- (void)addLabelConstraint{        [self.nameLabel setTranslatesAutoresizingMaskIntoConstraints:NO];        [self addConstraint:[NSLayoutConstraint constraintWithItem:self.nameLabel attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.contentView attribute:NSLayoutAttributeWidth multiplier:1 constant:0]];        [self addConstraint:[NSLayoutConstraint constraintWithItem:self.nameLabel attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:self.contentView attribute:NSLayoutAttributeHeight multiplier:1 constant:-20]];        [self addConstraint:[NSLayoutConstraint constraintWithItem:self.nameLabel attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.contentView attribute:NSLayoutAttributeCenterX multiplier:1 constant:0]];        [self addConstraint:[NSLayoutConstraint constraintWithItem:self.nameLabel attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.contentView attribute:NSLayoutAttributeCenterY multiplier:1 constant:0]];}

使用 比较方便。