c# - 验证年龄不低于 18

Question

如果此人未满 18 岁，如何显示错误消息？我使用以下代码，但它总是显示年龄无效，即使我输入的日期早于 1995 年。

DateTime dt = DateTime.Parse(dob_main.Text);
DateTime dt_now = DateTime.Now;

DateTime dt_18 = dt.AddYears(-18);

if (dt.Date >= dt_18.Date)
{
    MessageBox.Show("Invalid Birth Day");
}

Answer 1

你应该尝试一下：

var age = GetAge(dt);
if(age < 18)
{
    MessageBox.Show("Invalid Birth Day");
}

int GetAge(DateTime bornDate)
{
    DateTime today = DateTime.Today;
    int age = today.Year - bornDate.Year;
    if (bornDate > today.AddYears(-age)) 
        age--;

    return age;
}

题外话：考虑以这样的方式命名你的变量，这样用户就可以通过阅读它来猜测该变量的意图是什么。dt dob_main离dt_18成为好名字还很远。

Answer 2

DateTime bday = DateTime.Parse(dob_main.Text);
DateTime today = DateTime.Today;
int age = today.Year - bday.Year;
if(age < 18)
{
    MessageBox.Show("Invalid Birth Day");
}

Answer 3

DateTime dt = DateTime.Parse(dob_main.Text);
DateTime dt_now = DateTime.Now;

DateTime dt_18 = dt.AddYears(18); //here add years, not subtract

if (dt_18.Date >= dt_now.Date) //here you want to compare dt_now
{
    MessageBox.Show("Invalid Birth Day");
}

Answer 4

DateTime? BirthDate = DateTime.Parse(dob_main.Text);

if (BirthDate < DateTime.Now.AddYears(-18))
{
  MessageBox.Show("Invalid Birth Day");
}

Answer 5

可以通过在解析日期后简单地使用它来实现这一点：

private static bool GreaterThan18(DateTime bornIn)
{
    return (bornIn.AddYears(18) >= DateTime.Now);    
}

Answer 6

尝试这个：

private static int CalculateAge(DateTime dateOfBirth) 
{ 
   int age = 0;
   age = DateTime.Now.Year - dateOfBirth.Year;
   if (DateTime.Now.DayOfYear < dateOfBirth.DayOfYear) 
     age = age - 1;

   return age;
}

参考：https ://naveed-ahmad.com/2010/01/08/calculating-age-from-date-of-birth-c/

Answer 7

尝试这个：

DateTime birthDate = DateTime.Parse(dob_main.Text);

if (IsAgeLessThan18Years(birthDate))
{
    MessageBox.Show("Invalid Birth Day");
}

bool IsAgeLessThan18Years(DateTime birthDate)
        {
            if (DateTime.Now.Year - birthDate.Year > 18)
            {
                return false;
            }
            else if (DateTime.Now.Year - birthDate.Year < 18)
            {
                return true;
            }
            else //if (DateTime.Now.Year - birthDate.Year == 18)
            {
                if (birthDate.DayOfYear < DateTime.Now.DayOfYear)
                {
                    return false;
                }
                else if (birthDate.DayOfYear > DateTime.Now.DayOfYear)
                {
                    return true;
                }
                else //if (birthDate.DayOfYear == DateTime.Now.DayOfYear)
                {
                    return false;
                }
            }
        }

Answer 8

用这种方式简单

DateTime BirthDate   = DateTime.Parse(dob_main.Text);
DateTime CurrentDate = DateTime.Today;
int Age = CurrentDate.Year - BirthDate.Year;
if(Age < 18)
{
    MessageBox.Show("Invalid Birth Day");
}