Uncertain about public or private variable declaration and self delegate? - ios

Question

I'm very new to Objective-C and iOS development in general. This week I managed to get a small app running correctly in the simulator after large efforts.
I've pickup basics of the programming language by reading in "iOS 7 Programming Fundamentals" by Matt Neuburg, instructions from tutorials online and from suggestions on this website.
I've written code that works (apparently), but I do not fully understand why I needed to make several adjustments in my code to make it work.
The app is a basic one which solves a "wind triangle" for your information. All it needs to do, is putting some user defined variables in the correct formula, and display the outcome.
I've copied the .h and .m file. Simply said: the .h declares 7 variables; 5 user inputs in a textfield; 2 labels to display 2 calculated outcomes; one button which initiates the action to calculate.
With following code, I do not understand:
why I was forced to state my variables preceded by a underscore to use in the implementation
why I was forced to declare .delegate to 'self' for the variables after loading the view
Any suggestions to make this 'app' more logical and easier to understand (by myself) ?
//
// ViewController.h
// WindTriangle
//
#import <UIKit/UIKit.h>
#define M_PI 3.14159265358979323846264338327950288 /* pi */
float windDegreesFloat;
float windSpeedFloat;
float courseDesiredFloat;
float trueAirSpeedFloat;
float magneticVariationFloat;
float headingCalculatedFloat;
float groundSpeedCalculatedFloat;
#interface ViewController : UIViewController<UITextFieldDelegate>
#property (weak, nonatomic) IBOutlet UITextView *instructionsText;
#property (weak, nonatomic) IBOutlet UITextField *windDegrees;
#property (weak, nonatomic) IBOutlet UITextField *windSpeed;
#property (weak, nonatomic) IBOutlet UITextField *courseDesired;
#property (weak, nonatomic) IBOutlet UITextField *trueAirSpeed;
#property (weak, nonatomic) IBOutlet UITextField *magneticVariation;
#property (weak, nonatomic) IBOutlet UILabel *headingCalculated;
#property (weak, nonatomic) IBOutlet UILabel *groundSpeedCalculated;
- (IBAction)calculatePressed:(id)sender;
#end
And
//
// ViewController.m
// WindTriangle
//
#import "ViewController.h"
#interface ViewController ()
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
self.windDegrees.delegate = self;
self.windSpeed.delegate = self;
self.courseDesired.delegate = self;
self.trueAirSpeed.delegate = self;
self.magneticVariation.delegate = self;
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (IBAction)calculatePressed:(id)sender {
windDegreesFloat = [_windDegrees.text floatValue];
windSpeedFloat = [_windSpeed.text floatValue];
courseDesiredFloat = [_courseDesired.text floatValue];
trueAirSpeedFloat = [_trueAirSpeed.text floatValue];
magneticVariationFloat = [_magneticVariation.text floatValue];
headingCalculatedFloat = ( courseDesiredFloat - magneticVariationFloat ) + ( 180 / M_PI ) * asin(( windSpeedFloat / trueAirSpeedFloat) * sin(( M_PI * ( windDegreesFloat - ( courseDesiredFloat - magneticVariationFloat))) / 180));
NSString * headingCalculatedString = [NSString stringWithFormat:#"%.1f", headingCalculatedFloat];
_headingCalculated.text = headingCalculatedString;
groundSpeedCalculatedFloat = sqrt(pow( trueAirSpeedFloat , 2) + pow(windSpeedFloat , 2) - (2 * trueAirSpeedFloat *windSpeedFloat * cos((M_PI * ( courseDesiredFloat - windDegreesFloat + ((180 / M_PI) * asin(( windSpeedFloat / trueAirSpeedFloat ) * sin((M_PI * ( windDegreesFloat - courseDesiredFloat )) / 180))))) / 180)));
NSString * groundSpeedCalculatedString = [NSString stringWithFormat:#"%.1f", groundSpeedCalculatedFloat];
_groundSpeedCalculated.text = groundSpeedCalculatedString;
}
- (BOOL)textFieldShouldReturn:(UITextField *)textField
{
return [textField resignFirstResponder];
}
#end
I'm brandnew to StackOverflow as well. Your comments will be much appreciated.

Answer 1

Hey so for your first question, the underscore indicates instance variables. Sometime back, you couldn't do this in objective c. If you declared a property, you had to call it through self.property after synthesizing it. So the underscore is just calling an instance.
As for the second question when you set the delegate in this case you're actually setting the delegate of the IBOutlet for the UITextField as the viewcontroller you're typing the code in. A delegate is responsible for the interaction between the controller and the view. This allows the view controller to manage certain methods of the UITextFieldDelegate

Answer 2

When you declare #property, for example:
#property (weak, nonatomic) UITextField *property;
Compiler create public variable, which you can access by self.property and private variable, which you access with underscore _property.
In your implementation you read private variable by adding underscore.
The delegate is a way for object to inform another object about something. In your example:
self.windDegrees.delegate = self;
self.windDegrees is a text field and this instruction means that this text field (windDegrees) will inform current class (ViewController) that something happened, for example method:
- (BOOL)textFieldShouldReturn:(UITextField *)textField
{
return [textField resignFirstResponder];
}
will be called every time your text fields should return.

