UIScrollViewAutolayout.m

//
//  ViewController.m
//  UIScrollViewAutoLayout
//
//  Created by Bart Vandendriessche on 11/10/14.
//  Copyright (c) 2014 Bart Vandendriessche. Copy freely and of your own will.
//

#import "ViewController.h"

@interface ViewController ()

@property (nonatomic, strong) UIScrollView *scrollView;
@property (nonatomic, strong) UILabel *label1;
@property (nonatomic, strong) UILabel *label2;
@property (nonatomic, strong) UILabel *label3;
@property (nonatomic, strong) UILabel *label4;

@property (nonatomic, copy) NSString *shortText;
@property (nonatomic, copy) NSString *longText;

@end


CGFloat const StandardInset = 20;


@implementation ViewController

- (instancetype)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        self.shortText = @"label 2";
        self.longText = @"Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nullam eros dui, lacinia eu mauris ac, bibendum imperdiet nulla. Nam sagittis tempus pellentesque. Ut at eleifend enim. Nam magna lorem, lobortis at ante non, facilisis fringilla elit. Nulla facilisi. Quisque efficitur felis at dui rutrum tempus. Cras sem urna, venenatis quis erat vitae, euismod mollis diam. Ut et rutrum nunc, eu consequat est. Proin imperdiet vestibulum neque, vitae suscipit diam porta eu. Nunc sagittis venenatis nibh, tristique venenatis nunc convallis eget. Aliquam in massa eget mauris aliquet mattis. In ac pulvinar ante. Curabitur ac imperdiet neque. Sed facilisis quis mi non porttitor. Donec commodo et est at accumsan. Fusce interdum, lacus nec lacinia venenatis, ante ante pretium nulla, vitae dapibus lorem nisi eu risus./n/nProin blandit lacus sed laoreet vulputate. Suspendisse libero orci, fermentum eu aliquet ac, aliquam vitae tellus. Ut vitae porttitor magna. Nullam id quam non mauris volutpat interdum sed eu ante. Mauris hendrerit fermentum nisl eu auctor. Phasellus luctus aliquam dolor et placerat. Maecenas scelerisque, dolor nec iaculis iaculis, augue nunc consequat velit, eu ullamcorper purus libero eget enim. Sed vel ipsum id neque fermentum lobortis id sit amet dui. Nulla lacinia enim non mattis dictum. Nullam dapibus lacinia tristique. Pellentesque id posuere mi, sed efficitur ex.";
    }
    return self;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
    
    [self.scrollView addSubview:self.label1];
    [self.scrollView addSubview:self.label2];
    [self.scrollView addSubview:self.label3];
    [self.scrollView addSubview:self.label4];
    
    [self.view addSubview:self.scrollView];
    
    [self setupConstraints];
    
    self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"Toggle" style:UIBarButtonItemStylePlain target:self action:@selector(toggle:)];
}

- (void)setupConstraints {
    
    // pin the scrollview to its superview edges (make it fill the screen)
    for (id attribute in @[@(NSLayoutAttributeTop), @(NSLayoutAttributeLeft), @(NSLayoutAttributeBottom), @(NSLayoutAttributeRight)]) {
        [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.scrollView
                                                              attribute:[attribute integerValue]
                                                              relatedBy:NSLayoutRelationEqual
                                                                 toItem:self.view
                                                              attribute:[attribute integerValue]
                                                             multiplier:1
                                                               constant:0]];
    }

    
    
    // pin label1 to the top side of the scrollview
    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.label1
                                                          attribute:NSLayoutAttributeTop
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:self.scrollView
                                                          attribute:NSLayoutAttributeTop
                                                         multiplier:1
                                                           constant:StandardInset]];
    
