: 0"); [self setTwoPointFives: 0]; } if(workingWeight &lt; 5 &amp;&amp; workingWeight != 0){ // Print something about not being exact? NSLog(@"Remaining Working Weight: %d", workingWeight); } } } else{ [self setFortyFives: 0]; [self setThirtyFives: 0]; [self setTwentyFives: 0]; [self setTens: 0]; [self setFives: 0]; [self setTwoPointFives: 0]; } } @end </code></pre> <p><strong>ViewController.m</strong></p> <pre><code>#import "ViewController.h" #import "Weights.h" #import "Weights.m" @interface ViewController () // Objects represent the text fields @property (strong, nonatomic) IBOutlet UITextField *weightField; @property (strong, nonatomic) IBOutlet UITextField *repsField; // Objectsrepresent the percentage buttons below the fields @property (strong, nonatomic) IBOutlet id nintyFiveResult; @property (strong, nonatomic) IBOutlet id nintyResult; @property (strong, nonatomic) IBOutlet id eightyFiveResult; @property (strong, nonatomic) IBOutlet id eightyResult; @property (strong, nonatomic) IBOutlet id seventyFiveResult; @property (strong, nonatomic) IBOutlet id seventyResult; @property (strong, nonatomic) IBOutlet id sixtyFiveResult; @property (strong, nonatomic) IBOutlet id sixtyResult; // Weight object used to perform the on bar calculation @property (strong, nonatomic) Weights *weightObj; // Labels represent the values on the second view @property (strong, nonatomic) IBOutlet UILabel *resultTitle; @property (strong, nonatomic) IBOutlet UILabel *fortyFivePlateLabel; @property (strong, nonatomic) IBOutlet UILabel *thirtyFivePlateLabel; @property (strong, nonatomic) IBOutlet UILabel *twentyFivePlateLabel; @property (strong, nonatomic) IBOutlet UILabel *tenPlateLabel; @property (strong, nonatomic) IBOutlet UILabel *fivePlateLabel; @property (strong, nonatomic) IBOutlet UILabel *twoFivePlateLabel; @end @implementation ViewController - (void)viewDidLoad{ [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. self.weightField.delegate = self; self.repsField.delegate = self; self.weightObj = [Weights getInstance]; } - (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated. } - (BOOL)textFieldShouldReturn:(UITextField *)textField { [textField resignFirstResponder]; return NO; } /* weightModified: This method is called when the weight field is modified. If the reps or weight value entered is equal to zero all of the percentage results will be changed to zero. If valid values are passed in both fields the percentages of weight will be calculated. */ - (IBAction)weightModified:(UITextField *)sender { NSLog(@"Weight Input Value: %@", sender.text); NSLog(@"Reps Input Value: %@", self.repsField.text); if([sender.text isEqualToString:@""] == false &amp;&amp; [self.repsField.text isEqualToString:@""] == false){ NSLog(@"Weight Modified in if statement."); // Gather reps and weight value int reps = 0; int weight = 0; weight = [sender.text intValue]; reps = [self.repsField.text intValue]; NSLog(@"Weight: %d", weight); NSLog(@"Reps: %d", reps); int nintyFiveInt = [self oneRepMax :0.95 :reps :weight]; int nintyInt = [self oneRepMax :0.9 :reps :weight]; int eightyFiveInt = [self oneRepMax :0.85 :reps :weight]; int eightyInt = [self oneRepMax :0.8 :reps :weight]; int seventyFiveInt = [self oneRepMax :0.75 :reps :weight]; int seventyInt = [self oneRepMax :0.7 :reps :weight]; int sixtyFiveInt = [self oneRepMax :0.65 :reps :weight]; int sixtyInt = [self oneRepMax :0.6 :reps :weight]; NSString *nintyFiveWeight = [NSString stringWithFormat:@"95%%: %d lbs", nintyFiveInt]; NSString *nintyWeight = [NSString stringWithFormat:@"95%%: %d lbs", nintyInt]; NSString *eightyFiveWeight = [NSString stringWithFormat:@"95%%: %d