c# - 运算符 '>='不能应用于 'System.DateTime?'和 'int'类型的操作数

Question

我的代码是这样的，但是我需要验证RemainingDay是否大于10，然后在剩余的几天中不会显示消息框

if (Convert.ToDateTime(dr[0]) == DateTime.Today)
{
    MessageBox.Show("Your trail period is expired. Please purchase this Software.", "SMS");
    Application.Exit();
}
else
{
    newDate = Convert.ToDateTime(dr[0]);
    RemainingDay = newDate.Subtract(TodayDate);

    MessageBox.Show("You have " + RemainingDay.Days + " days Left.", "SMS");
    this.Hide();

    frmMainMenu frm = new frmMainMenu();
    frm.Show();
    frm.lblUser.Text = txtUserName.Text;
}

我尝试了下面的代码:

if (Convert.ToDateTime(dr[0]) == DateTime.Today)
{
    MessageBox.Show("Your trail period is expired. Please purchase this Software.", "SMS");
    Application.Exit();
}
else
{
    newDate = Convert.ToDateTime(dr[0]);
    RemainingDay = newDate.Subtract(TodayDate);

    if (RemainingDay <= 10)
    {
        MessageBox.Show("You have " + RemainingDay.Days + " days Left.", "SMS");
        this.Hide();
    }
    else
    {
        this.Hide();
        frmMainMenu frm = new frmMainMenu();
        frm.Show();
        frm.lblUser.Text = txtUserName.Text;
    }                        
}

上面的代码给我这个错误:

Operator '>=' cannot be applied to operands of type 'System.DateTime?' and 'int'

请帮我。

Answer 1

您的RemainingDay变量是 TimeSpan ，它是给定的DateTime和今天的日期之间的差。您看不到TimeSpan是否小于数字-这没有任何意义。

您想要得到的是日期之间的天数差，TimeSpan保存在 .Days 属性中，这将给您(来自MSDN)

the days component of the time interval represented by the current TimeSpan structure.

所以用那个代替。