Question

我的if语句存在问题，希望有人看到它，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它暂时正在工作，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

显然任何类型的逻辑表达式：

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

可以转换为：

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

这可以解决您的问题，但代码可读性仍然可疑

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

呸！

我们如何改善这一点？有时简单地使用辅助局部变量会使代码更容易阅读;它突出了代码的语义并隐藏了机制。当地人非常便宜（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)
{
    //...
}

那不是读得好多了吗？

但为何停在这里？我们不能只抽象整个客户信息验证吗？当然，我们可以：

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;
}

现在你的if声明只是：

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

现在读得更好，语义清晰并且使用的机制不会妨碍。此外，要启动，如果您需要在代码中的任何其他位置验证访客信息，则无需重复代码。

Answer 2

我会将其全部放入if并放弃else部分

if (!string.IsNullOrWhiteSpace(txtFirstName.Text) && !string.IsNullOrWhiteSpace(txtLastName.Text) && !string.IsNullOrWhiteSpace(txtEmail.Text) && !string.IsNullOrWhiteSpace(txthotel.Text)) 
{
    //register client
    connect.Open();
    ...

Answer 3

基本上，这个

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

如果任何操作数为true，则

为true。你把它放到一个空的if和else处理命令。这是正确的，但它过于复杂。你可以这样检查

        if (!(string.IsNullOrWhiteSpace(txtFirstName.Text) || string.IsNullOrWhiteSpace(txtLastName.Text) || string.IsNullOrWhiteSpace(txtEmail.Text) || string.IsNullOrWhiteSpace(txthotel.Text))) 
        {
            ///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 4

Lajos＆＃39;答案很美。我可能想以相反的方式尝试：

    if(string.IsNullOrWhiteSpace(txtFirstName.Text) || string.IsNullOrWhiteSpace(txtLastName.Text) || string.IsNullOrWhiteSpace(txtEmail.Text) || string.IsNullOrWhiteSpace(txthotel.Text)) 
{
   return; //Isn't it short and simple?
   //Or if you want to jump somewhere and not to exit....
   goto dosomething:
}

    dosomething:
    MessageBox.Show("Something is blank! ");

我的If语句中的C＃语法问题

4 个答案: