自动布局（代码）

- (void)viewDidLoad {

[super viewDidLoad];

// Do any additional setup after loading the view, typically from a nib.

UIImageView *logoImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"apple.jpg"]];

logoImageView.translatesAutoresizingMaskIntoConstraints = NO;

logoImageView.contentMode = UIViewContentModeScaleAspectFit;

[self.view addSubview:logoImageView];

// 水平方向

NSArray* hConstraintArray = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-0-[logoImageView]-0-|" options:0 metrics:nil views:@{@"logoImageView": logoImageView}];

[NSLayoutConstraint activateConstraints:hConstraintArray];

// 垂直

NSArray *vConstraintArray = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-0-[logoImageView]" options:0 metrics:nil views:@{@"logoImageView":logoImageView}];

[NSLayoutConstraint activateConstraints:vConstraintArray];

// 底部

NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:logoImageView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeHeight multiplier:0.5f constant:0.0f];

heightConstraint.active = YES;

//

// UIImageView *logoImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"apple.jpg"]];

// logoImageView.backgroundColor = [UIColor orangeColor];

// logoImageView.translatesAutoresizingMaskIntoConstraints = NO;

// logoImageView.contentMode = UIViewContentModeScaleAspectFit;

// [self.view addSubview:logoImageView];

//

// // 水平方向

// NSArray *hContraintArray = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-50-[logoImageView]-0-|" options:0 metrics:nil views:@{@"logoImageView":logoImageView}];

// [NSLayoutConstraint activateConstraints:hContraintArray];

//

// // 垂直方向

// NSArray *vContraintArray = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-0-[logoImageView]" options:0 metrics:nil views:@{@"logoImageView":logoImageView}];

// [NSLayoutConstraint activateConstraints:vContraintArray];

//

// // 底部高度

// NSLayoutConstraint *bConstraintHeight = [NSLayoutConstraint constraintWithItem:logoImageView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeHeight multiplier:0.25f constant:0];

// bConstraintHeight.active = YES;

// 添加scrollView

UIScrollView *scrollView = [[UIScrollView alloc] init];

scrollView.translatesAutoresizingMaskIntoConstraints = NO;

scrollView.backgroundColor = [UIColor greenColor];

[self.view addSubview:scrollView];

NSArray *hScrollViewConstraintArray = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[scrollView]|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(scrollView)];

[NSLayoutConstraint activateConstraints:hScrollViewConstraintArray];

NSArray *vScrollViewConstraintArray = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|[logoImageView][scrollView]|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(logoImageView,scrollView)];

[NSLayoutConstraint activateConstraints:vScrollViewConstraintArray];

// label

UILabel *nameLabel = [[UILabel alloc] init];

nameLabel.text = @"做程序，先学会思维";

nameLabel.textColor = [UIColor blackColor];

nameLabel.translatesAutoresizingMaskIntoConstraints = NO;

nameLabel.backgroundColor = [UIColor purpleColor];

[scrollView addSubview:nameLabel];

UILabel *descriptionLabel = [UILabel new];

descriptionLabel.translatesAutoresizingMaskIntoConstraints = NO;

descriptionLabel.text = @"思维思维思维四；逻辑逻辑逻辑逻辑例句逻辑逻辑逻辑哦邻居哦";

descriptionLabel.numberOfLines = 0;

descriptionLabel.backgroundColor = [UIColor orangeColor];

[scrollView addSubview:descriptionLabel];

// 水平方向上，nameLabel左侧与父视图左侧对齐，nameLabel右侧与父视图右侧对齐，nameLabel宽度与logoImageView宽度相同

NSArray *hNameLabelConstraintArray = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[nameLabel(==logoImageView)]|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(nameLabel, logoImageView)];

[NSLayoutConstraint activateConstraints:hNameLabelConstraintArray];

// 水平方向上，descriptionLabel左侧与父视图左侧对齐，descriptionLabel右侧与父视图右侧对齐，descriptionLabel宽度与logoImageView宽度相同

NSArray *hDescriptionLabelConstraintArray = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[descriptionLabel(==logoImageView)]|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(descriptionLabel, logoImageView)];

[NSLayoutConstraint activateConstraints:hDescriptionLabelConstraintArray];

// 垂直方向上，nameLabel顶部与父视图顶部对齐，nameLabel高度为20，nameLabel底部与descriptionLabel顶部对齐，descriptionLabel底部与父视图底部对齐

NSArray *vLabelConstraintArray = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|[nameLabel(20)][descriptionLabel]|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(nameLabel, descriptionLabel)];

[NSLayoutConstraint activateConstraints:vLabelConstraintArray];

}

运行截图如下：