C# Windows Form set value of selectedIndex comobox

Question

after searching on this site i can't find the correct solution and need help.

I'm trying to modify a field of an user (I simulate that user wants to change their city)

I have a table like this:

+---------+---------------------+
| id_city | name                |
+---------+---------------------+
|       1 | India               |
|       2 | Irland              |
|       3 | France              |
+---------+---------------------+

And when I launch the query and I get the result I need is like that:

+---------+---------------------+
| id_city | name                |
+---------+---------------------+
|       3 | France              |
|       1 | India               |
|       2 | Irland              |
+---------+---------------------+

And in my C# code when initialize the windows forms I fill the combobox:

modifyCityUserComboBox.ValueMember = "id_city";
modifyCityUserComboBox.DisplayMember = "name";
modifyCityUserComboBox.DataSource = dataTable;

Then I try to put in the combobox the city that user have, but in this part I have the problem. When I do:

modifyCityUserComboBox.SelectedIndex = userDto.GetIdCity();

(supose that India is the original city of the user and wants to change it)

I have this error = "Invalid argument= The value of '1' is not valid for 'SelectedIndex. Parameter name= SelectedIndex".

I've been discovered that combobox start selectedIndex in 0 and if I don't order the cities I only need do:

modifyCityUserComboBox.SelectedIndex = userDto.GetIdCity() - 1;

With this "trick" the IdCity it's 0 and combobox accept it but I don't want do it that way. I want show the cities ordered.

I've tried set True the Sort combobox property and not order the cities in the mysql query but I get the same error...

Anyone know how can I do it? Thanks!

Answer 1

use modifyCityUserComboBox.SelectedValue=userDto.GetIdCity();

Answer 2

I don't know how did you set up your classes, but this is how I've done it and it works. First I insert all cities from database to ComboBox list inside Form1 constructor. After that you can press button1 on Form1 to change the city depending on the User inside button1_Click event. Let me demonstrate you the Form1:

---

Main method:

public Form1()
{
    InitializeComponent();

    List<DataTable> dataTable = new List<DataTable>();

    string path = @"server=.\sqlexpress;database=Cities;integrated Security=True;";

    using (SqlConnection con = new SqlConnection(path))
    {
        SqlCommand cmd = con.CreateCommand();
        cmd.CommandText = "select id_city, name from city order by name";
        try
        {
            con.Open();

            using (SqlDataReader dr = cmd.ExecuteReader())
            {
                while (dr.Read())
                {
                    dataTable.Add(new DataTable()
                    {
                        id_city = (int)dr["id_city"]
                       ,name = dr["name"] as string
                    });
                }
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message, "Error");
        }
    }

    BindingSource bs = new BindingSource() { DataSource = dataTable };
    comboBox1.ValueMember = "id_city";
    comboBox1.DisplayMember = "name";
    comboBox1.DataSource = bs;
}

---

DataTable class:

class DataTable
{
    public int id_city { get; set; }
    public string name { get; set; }
}

---

button1_Click event:

private void button1_Click(object sender, EventArgs e)
{
    User user = new User("India");

    var myarr = comboBox1.Items.OfType<DataTable>().ToArray();

    foreach (var item in myarr)
    {
        if (item.name.Equals(user.city))
        {
            comboBox1.SelectedItem = item;
            break;
        }
    }
}

---

User class:

class User
{
    public string city { get; set; }

    public User(string str)
    {
        city = str;
    }
}

---

Feel free to insert more cities in your database and change the country of User inside button1_Click event. Modify it the way you like, hope this helps!