sql server - How to properly connect to database in vb -

i need on codes and/or connection.i'm getting error says:

an unhandled exception of type 'system.invalidoperationexception' occurred in system.data.dll

additional information: executereader requires open , available connection. connection's current state closed.

in code:(line 4)

cmd.connection = cn     cmd.commandtext = "select id, lastname, firstname tblmembers id = @id"     cmd.parameters.add(new sqlclient.sqlparameter("@id", sqldbtype.int)).value = dg1.item(0, e.rowindex).value     dr = cmd.executereader     if dr.hasrows()         dr             .read()             txtlname.text = dr("lastname")             txtfname.text = dr("firstname")         end     end if 

but if try open connection. happens.

an unhandled exception of type 'system.invalidoperationexception' occurred in system.data.dll

additional information: connection not closed. connection's current state open.

with code:(line 1)

 cn.open()     cmd.connection = cn     cmd.commandtext = "select id, lastname, firstname tblmembers id = @id"     cmd.parameters.add(new sqlclient.sqlparameter("@id", sqldbtype.int)).value = dg1.item(0, e.rowindex).value     dr = cmd.executereader     if dr.hasrows()         dr             .read()             txtlname.text = dr("lastname")             txtfname.text = dr("firstname")         end     end if 

    dim cn sqlconnection     dim cmd sqlcommand     dim dr sqldatareader     dim connetionstring string     dim process_id string     dim processname string      connetionstring = "data source=servername;initial catalog=databasename;user id=username;password=password"      cn = new sqlconnection(connetionstring)      cn.open()      cmd = new sqlcommand("select process_id,processname  dbo.process_master process_id = @id", cn)      cmd.parameters.add(new sqlclient.sqlparameter("@id", sqldbtype.int)).value = "21"      dr = cmd.executereader      if dr.hasrows()          dr.read()              process_id = dr("process_id")             processname = dr("processname")          end     end if