lbs", eightyFiveInt]; NSString *eightyWeight = [NSString stringWithFormat:@"95%%: %d lbs", eightyInt]; NSString *seventyFiveWeight = [NSString stringWithFormat:@"95%%: %d lbs", seventyFiveInt]; NSString *seventyWeight = [NSString stringWithFormat:@"95%%: %d lbs", seventyInt]; NSString *sixtyFiveWeight = [NSString stringWithFormat:@"95%%: %d lbs", sixtyFiveInt]; NSString *sixtyWeight = [NSString stringWithFormat:@"95%%: %d lbs", sixtyInt]; [self.nintyFiveResult setTitle:nintyFiveWeight forState:UIControlStateNormal]; [self.nintyResult setTitle:nintyWeight forState:UIControlStateNormal]; [self.eightyFiveResult setTitle:eightyFiveWeight forState:UIControlStateNormal]; [self.eightyResult setTitle:eightyWeight forState:UIControlStateNormal]; [self.seventyFiveResult setTitle:seventyFiveWeight forState:UIControlStateNormal]; [self.seventyResult setTitle:seventyWeight forState:UIControlStateNormal]; [self.sixtyFiveResult setTitle:sixtyFiveWeight forState:UIControlStateNormal]; [self.sixtyResult setTitle:sixtyWeight forState:UIControlStateNormal]; } else{ [self.nintyFiveResult setTitle:@"95%%: 0 lbs" forState:UIControlStateNormal]; [self.nintyResult setTitle:@"90%%: 0 lbs" forState:UIControlStateNormal]; [self.eightyFiveResult setTitle:@"85%%: 0 lbs" forState:UIControlStateNormal]; [self.eightyResult setTitle:@"80%%: 0 lbs" forState:UIControlStateNormal]; [self.seventyFiveResult setTitle:@"75%%: 0 lbs" forState:UIControlStateNormal]; [self.seventyResult setTitle:@"70%%: 0 lbs" forState:UIControlStateNormal]; [self.sixtyFiveResult setTitle:@"65%%: 0 lbs" forState:UIControlStateNormal]; [self.sixtyResult setTitle:@"60%%: 0 lbs" forState:UIControlStateNormal]; } } /* repsModified: This method is called when the weight field is modified. If the reps or weight value entered is equal to zero all of the percentage results will be changed to zero. If valid values are passed in both fields the percentages of weight will be calculated. */ - (IBAction)repsModified:(UITextField *)sender { if([sender.text isEqualToString:@""] == false &amp;&amp; [self.repsField.text isEqualToString:@""] == false){ NSLog(@"Reps Modified in if statement."); // Gather reps and weight value int reps = 0; int weight = 0; weight = [self.weightField.text intValue]; reps = [sender.text intValue]; NSLog(@"Weight: %d", weight); NSLog(@"Reps: %d", reps); int nintyFiveInt = [self oneRepMax :0.95 :reps :weight]; int nintyInt = [self oneRepMax :0.9 :reps :weight]; int eightyFiveInt = [self oneRepMax :0.85 :reps :weight]; int eightyInt = [self oneRepMax :0.8 :reps :weight]; int seventyFiveInt = [self oneRepMax :0.75 :reps :weight]; int seventyInt = [self oneRepMax :0.7 :reps :weight]; int sixtyFiveInt = [self oneRepMax :0.65 :reps :weight]; int sixtyInt = [self oneRepMax :0.6 :reps :weight]; NSString *nintyFiveWeight = [NSString stringWithFormat:@"95%%: %d lbs", nintyFiveInt]; NSString *nintyWeight = [NSString stringWithFormat:@"95%%: %d lbs", nintyInt]; NSString *eightyFiveWeight = [NSString stringWithFormat:@"95%%: %d lbs", eightyFiveInt]; NSString *eightyWeight = [NSString stringWithFormat:@"95%%: %d lbs", eightyInt]; NSString *seventyFiveWeight = [NSString stringWithFormat:@"95%%: %d lbs", seventyFiveInt]; NSString *seventyWeight = [NSString stringWithFormat:@"95%%: %d lbs", seventyInt]; NSString *sixtyFiveWeight = [NSString stringWithFormat:@"95%%: %d lbs", sixtyFiveInt]; NSString *sixtyWeight = [NSString stringWithFormat:@"95%%: %d lbs", sixtyInt]; [self.nintyFiveResult setTitle:nintyFiveWeight forState:UIControlStateNormal]; [self.nintyResult setTitle:nintyWeight forState:UIControlStateNormal]; [self.eightyFiveResult setTitle:eightyFiveWeight