How to execute a if loop when i press the convert button objective c, xcode - objective-c

Question

This is my .h file in xcode
//
// PickerViewController.h
// Picker
//
// Created by jitin on 9/14/14.
// Copyright (c) 2014 jitin. All rights reserved.
//
#import <UIKit/UIKit.h>
#interface PickerViewController : UIViewController <UIPickerViewDelegate, UIPickerViewDataSource> {
IBOutlet UIPickerView *picker;
}
#property (nonatomic, retain) UIPickerView *picker;
#property (weak, nonatomic) IBOutlet UITextField *txtbox1;
#property (weak, nonatomic) IBOutlet UITextField *txtbox2;
#property (weak, nonatomic) IBOutlet UITextField *txtbox3;
#property (weak, nonatomic) IBOutlet UITextField *txtbox4;
-(IBAction)convert:(id)sender;
#end
this is my .m file using xcode
//
// PickerViewController.m
// Picker
//
// Created by jitin on 9/14/14.
// Copyright (c) 2014 jitin. All rights reserved.
//
#import "PickerViewController.h"
#interface PickerViewController ()
#end
#implementation PickerViewController
#synthesize picker;
#synthesize txtbox1, txtbox2, txtbox3, txtbox4;
static NSString *pd[3] = {#"Farenheit", #"Feet", #"Grams"};
static NSString *pd2[3] = {#"Celcius", #"Inches", #"Kilograms"};
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#pragma mark UIPickerViewDelegate & UIPickerViewDataSource methods
-(NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView
{
return 1;
}
-(NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component
{
return 3;
}
-(NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component;
{
return pd[row];
}
-(void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component
{
NSLog(#"didSelectRow: %li, inComponent: %li", row, (long)component);
self.txtbox1.text = pd[row];
self.txtbox2.text = pd2[row];
}
#pragma mark Rotation
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
NSLog(#"Current Row Select Value %li", [picker selectedRowInComponent:0]);
// Return YES for supported orientations
return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}
-(BOOL)shouldAutorotate {
NSLog(#"Current Row Select Value %li", [picker selectedRowInComponent:0]);
return YES;
}
-(IBAction)convert:(id)sender
{
float inValue = [[txtbox3 text] floatValue];
float outValue = ((inValue * (9.0f/5.0f)) + 32);
[txtbox4 setText:[NSString stringWithFormat:#"%3.2f", outValue]];
}
#end
my question is about the convert method/function in my .m file.
I want to do a if loop based on what row is selected in the pickerview. for example. if row 0 is selected, the conversion would be Fahrenheit to Celsius.
if row 1 is selected the conversion would be feet to inches when i hit the convert button. I know I have to use a if loop. But i'm having trouble on what to call in that if loop in order for my statements to execute correctly. Another note. I have not implemented my feets to inches and the grams to kilograms conversion yet. I just wanna get my if loop working first.

