c# 变量 scope

Question

All,

I'm having some problems with the scope of SqlConnection RTTConn.

My code is as follows:

namespace RTT_API
{
    public partial class Request : Form
    {
        private static readonly HttpClient client = new HttpClient();
        private static SqlConnection RTTConn;

        public Request()
        {
            InitializeComponent();
        }



        private void Request_Load(object sender, EventArgs e)
        {

            string connString = @""; << I removed the connection string just for this post

        option 1
            SqlConnection RTTConn = new SqlConnection(connString);
        
        option 2            

        RTTConn.ConnectionString = connString; << "Object reference not set to an instance of an object"
            RTTConn.Open();
            
        }

        private void cmbRefresh_Click(object sender, EventArgs e)
        {
            MessageBox.Show(RTTConn.State.ToString()); << Option 1 - "Object reference not set to an instance of an object"
        ProcessRepositories();
        }

    }

}

If I use option 1 then I get the error in the error in cmbRefresh. I've think I've created two instances of the variable - one at the class level and one in the request_load code? Therefore the one at the class level hasn't had an object assigned to it?

If I use option 2 then I get the error in request_load. I think this is because I haven't created the object?

I would appreciate help with two questions?:

1. Is my understanding above correct?
2. Which is the best way to correct it? I could change the class level declaration to:

SqlConnection RTTConn = new SqlConnection("ConnectionString");

However I don't know if that's the correct way?

Answer 1

The answers from Klaus and Damien_The_Unveliever are both correct. I can't accept them as they are comments so I'm adding an answer referencing them.