forState:UIControlStateNormal]; [self.eightyResult setTitle:eightyWeight forState:UIControlStateNormal]; [self.seventyFiveResult setTitle:seventyFiveWeight forState:UIControlStateNormal]; [self.seventyResult setTitle:seventyWeight forState:UIControlStateNormal]; [self.sixtyFiveResult setTitle:sixtyFiveWeight forState:UIControlStateNormal]; [self.sixtyResult setTitle:sixtyWeight forState:UIControlStateNormal]; } else{ [self.nintyFiveResult setTitle:@"95%%: 0 lbs" forState:UIControlStateNormal]; [self.nintyResult setTitle:@"90%%: 0 lbs" forState:UIControlStateNormal]; [self.eightyFiveResult setTitle:@"85%%: 0 lbs" forState:UIControlStateNormal]; [self.eightyResult setTitle:@"80%%: 0 lbs" forState:UIControlStateNormal]; [self.seventyFiveResult setTitle:@"75%%: 0lbs" forState:UIControlStateNormal]; [self.seventyResult setTitle:@"70%%: 0 lbs" forState:UIControlStateNormal]; [self.sixtyFiveResult setTitle:@"65%%: 0 lbs" forState:UIControlStateNormal]; [self.sixtyResult setTitle:@"60%%: 0 lbs" forState:UIControlStateNormal]; } } /* oneRepMax: This method is used to compute the one rep according to the values passed percent: represents the percentages displayed on the screen numReps: represents the number of reps in the reps field weightToLift: represents the number in the wieght field The method returns a float of the weight to be displayed on screen */ - (float)oneRepMax:(float) percent :(int) numReps :(int) weightToLift{ float r = (float) numReps; float w = (float) weightToLift; float div = r/ 30; return percent*w*div*10; } - (void) printResults:(int) percent :(int) weightOnBar :(Weights*) weightObject{ [self.resultTitle setText:[NSString stringWithFormat:@"%d%%: %d", percent, weightOnBar]]; } // Percentage Buttons - (IBAction)clickNintyFive:(id)sender { int weight = [self.weightField.text intValue]; int reps = [self.repsField.text intValue]; int nintyFiveInt = [self oneRepMax :0.95 :reps :weight]; [self printResults: 95: nintyFiveInt: _weightObj]; } - (IBAction)clickNinty:(id)sender { int weight = [self.weightField.text intValue]; int reps = [self.repsField.text intValue]; int nintyFiveInt = [self oneRepMax :0.9 :reps :weight]; [self printResults: 90: nintyFiveInt: _weightObj]; } - (IBAction)clickEightyFive:(id)sender { int weight = [self.weightField.text intValue]; int reps = [self.repsField.text intValue]; int nintyFiveInt = [self oneRepMax :0.85 :reps :weight]; [self printResults: 85: nintyFiveInt: _weightObj]; } - (IBAction)clickEighty:(id)sender { int weight = [self.weightField.text intValue]; int reps = [self.repsField.text intValue]; int nintyFiveInt = [self oneRepMax :0.8 :reps :weight]; [self printResults: 80: nintyFiveInt: _weightObj]; } - (IBAction)clickSeventyFive:(id)sender { int weight = [self.weightField.text intValue]; int reps = [self.repsField.text intValue]; int nintyFiveInt = [self oneRepMax :0.75 :reps :weight]; [self printResults: 75: nintyFiveInt: _weightObj]; } - (IBAction)clickSeventy:(id)sender { int weight = [self.weightField.text intValue]; int reps = [self.repsField.text intValue]; int nintyFiveInt = [self oneRepMax :0.7 :reps :weight]; [self printResults: 70: nintyFiveInt: _weightObj]; } - (IBAction)clickSixtyFive:(id)sender { int weight = [self.weightField.text intValue]; int reps = [self.repsField.text intValue]; int nintyFiveInt = [self oneRepMax :0.65 :reps :weight]; [self printResults: 65: nintyFiveInt: _weightObj]; } - (IBAction)clickSixty:(id)sender { int weight = [self.weightField.text intValue]; int reps = [self.repsField.text intValue]; int nintyFiveInt = [self oneRepMax :0.6 :reps :weight]; [self printResults: 60: nintyFiveInt: _weightObj]; } @end </code></pre>