    UIView *topAnchor;
    for (UILabel *label in @[self.label1, self.label2, self.label3, self.label4]) {
        // pin all labels to the left side of the scrollview
        [self.view addConstraint:[NSLayoutConstraint constraintWithItem:label
                                                              attribute:NSLayoutAttributeLeft
                                                              relatedBy:NSLayoutRelationEqual
                                                                 toItem:self.scrollView
                                                              attribute:NSLayoutAttributeLeft
                                                             multiplier:1
                                                               constant:StandardInset]];
        
        // pin all labels to the right side of the scrollview
        [self.view addConstraint:[NSLayoutConstraint constraintWithItem:label
                                                              attribute:NSLayoutAttributeRight
                                                              relatedBy:NSLayoutRelationEqual
                                                                 toItem:self.scrollView
                                                              attribute:NSLayoutAttributeRight
                                                             multiplier:1
                                                               constant:StandardInset]];
        
        // assign a width constraint to the labels. This constraint can NOT be relative to the scrollView
        [self.view addConstraint:[NSLayoutConstraint constraintWithItem:label
                                                              attribute:NSLayoutAttributeWidth
                                                              relatedBy:NSLayoutRelationEqual
                                                                 toItem:self.view
                                                              attribute:NSLayoutAttributeWidth
                                                             multiplier:1
                                                               constant:-( 2 * StandardInset)]];
        
        // pin all labels to the bottom of the previous label
        if (topAnchor) {
            [self.view addConstraint:[NSLayoutConstraint constraintWithItem:label
                                                                  attribute:NSLayoutAttributeTop
                                                                  relatedBy:NSLayoutRelationEqual
                                                                     toItem:topAnchor
                                                                  attribute:NSLayoutAttributeBottom
                                                                 multiplier:1
                                                                   constant:StandardInset]];
        }
        
        topAnchor = label;
    }
    
    // pin label4 to the bottom of the scrollview
    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.label4
                                                          attribute:NSLayoutAttributeBottom
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:self.scrollView
                                                          attribute:NSLayoutAttributeBottom
                                                         multiplier:1
                                                           constant:StandardInset]];
    
    
}

#pragma mark - Actions

- (void)toggle:(id)sender {
    if ([self.label2.text isEqualToString:self.shortText]) {
        self.label2.text = self.longText;
    } else {
        self.label2.text = self.shortText;
    }
    
    [self.label2 invalidateIntrinsicContentSize];
}

#pragma mark - Lazy subviews

- (UIScrollView *)scrollView {
    if (_scrollView) {
        return _scrollView;
    }
    
    _scrollView = [[UIScrollView alloc] init];
    _scrollView.translatesAutoresizingMaskIntoConstraints = NO;
    _scrollView.backgroundColor = [UIColor yellowColor];
    
    return _scrollView;
}

- (UILabel *)label1 {
    if (_label1) {
        return _label1;
    }
    
    _label1 = [[UILabel alloc] init];
    _label1.translatesAutoresizingMaskIntoConstraints = NO;
    _label1.text = @"Label 1";
    _label1.backgroundColor = [UIColor redColor];
    
    return _label1;
}

- (UILabel *)label2 {
    if (_label2) {
        return _label2;
    }
    
    _label2 = [[UILabel alloc] init];
    _label2.translatesAutoresizingMaskIntoConstraints = NO;
    _label2.text = self.longText;
    _label2.backgroundColor = [UIColor greenColor];
    
    _label2.numberOfLines = 0;
    
    return _label2;
}

- (UILabel *)label3 {
    if (_label3) {
        return _label3;
    }
    
    _label3 = [[UILabel alloc] init];
    _label3.translatesAutoresizingMaskIntoConstraints = NO;
    _label3.text = @"Label 3";
    _label3.backgroundColor = [UIColor purpleColor];
    
    return _label3;
}

- (UILabel *)label4 {
    if (_label4) {
        return _label4;
    }
    
    _label4 = [[UILabel alloc] init];
    _label4.translatesAutoresizingMaskIntoConstraints = NO;
    _label4.text = @"Label 4";
    _label4.backgroundColor = [UIColor blueColor];
    
    return _label4;
}

@end