iOS label通过内容获取高度

+ (CGFloat)cellHeightWithMsg:(NSString *)msg
{
    UILabel *label = [[UILabel alloc] init];
    label.text = msg;
    label.font = [UIFont systemFontOfSize:16];
    label.numberOfLines = 0;
    CGSize size = [label sizeThatFits:CGSizeMake(UIScreenWidth-26, CGFLOAT_MAX)];
    return size.height;
}