InvalidOperationException The connection was not closed. The connection's current state is open

Question

Why does this code throw an Invalid Operation Exception?

private SqlCommand cmd; // initialized in the class constructor

public void End(string spSendEventNotificationEmail) {
  try {
    cmd.CommandText = spSendEventNotificationEmail;
    cmd.Parameters.Clear();
    cmd.Parameters.Add("@packetID", SqlDbType.Int).Value = _packetID;
    cmd.Parameters.Add("@statusID", SqlDbType.Int).Value = _statusID;
    cmd.Parameters.Add("@website", SqlDbType.NVarChar, 100).Value = Tools.NextStep;
    cmd.Connection.Open();
    cmd.ExecuteNonQuery();
  } finally {
    cmd.Connection.Close();
    cmd.Parameters.Clear();
    cmd.Dispose();
  }
  endCall = true;
}

Answer 1

You're trying to open a connection which is already open, this results in exception.

Solution 1 (recommended):

Inspect your code, check all the parts where cmd.Connection connection is opened and ensure that it's always closed properly.

Solution 2 (quick'n'dirty fix):

before line

cmd.Connection.Open();

add the following check/cleanup code:

if (cmd.Connection.State == ConnectionState.Open)
{
    cmd.Connection.Close();
}

Answer 2

There's very little need for keeping the Sql* objects at the class level, especially based on what you're showing. You'll also lose the benefits of connection pooling by attempting to do it yourself.

With this method, you remove the possibility of your error because you're not sharing any objects

private readonly _connectionString = "...";

public void End(string spSendEventNotificationEmail) {
  using(var conn = new SqlConnection(_connectionString))
  using(var cmd = conn.CreateCommand())
  {
    cmd.CommandText = spSendEventNotificationEmail;
    cmd.Parameters.Add("@packetID", SqlDbType.Int).Value = _packetID;
    cmd.Parameters.Add("@statusID", SqlDbType.Int).Value = _statusID;
    cmd.Parameters.Add("@website", SqlDbType.NVarChar, 100).Value = Tools.NextStep;
    conn.Open();
    cmd.ExecuteNonQuery();
  }
  endCall = true;
}