c# - Connection was not closed. Connection's current state is open -

it gives error connection not closed. connection's current state open. please out code.

  private void combobox1_selectedindexchanged(object sender, eventargs e)     {         sqlconnection con = new sqlconnection(@"data source=.\sqlexpress;attachdbfilename=c:\users\vicky\desktop\gym management system\fitness_club\vicky.mdf;integrated security=true;connect timeout=30;user instance=true");         try         {             con.open();              sqlcommand cmd = new sqlcommand("select * [plan] plantype='" + combobox1.text + "'", con);              sqldatareader dr = cmd.executereader();              while (dr.read())             {                 string amount = dr.getstring(1);                 textbox5.text = amount;              }             con.close();         }          catch(exception ex)         {             messagebox.show(ex.message);         }  } 

you should using using blocks managing objects.

    private void combobox1_selectedindexchanged(object sender, eventargs e)     {         string connstr = @"data source=.\sqlexpress;attachdbfilename=c:\users\vicky\desktop\gym management system\fitness_club\vicky.mdf;integrated security=true;connect timeout=30;user instance=true";         string cmdtext = "select * [plan] plantype=@plantype";          using (sqlconnection con = new sqlconnection(connstr))         using (sqlcommand cmd = con.createcommand())         {             con.open();             cmd.commandtext = cmdtext;             cmd.parameters.addwithvalue("@plantype", combobox1.text);              var reader = cmd.executereader(commandbehavior.singlerow);              if (reader.read())             {                 string amount = reader.getstring(1);                 textbox5.text = amount;             }         }     } 

also note use of parameterized queries avoid sql injection attacks. since expecting 1 value returned, should specify name of column in query , use executescalar instead of reader , while loop. other alternative use commandbehavior.singlerow parameter command, tells command return single row result.

you have cross-threading problem here, , can solve using invoking.

string amount = string.empty; if (reader.read()) {     amount = reader.getstring(1); } if (this.invokerequired)     this.invoke((methodinvoker) delegate { textbox5.text = amount; }); else     textbox5.text = amount; 

another thing note, give controls meaningful names. lot easier debug or understand control named cbx_plantype combobox1, or tbx_planamount rather textbox5.