我的 If 语句中的 C# 语法问题

Question

我的 if 语句有问题，希望有人来研究一下我认为我的主要问题在于:

(string.IsNullOrWhiteSpace(txtFirstName.Text) || string.IsNullOrWhiteSpace(txtLastName.Text) || string.IsNullOrWhiteSpace(txtEmail.Text) || string.IsNullOrWhiteSpace(txthotel.Text))

我想如果所有语句都是假的，它应该执行 mysql 命令(PS 它目前正在工作，但语法错误。)

        if (appointment.CheckState == CheckState.Checked)
        {
            if (string.IsNullOrWhiteSpace(txtFirstName.Text))
            {
                txtFirstName.BackColor = Color.Red;
                MessageBox.Show("Please enter first name!");
            }
            else
            {
                txtFirstName.BackColor = Color.White;
            }
            if (string.IsNullOrWhiteSpace(txtLastName.Text))
            {
                txtLastName.BackColor = Color.Red;
                MessageBox.Show("Please enter last name!");
            }
            else
            {
                txtLastName.BackColor = Color.White;
            }

            if (string.IsNullOrWhiteSpace(txtEmail.Text))
            {
                txtEmail.BackColor = Color.Red;
                MessageBox.Show("Please enter Email!");
            }
            else
            {
                txtEmail.BackColor = Color.White;
            }

            if (string.IsNullOrWhiteSpace(txthotel.Text))
            {
                txthotel.BackColor = Color.Red;
                MessageBox.Show("Please enter a valid hotel!");
            }
            else
            {
                txthotel.BackColor = Color.White;    
            }



            if (string.IsNullOrWhiteSpace(txtFirstName.Text) || string.IsNullOrWhiteSpace(txtLastName.Text) || string.IsNullOrWhiteSpace(txtEmail.Text) || string.IsNullOrWhiteSpace(txthotel.Text)) 
            {

            }
            else
            {
                ///register client
                connect.Open();
                MySqlCommand command = new MySqlCommand("Insert into client (firstName,lastName,Nationality,mobile,email,budget,comments) value(@firstName,@lastName,@Nationality,@mobile,@email,@budget,@comments)", connect);
                command.Parameters.AddWithValue("@firstName", txtFirstName.Text);
                command.Parameters.AddWithValue("@lastName", txtLastName.Text);
                command.Parameters.AddWithValue("@Nationality", txtNationality.Text);
                command.Parameters.AddWithValue("@mobile", txtMobile.Text);
                command.Parameters.AddWithValue("@email", txtEmail.Text);
                command.Parameters.AddWithValue("@budget", int.Parse(txtBudget.Text));
                command.Parameters.AddWithValue("@comments", txtComments.Text);


                command.ExecuteNonQuery();
                connect.Close();

                loadclient();



                ///register appointment
                connect.Open();
                command = new MySqlCommand("Insert into appointment(Hotel,Roomnumber,AppointmentDate,Appointmenttime,ConfirmBy,Propertytype,Bedrooms,Purpose,Interestedin,Departuredate) value(@Hotel,@Roomnumber,@AppointmentDate,@Appointmenttime,@ConfirmBy,@Propertytype,@Bedrooms,@Purpose,@Interestedin,@Departuredate)", connect);
                command.Parameters.AddWithValue("@Hotel", txthotel.Text);
                command.Parameters.AddWithValue("@Roomnumber", int.Parse(txtRoomNumber.Text));
                command.Parameters.AddWithValue("@AppointmentDate", dateTimePicker2.Value.Date);
                command.Parameters.AddWithValue("@Appointmenttime", cmbTimeApp.Text);
                command.Parameters.AddWithValue("@ConfirmBy", cmbConfirm.Text);
                command.Parameters.AddWithValue("@Propertytype", cmbpropertytype.Text);
                command.Parameters.AddWithValue("@Bedrooms", cmbBedRoom.Text);
                command.Parameters.AddWithValue("@Purpose", cmbPurpose.Text);
                command.Parameters.AddWithValue("@Interestedin", cmbIntrestedIn.Text);
                command.Parameters.AddWithValue("@Departuredate", dateTimePicker3.Value.Date);

                command.ExecuteNonQuery();
                connect.Close();

                MessageBox.Show("Appointment registered!");
            }



        }

Answer 1

显然是该类型的任何逻辑表达式:

if  (Condition1 || Condition2 || Condition3 || ....) 
{
    DoA();   
}
else
{
    DoB();
}

可以转化为:

if  (!Condition1 && !Condition2 && !Condition3 && ....) 
{
    DoB();   
}
else
{
    DoA();
}

这会解决你的问题，但代码的可读性仍然值得怀疑

if (!string.IsNullOrWhiteSpace(txtFirstName.Text) &&
    !string.IsNullOrWhiteSpace(txtLastName.Text) &&
    !string.IsNullOrWhiteSpace(txtEmail.Text) && 
    !string.IsNullOrWhiteSpace(txthotel.Text))
{
    //...
} 

讨厌!

我们如何改进这一点？有时简单地使用辅助局部变量会使您的代码更易于阅读；它突出了代码的语义并隐藏了机制。本地人非常便宜(甚至免费)，使用它们!

考虑以下方法:

var isValidFirstName = !string.IsNullOrWhiteSpace(txtFirstName.Text)
var isValidLastName = !string.IsNullOrWhiteSpace(txtLastName.Text)
var isValidEmail = !string.IsNullOrWhiteSpace(txtEmail.Text)
var isValidHotel = !string.IsNullOrWhiteSpace(txthotel.Text))

现在您的 if 语句如下所示:

if (isValidFirstName &&
    isValidLastName &&
    isValidEmail && 
    isValidHotel)
{
    //...
}

这样读起来不是更好吗？

但为什么要停在这里呢？我们不能抽象出整个客人信息验证吗？我们当然可以:

public static bool IsValidGuestInfo(string firstName, string lastName, string email, string hotel)
{
     var isValidFirstName = !string.IsNullOrWhiteSpace(txtFirstName.Text)
     var isValidLastName = !string.IsNullOrWhiteSpace(txtLastName.Text)
     var isValidEmail = !string.IsNullOrWhiteSpace(txtEmail.Text)
     var isValidHotel = !string.IsNullOrWhiteSpace(txthotel.Text))

     return isValidFirstName && isValidLastName && isValidEmail && isValidHotel;
}

现在您的 if 语句很简单:

 if (IsValidGuestInfo(firstName, lastName, email, hotel))
 {
     //...
 }

现在读起来更好了，语义清晰了，而且使用的机制也没有阻碍。此外，启动时，如果您需要在代码中的其他任何地方验证 guest 信息，则无需复制代码。