Answer 1

Hi #user7897479 and welcome.
My recommendation would be to use a "UnitConversion" class to hold all the relevant information about the units and perform the conversions for you. This separates the responsibilities so that your ViewController only really has the responsibility of passing data between the UI Elements <-> conversion class.
One other thing that i'd like to mention before I get into my full answer:
Naming is very important! Please give meaningful names to your properties/methods/objects/classes -- This will help not only others looking at your code, but yourself going forward maintaining it
Looking at this without much idea about your interface, I have no clue what txtbox1,2,3,4 are for, or for that matter what type of strings pd, pd2 (if I was just looking at them without the literals defined).
Ok, onto some code:
UnitConversion.h:
#import <Foundation/Foundation.h>
typedef enum : NSUInteger {
UnitConversionTypeFarenheightToCelsius,
UnitConversionTypeFeetToInches,
UnitConversionTypeGramsToKilograms,
} UnitConversionType;
NS_ASSUME_NONNULL_BEGIN
#interface UnitConversion : NSObject
- (instancetype _Nullable)initWithUnitConversionType:(UnitConversionType)type;
- (NSString *)nameForConvertFromUnit;
- (NSString *)nameForConvertToUnit;
- (NSString *)runConversionOnValue:(float)value;
#end
NS_ASSUME_NONNULL_END
UnitConversion.m:
#import "UnitConversion.h"
typedef enum : NSUInteger {
ConversionUnitFarenheit,
ConversionUnitFeet,
ConversionUnitGrams,
ConversionUnitCelsius,
ConversionUnitInches,
ConversionUnitKilograms,
} ConversionUnit;
#interface UnitConversion()
#property ConversionUnit convertFromUnit;
#property ConversionUnit convertToUnit;
#property UnitConversionType conversionType;
#property float valueToConvert;
#end
#implementation UnitConversion
- (instancetype _Nullable)initWithUnitConversionType:(UnitConversionType)type {
self = [super init];
if (self) {
_conversionType = type;
switch (type) {
case UnitConversionTypeFarenheightToCelsius: {
_convertFromUnit = ConversionUnitFarenheit;
_convertToUnit = ConversionUnitCelsius;
break;
}
case UnitConversionTypeFeetToInches: {
_convertFromUnit = ConversionUnitFeet;
_convertToUnit = ConversionUnitInches;
break;
}
case UnitConversionTypeGramsToKilograms: {
_convertFromUnit = ConversionUnitGrams;
_convertToUnit = ConversionUnitKilograms;
break;
}
default:
break;
}
}
return self;
}
- (NSString *)runConversionOnValue:(float)value {
self.valueToConvert = value;
NSString *convertedValue = #"Undefined";
switch (self.conversionType) {
case UnitConversionTypeFarenheightToCelsius:
convertedValue = [self _convertFarenheightToCelsius];
break;
case UnitConversionTypeFeetToInches:
convertedValue = [self _convertFeetToInches];
break;
case UnitConversionTypeGramsToKilograms:
convertedValue = [self _convertGramsToKilograms];
break;
default:
break;
}
return convertedValue;
}
- (NSString *)_convertFarenheightToCelsius {
return [NSString stringWithFormat:#"%.2f", (self.valueToConvert - 32.0f) * (5.0f/9.0f)];
}
- (NSString *)_convertFeetToInches {
return [NSString stringWithFormat:#"%.2f", self.valueToConvert / 12.0f];
}
- (NSString *)_convertGramsToKilograms {
return [NSString stringWithFormat:#"%.2f", self.valueToConvert / 1000.0f];
}
- (NSString *)nameForConvertFromUnit {
return [self _nameForConversionUnit:self.convertFromUnit];
}
- (NSString *)nameForConvertToUnit {
return [self _nameForConversionUnit:self.convertToUnit];
}
- (NSString *)_nameForConversionUnit:(ConversionUnit)unit {
NSString *unitName = #"Default Unit";
switch (unit) {
case ConversionUnitFarenheit: {
unitName = #"Farenheit";
break;
}
case ConversionUnitFeet: {
unitName = #"Feet";
break;
}
case ConversionUnitGrams: {
unitName = #"Grams";
break;
}
case ConversionUnitCelsius: {
unitName = #"Celsius";
break;
}
case ConversionUnitInches: {
unitName = #"Inches";
break;
}
case ConversionUnitKilograms: {
unitName = #"Kilograms";
break;
}
default:
break;
}
return unitName;
}
#end
ConversionViewController.m:
#import "ConversionViewController.h"
#import "UnitConversion.h"
#interface ConversionViewController () <UIPickerViewDelegate, UIPickerViewDataSource, UITextFieldDelegate>
#property (strong, nullable) IBOutlet UIPickerView *conversionPicker;
#property (strong, nullable) NSArray <UnitConversion *> *unitConversionArray;
#property (strong, nullable) IBOutlet UILabel *convertFromLabel;
#property (strong, nullable) IBOutlet UILabel *convertToLabel;
#property (strong, nullable) IBOutlet UITextField *convertFromValue;
#property (strong, nullable) IBOutlet UITextField *convertToValue;
#end
#implementation ConversionViewController
- (void)viewDidLoad {
[super viewDidLoad];
// setup the conversion we want to do and put them into our data structure
UnitConversion *degreesConversion = [[UnitConversion alloc] initWithUnitConversionType:UnitConversionTypeFarenheightToCelsius];
UnitConversion *inchesToFeet = [[UnitConversion alloc] initWithUnitConversionType:UnitConversionTypeFeetToInches];
UnitConversion *gramsToKilo = [[UnitConversion alloc] initWithUnitConversionType:UnitConversionTypeGramsToKilograms];
self.unitConversionArray = #[degreesConversion, inchesToFeet, gramsToKilo];
}
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
// by default select the first row
[self.conversionPicker selectRow:0 inComponent:0 animated:NO];
}
- (IBAction)convert:(id)sender {
NSInteger pickerRow = [self.conversionPicker selectedRowInComponent:0];
if (pickerRow >= 0) {
// grab our associated UnitConversion based on our backing unit conversion array
// the index matches up with the index selected for the picker row
UnitConversion *conversion = [self.unitConversionArray objectAtIndex:pickerRow];
// run the conversion
NSString *convertedValue = [conversion runConversionOnValue:[self.convertFromValue.text floatValue]];
// set the converted value to our result field
self.convertToValue.text = convertedValue;
}
}
- (NSInteger)numberOfComponentsInPickerView:(nonnull UIPickerView *)pickerView {
return 1;
}
- (NSInteger)pickerView:(nonnull UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component {
return 3;
}
- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component {
// clear out our input and output fields
self.convertFromValue.text = #"";
self.convertToValue.text = #"";
// set the labels to alpha 0 because we going to fade in the change
self.convertFromLabel.alpha = 0.0f;
self.convertToLabel.alpha = 0.0f;
// determine which conversion is selected from the picker view
UnitConversion *conversion = [self.unitConversionArray objectAtIndex:row];
// set our labels to reflect that
self.convertFromLabel.text = [conversion nameForConvertFromUnit];
self.convertToLabel.text = [conversion nameForConvertToUnit];
// now animate the fade in of our label names
[UIView animateWithDuration:0.2 animations:^{
self.convertFromLabel.alpha = 1.0f;
self.convertToLabel.alpha = 1.0f;
}];
}
- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component {
// our titles should be in the form of "Feet to Inches"
UnitConversion *conversion = [self.unitConversionArray objectAtIndex:row];
return [NSString stringWithFormat:#"%# to %#", [conversion nameForConvertFromUnit], [conversion nameForConvertToUnit]];
}
#pragma mark - UITextFieldDelegate
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
// only allow numbers decimal and negative
NSCharacterSet *numbersOnly = [NSCharacterSet characterSetWithCharactersInString:#"0123456789.-"];
NSCharacterSet *characterSetFromTextField = [NSCharacterSet characterSetWithCharactersInString:textField.text];
// don't allow the text field to change if the user attempts to input something else
BOOL stringIsValid = [numbersOnly isSupersetOfSet:characterSetFromTextField];
return stringIsValid;
}
#end
Here's an example of what that Code produces after generating a simple interface:
While this does seem like overkill for the example, it makes it a lot easier to expand upon it (for example if you wanted to add additional conversion types, or re-use the conversion class somewhere else).