在C＃WPF中添加子例程来处理连接字符串的正确方法是什么？

Question

I have a app.config and a connection string that works perfectly.

App.config

  <connectionStrings>
    <add name="MyConnectionString"
         connectionString="Integrated Security=SSPI;Persist Security Info=False;Initial Catalog=myDatabaseC;Data Source=agent_edx44-PC;"
         providerName="System.Data.SqlClient"/>
  </connectionStrings>

My Form

private void btnSave_Click(object sender, RoutedEventArgs e)
{
    SqlConnection con = new SqlConnection();
    con.ConnectionString = ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;         
    con.Open();
    SqlCommand cmd = new SqlCommand("uspINSERT",con);
    cmd.CommandType = CommandType.StoredProcedure;
    cmd.Parameters.AddWithValue("@FirstName", txtFirstName.Text);
    .....some code
}

private void bindDataGrid()
{
    SqlConnection con = new SqlConnection();
    con.ConnectionString = ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;
    con.Open();
    SqlCommand cmd = new SqlCommand("uspSELECTALL",con);
    cmd.Connection = con;
   ...some code

}

My problem is I want to put this line of code inside a subroutine so that I can call it in any methods.

SqlConnection con = new SqlConnection();
con.ConnectionString = ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;

Here is what i have done so far:

private void MyConnection()
{
    SqlConnection con = new SqlConnection();
    con.ConnectionString = ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;
}
private void btnSave_Click(object sender, RoutedEventArgs e)
{
    MyConnection()
    con.Open();
    SqlCommand cmd = new SqlCommand("uspINSERT",con);
    cmd.CommandType = CommandType.StoredProcedure;
    cmd.Parameters.AddWithValue("@FirstName", txtFirstName.Text);
    .....some code
}

But it has an error saying that:

The name 'con' does not exist in the current context

Answer 1

Here's how you should write those first two methods:

private void btnSave_Click(object sender, RoutedEventArgs e)
{
    using (SqlConnection con = new SqlConnection())
    {
        con.ConnectionString = ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;
        con.Open();
        using (SqlCommand cmd = new SqlCommand("uspINSERT", con))
        {
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.AddWithValue("@FirstName", txtFirstName.Text);
            //.....some code
        }
    }
}

private void bindDataGrid()
{
    using (SqlConnection con = new SqlConnection())
    {
        con.ConnectionString = ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;
        con.Open();
        using (SqlCommand cmd = new SqlCommand("uspSELECTALL", con))
        {
            cmd.Connection = con;
            //...some code
        }
    }
}

Now,to get your new code to work you need to return the connection from the MyConnection method:

private SqlConnection MyConnection()
{
    SqlConnection con = new SqlConnection();
    con.ConnectionString = ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;
    return con;
}

private void btnSave_Click(object sender, RoutedEventArgs e)
{
    using (SqlConnection con = MyConnection())
    {
        con.Open();
        using (SqlCommand cmd = new SqlCommand("uspINSERT", con))
        {
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.AddWithValue("@FirstName", txtFirstName.Text);
            //.....some code
        }
    }
}

Now, I would go one step further and do this:

private void RunSqlCommand(string cmdText, Action<SqlConnection, SqlCommand> execute)
{
    using (SqlConnection con = new SqlConnection())
    {
        con.ConnectionString = ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;
        con.Open();
        using (SqlCommand cmd = new SqlCommand(cmdText, con))
        {
            cmd.Connection = con;
            execute(con, cmd);
        }
    }
}

Now your btnSave_Click method can become this:

private void btnSave_Click(object sender, RoutedEventArgs e)
{
    RunSqlCommand("uspINSERT", (con, cmd) =>
    {
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Parameters.AddWithValue("@FirstName", txtFirstName.Text);
        //.....some code
    });
}

Answer 2

Change your MyConnection method to this, it returns a SqlConnection:

private SqlConnection MyConnection()
{
    SqlConnection con = new SqlConnection();
    con.ConnectionString = ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;
    return con;
}

This is how to use:

using (var con = MyConnection()) 
{
   //your code
}

using block will dispose your DB connection after you have done with it.