1.自適應寬度
前提不需要設置label的寬度
[yourLabel setContentHuggingPriority:UILayoutPriorityRequired forAxis:UILayoutConstraintAxisHorizontal];
2.label多行自適應高度
label.preferredMaxLayoutWidth = width;//給一個maxWidth
[label setContentHuggingPriority:UILayoutPriorityRequired forAxis:UILayoutConstraintAxisVertical];//設置huggingPriority
label.numberOfLines = 0;//設置換行