如何在C＃中将dateTimePickerValue设置为null或为空

Question

I have a windows form of controls combobox and datetimepicker.. I have given null or empty to combobox in page load.. so combobox shows empty intially while loading database values to it in windows form.. but the problem is because of the datetimepicker is not kept to null or empty my form is showing message box as "the day is already existed" before form is desplaying..here my code follows

I want to show that message after combobox value is selected..

    try
       {
           ConnectionStringSettings consettings = ConfigurationManager.ConnectionStrings["attendancemanagement"];
           string connectionString = consettings.ConnectionString;
           SqlConnection cn = new SqlConnection(connectionString);
           cn.Open();
           SqlCommand cmd = new SqlCommand("select employee_id,employee_name from Employee_Details", cn);


           SqlDataReader dtr;
           dtr = cmd.ExecuteReader();
           DataTable dt = new DataTable();


           dt.Columns.Add("employee_id", typeof(string));
           dt.Columns.Add("employee_name", typeof(string));
           dt.Load(dtr);



           comboBox1.DisplayMember = "employee_id";
           comboBox1.DisplayMember = "employee_name";
           comboBox1.DataSource = dt;

           comboBox1.SelectedItem = null;
           if(comboBox1.SelectedItem == null)
           {
               txtemployeeid.Text = "";
               txtemployeename.Text = "";

           }

           cn.Close();
       }

       catch (Exception e1)
       {
           MessageBox.Show(e1.Message);

       }

  private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {

        ConnectionStringSettings consettings = ConfigurationManager.ConnectionStrings["attendancemanagement"];
        string connectionString = consettings.ConnectionString;
        SqlConnection cn = new SqlConnection(connectionString); 
        cn.Open();
        try
        {
            SqlCommand cmd = new SqlCommand("select employee_id,Employee_name from Employee_Details where employee_name=('" + comboBox1.Text + "')", cn);
            SqlDataReader dtr;

             dtr = cmd.ExecuteReader();
           if (dtr.Read())
            {


                string employee_id = (string)dtr["employee_id"];
                string employee_name = (string)dtr["employee_name"];
                txtemployeeid.Text = employee_id;
                txtemployeename.Text = employee_name;
                dtr.Close();
            }

        }
        catch (Exception e1)
        {
            MessageBox.Show(e1.Message);
        }
        if (comboBox1.SelectedItem != null)
        {
            try
            {

                string dtp = dateTimePicker1.Value.ToString("dd/MM/yyyy");
                SqlCommand cmd1 = new SqlCommand("select date from dailyattendance where date=('" + dtp + "') and employee_id='" + txtemployeeid.Text + "' and empployee_name='" + txtemployeename.Text + "' ", cn);
                SqlDataReader dtr1;
                dtr1 = cmd1.ExecuteReader();
                if (dtr1.Read())
                {
                    string date = (string)dtr1["date"];
                    if (dtp == date)
                    {
                        MessageBox.Show("this day is already existed");
                    }
                }
                dtr1.Close();
            }

            catch (Exception e1)
            {
                MessageBox.Show(e1.Message);
            }
        }

        cn.Close();
    }

can any one solve it please..Thanx in advance

Answer 1

您可以简单地使用dtr.Text =“”;