Answer 3

You have several things wrong here. Your .h file should be:
//
// ViewController.h
// WindTriangle
//
#import <UIKit/UIKit.h>
#interface ViewController : UIViewController
#property (weak, nonatomic) IBOutlet UITextView *instructionsText;
#property (weak, nonatomic) IBOutlet UITextField *windDegrees;
#property (weak, nonatomic) IBOutlet UITextField *windSpeed;
#property (weak, nonatomic) IBOutlet UITextField *courseDesired;
#property (weak, nonatomic) IBOutlet UITextField *trueAirSpeed;
#property (weak, nonatomic) IBOutlet UITextField *magneticVariation;
#property (weak, nonatomic) IBOutlet UILabel *headingCalculated;
#property (weak, nonatomic) IBOutlet UILabel *groundSpeedCalculated;
- (IBAction)calculatePressed:(id)sender;
#end
You do not want to declare all of those unnecessary global variables. You do not need to redefine the standard M_PI macro. And you do not need to tell the world that your class conforms to the UITextField protocol.
In your .m file you should replace this:
#interface ViewController ()
#end
with:
#interface ViewController () <UITextViewDelegate, UITextFieldDelegate>
#end
Also, everywhere you reference one of the generated instance variables for one of your properties, you should change the reference to use the property instead. Example:
Change:
windDegreesFloat = [_windDegrees.text floatValue];
to:
windDegreesFloat = [self.windDegrees.text floatValue];
Do this everywhere you use the underscored variable instead of the property.
The use of self.windDegrees.delegate = self;, for example, is to tell the text field that your view controller (self) will be handling events from the text field.

Answer 4

Thanks for all the feedback. I changed the code with your feedback to following code.
As it worked before, it still does, but with correct(er) coding.
I'm starting to understand why I had to remove the global variables in .h, where to put correct protocol declarations, and also where the _ really stands for. Additional comments or thoughts are welcome. thx all !
//
// ViewController.h
// WindTriangle
//
#import <UIKit/UIKit.h>
#interface ViewController : UIViewController<UITextFieldDelegate>
#property (weak, nonatomic) IBOutlet UITextView *instructionsText;
#property (weak, nonatomic) IBOutlet UITextField *windDegrees;
#property (weak, nonatomic) IBOutlet UITextField *windSpeed;
#property (weak, nonatomic) IBOutlet UITextField *courseDesired;
#property (weak, nonatomic) IBOutlet UITextField *trueAirSpeed;
#property (weak, nonatomic) IBOutlet UITextField *magneticVariation;
#property (weak, nonatomic) IBOutlet UILabel *headingCalculated;
#property (weak, nonatomic) IBOutlet UILabel *groundSpeedCalculated;
- (IBAction)calculatePressed:(id)sender;
#end
And
//
// ViewController.m
// WindTriangle
//
#import "ViewController.h"
#interface ViewController () <UITextViewDelegate, UITextFieldDelegate>
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
self.windDegrees.delegate = self;
self.windSpeed.delegate = self;
self.courseDesired.delegate = self;
self.trueAirSpeed.delegate = self;
self.magneticVariation.delegate = self;
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (IBAction)calculatePressed:(id)sender {
float windDegreesFloat = [self.windDegrees.text floatValue];
float windSpeedFloat = [self.windSpeed.text floatValue];
float courseDesiredFloat = [self.courseDesired.text floatValue];
float trueAirSpeedFloat = [self.trueAirSpeed.text floatValue];
float magneticVariationFloat = [self.magneticVariation.text floatValue];
float headingCalculatedFloat = ( courseDesiredFloat - magneticVariationFloat ) + ( 180 / M_PI ) * asin(( windSpeedFloat / trueAirSpeedFloat) * sin(( M_PI * ( windDegreesFloat - ( courseDesiredFloat - magneticVariationFloat))) / 180));
NSString * headingCalculatedString = [NSString stringWithFormat:#"%.1f", headingCalculatedFloat];
_headingCalculated.text = headingCalculatedString;
float groundSpeedCalculatedFloat = sqrt(pow( trueAirSpeedFloat , 2) + pow(windSpeedFloat , 2) - (2 * trueAirSpeedFloat *windSpeedFloat * cos((M_PI * ( courseDesiredFloat - windDegreesFloat + ((180 / M_PI) * asin(( windSpeedFloat / trueAirSpeedFloat ) * sin((M_PI * ( windDegreesFloat - courseDesiredFloat )) / 180))))) / 180)));
NSString * groundSpeedCalculatedString = [NSString stringWithFormat:#"%.1f", groundSpeedCalculatedFloat];
_groundSpeedCalculated.text = groundSpeedCalculatedString;
}
- (BOOL)textFieldShouldReturn:(UITextField *)textField
{
return [textField resignFirstResponder];
}
#end