Classes/MetricPickerController.m

/*
 Copyright (C) 2017 Apple Inc. All Rights Reserved.
 See LICENSE.txt for this sample’s licensing information
 
 Abstract:
 Controller to managed a picker view displaying metric weights.
 */
 
#import "MetricPickerController.h"
 
@interface MetricPickerController () <UIPickerViewDataSource, UIPickerViewDelegate>
 
@property (nonatomic, strong) IBOutlet UIPickerView *pickerView;
@property (nonatomic, strong) IBOutlet UILabel *label;
 
- (UIView *)viewForComponent:(NSInteger)component;
 
@end
 
 
#pragma mark -
 
@implementation MetricPickerController
 
// Identifiers and widths for the various components.
#define KG_COMPONENT        0
#define KG_COMPONENT_WIDTH  88
#define KG0_LABEL_WIDTH     46
 
#define G0_COMPONENT        3
#define G0_COMPONENT_WIDTH  74
#define G0_LABEL_WIDTH      44
 
#define G_COMPONENT_WIDTH   50
 
// Identifies for component views.
#define VIEW_TAG            41
#define SUB_LABEL_TAG       42
#define LABEL_TAG           43
 
 
- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView {
    
    return 4;
}
 
- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component {
    
    // Number of rows depends on the currently-selected unit and the component.
    if (component == KG_COMPONENT) {
        return 20;
    }
    return 10;
}
 
- (UIView *)labelCellWidth:(CGFloat)width rightOffset:(CGFloat)offset {
    
    // Create a new view that contains a label offset from the right.
    CGRect frame = CGRectMake(0.0, 0.0, width, 32.0);
    UIView *view = [[UIView alloc] initWithFrame:frame];
    view.tag = VIEW_TAG;
    
    frame.size.width = width - offset;
    UILabel *subLabel = [[UILabel alloc] initWithFrame:frame];
    subLabel.textAlignment = NSTextAlignmentRight;
    subLabel.backgroundColor = [UIColor clearColor];
    subLabel.font = [UIFont systemFontOfSize:24.0];
    subLabel.userInteractionEnabled = NO;
    
    subLabel.tag = SUB_LABEL_TAG;
    
    [view addSubview:subLabel];
    return view;
}
 
- (UIView *)viewForComponent:(NSInteger)component {
    
    /*
     Return a view appropriate for the specified picker view and component.
     If it's the picker view, or if it's the kg or g component of the metric view, create a UIView that contains a label.  The label can then be offset in the containing view so that its text does not overlap the unit symbol.
     For the remaining components, simple create a label to contain the text.
     Give all the views tags so they can be idntified easily.
     */
    
    if (component == KG_COMPONENT) {        
        return [self labelCellWidth:KG_COMPONENT_WIDTH rightOffset:KG0_LABEL_WIDTH];
    }
    
    if (component == G0_COMPONENT) {
        return [self labelCellWidth:G0_COMPONENT_WIDTH rightOffset:G0_LABEL_WIDTH];
    }
    
    CGRect frame = CGRectMake(0.0, 0.0, 36.0, 32.0);
    UILabel *aLabel = [[UILabel alloc] initWithFrame:frame];
    aLabel.textAlignment = NSTextAlignmentCenter;
    aLabel.backgroundColor = [UIColor clearColor];
    aLabel.font = [UIFont systemFontOfSize:24.0];
    aLabel.userInteractionEnabled = NO;
    aLabel.tag = LABEL_TAG;
    return aLabel;
}
 
- (UIView *)pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger)row forComponent:(NSInteger)component reusingView:(UIView *)view {
    
    UIView *returnView = nil;
    
    // Reuse the label if possible, otherwise create and configure a new one.
    if ((view.tag == VIEW_TAG) || (view.tag == LABEL_TAG)) {
        returnView = view;
    }
    else {
        returnView = [self viewForComponent:component];
    }
    
    // The text shown in the component is just the number of the component.
    NSString *text = [NSString stringWithFormat:@"%ld", (long)row];
    
    // Where to set the text in depends on what sort of view it is.
    UILabel *theLabel = nil;
    if (returnView.tag == VIEW_TAG) {
        theLabel = (UILabel *)[returnView viewWithTag:SUB_LABEL_TAG];
    }
    else {
        theLabel = (UILabel *)returnView;
    }
    
    theLabel.text = text;
    return returnView;
}
 
- (CGFloat)pickerView:(UIPickerView *)pickerView widthForComponent:(NSInteger)component {
    
    // The width of the component depends on the currently-selected unit and the component.
    
    if (component == KG_COMPONENT) {
        return KG_COMPONENT_WIDTH;
    }
    if (component == G0_COMPONENT) {
        return G0_COMPONENT_WIDTH;
    }
    return G_COMPONENT_WIDTH;   
}
 
- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component {
    
    // If the user chooses a new row, update the label accordingly.
    [self updateLabel];
}
 
- (void)updateLabel {
    
    /*
     If the user has entered metric units, find the number of grams and convert that to pounds and ounces.
     Don't display 0 lbs; round 15.95 ounces up to 1 lb, and use NSDecimalNumberHandler to round ounces for a more attractive display.
     */
    
    static NSDecimalNumberHandler* roundingBehavior = nil;
    
    if (roundingBehavior == nil) {
        roundingBehavior = 
        [[NSDecimalNumberHandler alloc] initWithRoundingMode:NSRoundPlain
                                                       scale:1
                                            raiseOnExactness:NO
                                             raiseOnOverflow:NO
                                            raiseOnUnderflow:NO
                                         raiseOnDivideByZero:NO];
    }       
    
    NSInteger grams = 0;
    grams += [self.pickerView selectedRowInComponent:3];
    grams += [self.pickerView selectedRowInComponent:2] * 10;
    grams += [self.pickerView selectedRowInComponent:1] * 100;
    grams += [self.pickerView selectedRowInComponent:0] * 1000;
    
    NSDecimalNumber *ouncesDecimal;
    NSDecimalNumber *roundedOunces;
    
    float ounces = grams / 28.349;
    
    if (ounces >= 15.95) {
        NSInteger lbs = ounces / 16;
        ounces -= lbs * 16;
        if (ounces >= 15.95) {
            ounces = 0;
            lbs += 1;
        }
        ouncesDecimal = [[NSDecimalNumber alloc] initWithFloat:ounces];
        roundedOunces = [ouncesDecimal decimalNumberByRoundingAccordingToBehavior:roundingBehavior];
        self.label.text = [NSString stringWithFormat:@"%ld lbs  %@ oz", (long)lbs, roundedOunces];
    }
    else {
        ouncesDecimal = [[NSDecimalNumber alloc] initWithFloat:ounces];
        roundedOunces = [ouncesDecimal decimalNumberByRoundingAccordingToBehavior:roundingBehavior];
        self.label.text = [NSString stringWithFormat:@"%@ oz", roundedOunces];
    }
}
 
@end


Copyright © 2017 Apple Inc. All Rights Reserved. Terms of Use | Privacy Policy | Updated: 2017-07-20