How to enter connection string on runtime? ~ Programming Share

One of the challenging tasks in .NET programming is changing the connection string on runtime. In this post, I will give you the simple step to complete this task.
Step 1: Create a SQL Conneciton form:
On the Solution Explorer panle, right click on your project, select Add->New Item. Select Window Form. Name it SLQConnection, then click OK. Design it as the figure bellow:

Step 2: Create an app.config file
On the Solution Explorer, right click on your project, select Add->New Item. On the dialog appeared, click on Application Configuration File, name it app.config. Click OK
Open app.config file, modifying it as the figure bellow

Step 3: Coding
On the SQLConnection.cs file, add the following code:
        public void updateConfigFile(string con)
        {
            XmlDocument XmlDoc = new XmlDocument();
            //Road the Config file
            XmlDoc.Load(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);
            foreach (XmlElement xElement in XmlDoc.DocumentElement)
            {
                if (xElement.Name == "connectionStrings")
                {
                    //setting the connection string
                    xElement.FirstChild.Attributes[2].Value = con;
                }
            }
            //write the connection string in app.config file
            XmlDoc.Save(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);
        }

Double click on Connect button of the Form created in step 1
Add the following code to the On_Clikc event of the button

                StringBuilder Con = new StringBuilder("Data Source=");
                Con.Append(txtServerName.Text);
                Con.Append(";Initial Catalog=");
                Con.Append(txtDBName.Text);
                Con.Append(";Integrated Security=SSPI;");
                string strCon = Con.ToString();
                updateConfigFile(strCon);

                //create a new connection
                SqlConnection conn = new SqlConnection();
                ConfigurationManager.RefreshSection("connectionStrings");
                conn.ConnectionString = ConfigurationManager.ConnectionStrings["Conn"].ToString();
//get data from a table to test the connection
                SqlDataAdapter da = new SqlDataAdapter("select * from Users", conn);
                DataTable dt = new DataTable();
                da.Fill(dt);
                if (dt.Rows.Count > 0)
                {
                    MessageBox.Show("Connection successful", "Notice", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
                }
                else
                {
                    MessageBox.Show("Connection failed", "Notice", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
                }

To get the connection string on runtime, use the following code
string cnstr = ConfigurationManager.ConnectionStrings["Conn"].ToString();

Now, test it!

Hope this helps!