设置label约束的优先级

//横向设置label的优先级
//1. 抗拉伸（优先级越高，越不容易被拉伸）
[label_1 setContentHuggingPriority:UILayoutPriorityDefaultLow
                                          forAxis:UILayoutConstraintAxisHorizontal];
[label_2 setContentHuggingPriority:UILayoutPriorityRequired
                                          forAxis:UILayoutConstraintAxisHorizontal];
//2. 抗压缩（优先级越高，越不容易被压缩）
[label_1 setContentCompressionResistancePriority:UILayoutPriorityDefaultLow
                                                        forAxis:UILayoutConstraintAxisHorizontal];
[label_2 setContentCompressionResistancePriority:UILayoutPriorityRequired
                                                        forAxis:UILayoutConstraintAxisHorizontal];