MySqlConnection.StateChange永远不会抓取

MySqlConnection。StateChange有用吗?

我有以下代码:

conn.StateChange += ConnectionStateChanged;
private void ConnectionStateChanged(Object sender, StateChangeEventArgs e) {
    switch (e.CurrentState) {
    // is never equal to Fetching
    }
}
public DataTable Query(string query) {
    DataTable dt = new DataTable();
    using (MySqlDataAdapter a = new MySqlDataAdapter(query, conn)) {
        try {
            a.SelectCommand.CommandTimeout = 5;
            a.Fill(dt);
        } catch {
            return null;
        }
    }
    return dt;
}

为什么connectionstatechange永远不会被ConnectionState调用。抓取还是connectionstate。正在执行?