iOS AutoLayout 中的ContentHugging 和 ContentCompressionResistance

iOS 6 中引入了AutoLayout，像UILabel、UIButton等控件设置text和font之后可以自动计算控件大小，是因为ContentHugging 和 ContentCompressionResistance
相关函数如下

- (UILayoutPriority)contentHuggingPriorityForAxis:(UILayoutConstraintAxis)axis NS_AVAILABLE_IOS(6_0);
- (void)setContentHuggingPriority:(UILayoutPriority)priority forAxis:(UILayoutConstraintAxis)axis NS_AVAILABLE_IOS(6_0);

- (UILayoutPriority)contentCompressionResistancePriorityForAxis:(UILayoutConstraintAxis)axis NS_AVAILABLE_IOS(6_0);
- (void)setContentCompressionResistancePriority:(UILayoutPriority)priority forAxis:(UILayoutConstraintAxis)axis NS_AVAILABLE_IOS(6_0);

ContentHuggingPriority 确定view有多大优先级阻止自己变大，默认为250
ContentCompressionResistancePriority 确定view有多大优先级阻止自己变小，默认为750
示例
有三个文本，文本一、文本二、文本三，在一行，显示优先级为文本一>文本二>文本三，也就是优先显示文本一的内容，再次为文本二的内容，最后显示文本三的内容。我们可以修改ContentHuggingPriority和ContentCompressionResistancePriority来实现。
会用到第三方库Masonry，https://github.com/SnapKit/Masonry
主界面如下

1.png

只显示文本一内容时，如下

2.png

显示文本一和文本二内容时，如下

3.png

文本一和文本二以及文本三内容都显示时，如下

4.png

主代码如下

#import "ViewController.h"
#import "Masonry.h"

@interface ViewController ()

/** UI */
@property (nonatomic, strong) UILabel *labelOne;

@property (nonatomic, strong) UILabel *labelTwo;

@property (nonatomic, strong) UILabel *labelThree;

@property (nonatomic, strong) UIImageView *qrCodeImgView;

@property (nonatomic, strong) UILabel *signLabel;

@end

@implementation ViewController

#pragma mark - life cycle
- (void)viewDidLoad
{
    [super viewDidLoad];
    self.title = @"点滴86";
    self.view.backgroundColor = [UIColor whiteColor];
    __weak __typeof__(self) weakSelf = self;
    
    [self.view addSubview:self.labelOne];
    [self.labelOne mas_makeConstraints:^(MASConstraintMaker *make) {
        make.left.mas_equalTo(0);
        make.top.mas_equalTo(100);
    }];
    
    [self.view addSubview:self.labelTwo];
    [self.labelTwo mas_makeConstraints:^(MASConstraintMaker *make) {
        make.left.equalTo(weakSelf.labelOne.mas_right);
        make.top.mas_equalTo(100);
    }];
    
    [self.view addSubview:self.labelThree];
    [self.labelThree mas_makeConstraints:^(MASConstraintMaker *make) {
        make.left.equalTo(weakSelf.labelTwo.mas_right);
        make.top.mas_equalTo(100);
        make.right.equalTo(weakSelf.view.mas_right);
    }];
    
    [self.view addSubview:self.qrCodeImgView];
    self.qrCodeImgView.frame = CGRectMake(([UIScreen mainScreen].bounds.size.width - 129) / 2, 240, 129, 129);
    
    [self.view addSubview:self.signLabel];
    self.signLabel.frame = CGRectMake([UIScreen mainScreen].bounds.size.width - 170, 400, 150, 30);
}

- (void)setDataModel:(DMModel *)dataModel
{
    self.labelOne.text = dataModel.oneStr;
    self.labelTwo.text = dataModel.twoStr;
    self.labelThree.text = dataModel.threeStr;
}

#pragma mark - getter and setter
- (UILabel *)labelOne
{
    if (_labelOne == nil) {
        _labelOne = [[UILabel alloc] init];
        _labelOne.backgroundColor = [UIColor clearColor];
        
        // 多大的优先级阻止自己变大 默认250
        [_labelOne setContentHuggingPriority:255 forAxis:UILayoutConstraintAxisHorizontal];
        
        // 多大的优先级阻止自己变小 默认750
        [_labelOne setContentCompressionResistancePriority:750 forAxis:UILayoutConstraintAxisHorizontal];
    }
    
    return _labelOne;
}

- (UILabel *)labelTwo
{
    if (_labelTwo == nil) {
        _labelTwo = [[UILabel alloc] init];
        _labelTwo.backgroundColor = [UIColor clearColor];
        [_labelTwo setContentHuggingPriority:254 forAxis:UILayoutConstraintAxisHorizontal];
        [_labelTwo setContentCompressionResistancePriority:745 forAxis:UILayoutConstraintAxisHorizontal];
    }
    
    return _labelTwo;
}

- (UILabel *)labelThree
{
    if (_labelThree == nil) {
        _labelThree = [[UILabel alloc] init];
        _labelThree.backgroundColor = [UIColor clearColor];
        [_labelThree setContentHuggingPriority:251 forAxis:UILayoutConstraintAxisHorizontal];
        [_labelThree setContentCompressionResistancePriority:740 forAxis:UILayoutConstraintAxisHorizontal];
    }
    
    return _labelThree;
}

- (UIImageView*)qrCodeImgView
{
    if (_qrCodeImgView == nil) {
        _qrCodeImgView = [[UIImageView alloc] init];
        _qrCodeImgView.backgroundColor = [UIColor clearColor];
        _qrCodeImgView.image = [UIImage imageNamed:@"qrcode"];
    }
    
    return _qrCodeImgView;
}

- (UILabel*)signLabel
{
    if (_signLabel == nil) {
        _signLabel = [[UILabel alloc] init];
        _signLabel.backgroundColor = [UIColor clearColor];
        _signLabel.font = [UIFont systemFontOfSize:20];
        _signLabel.text = @"By 点滴86";
        _signLabel.textAlignment = NSTextAlignmentRight;
    }
    
    return _signLabel;
}

@end

示例就到此结束啦