iOS-UILabel 的抗拉伸和抗压缩

UIView 中关于 Content Hugging 和 Content Compression Resistance 的方法有如下：

- (UILayoutPriority)contentHuggingPriorityForAxis:(UILayoutConstraintAxis)axis API_AVAILABLE(ios(6.0));
- (void)setContentHuggingPriority:(UILayoutPriority)priority forAxis:(UILayoutConstraintAxis)axis API_AVAILABLE(ios(6.0));

- (UILayoutPriority)contentCompressionResistancePriorityForAxis:(UILayoutConstraintAxis)axis API_AVAILABLE(ios(6.0));
- (void)setContentCompressionResistancePriority:(UILayoutPriority)priority forAxis:(UILayoutConstraintAxis)axis API_AVAILABLE(ios(6.0));

在 Autolayout 优先级的范围是 1 ~ 1000，创建一个约束，默认的优先级是最高的 1000。

Content Hugging Priority

Content Hugging Priority: 该优先级表示一个控件抗被拉伸的优先级。优先级越高，越不容易被拉伸。

使用场景：
当一个视图上有多个 intrinsic content size 的子控件，子视图的总和，不够填充父视图区域时，此属性可以控制优先拉伸哪个视图内容。

Content Compression Resistance Priority

Content Compression Resistance Priority: 该优先级和上面那个优先级相对应，表示一个控件抗压缩的优先级。优先级越高，越不容易被压缩

使用场景：
当一个视图上有多个 intrinsic content size 的子控件，并且子控件可能会超出父视图的区域时，此属性可控制哪些视图被内容被优先压缩，使其不超出父视图区域。

相关代码：

// 抗被拉伸
[self.label setContentHuggingPriority:UILayoutPriorityRequired forAxis:UILayoutConstraintAxisHorizontal];
// 抗被压缩
[self.label setContentCompressionResistancePriority:UILayoutPriorityRequired forAxis:UILayoutConstraintAxisHorizontal];

优先级：

static const UILayoutPriority UILayoutPriorityRequired API_AVAILABLE(ios(6.0)) = 1000; // A required constraint.  Do not exceed this.
static const UILayoutPriority UILayoutPriorityDefaultHigh API_AVAILABLE(ios(6.0)) = 750; // This is the priority level with which a button resists compressing its content.
static const UILayoutPriority UILayoutPriorityDragThatCanResizeScene API_AVAILABLE(macCatalyst(13.0)) = 510; // This is the appropriate priority level for a drag that may end up resizing the window's scene.
static const UILayoutPriority UILayoutPrioritySceneSizeStayPut API_AVAILABLE(macCatalyst(13.0)) = 500; // This is the priority level at which the window's scene prefers to stay the same size.  It's generally not appropriate to make a constraint at exactly this priority. You want to be higher or lower.
static const UILayoutPriority UILayoutPriorityDragThatCannotResizeScene API_AVAILABLE(macCatalyst(13.0)) = 490; // This is the priority level at which a split view divider, say, is dragged.  It won't resize the window's scene.
static const UILayoutPriority UILayoutPriorityDefaultLow API_AVAILABLE(ios(6.0)) = 250; // This is the priority level at which a button hugs its contents horizontally.
static const UILayoutPriority UILayoutPriorityFittingSizeLevel API_AVAILABLE(ios(6.0)) = 50; // When you send -[UIView systemLayoutSizeFittingSize:], the size fitting most closely to the target size (the argument) is computed.  UILayoutPriorityFittingSizeLevel is the priority level with which the view wants to conform to the target size in that computation.  It's quite low.  It is generally not appropriate to make a constraint at exactly this priority.  You want to be higher or lower.

水平or垂直

typedef NS_ENUM(NSInteger, UILayoutConstraintAxis) {
    UILayoutConstraintAxisHorizontal = 0,
    UILayoutConstraintAxisVertical = 1
};

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感谢该篇文章的分享：浅谈 iOS AutoLayout 中 Label 的抗拉伸和抗压缩