How to show listbox item in textBox using data from local database in C# -

hi im new programming , working on project lets user enter registration data local database using textboxes. code works adding items database , after press "show_users" button displays them in listbox_users listbox.

my problem when choose name listbox_users should dislay data selected user in upper textbox'es used enter data in first place using event created listbox_users, im getting error "can't read data database closed".

namespace userform { public partial class form1: form {     sqlcedatareader rdr;      public form1()     {         initializecomponent();     }      // code between...      private void button_showusers_click(object sender, eventargs e) //code shows users in listbox     {          var dt = new datatable();         string connectionstring2 = @"data source=mydatabase;password=xxxxxx;";          using (var cn = new sqlceconnection(connectionstring2))         using (var cmd = new sqlcecommand("select * users", cn))         {             cn.open();              using (var reader = cmd.executereader())             {                 dt.load(reader);                 var results = (from row in dt.asenumerable()                                select new                                {                                    //userid = row.field<int>("id"),                                    firstname = row.field<string>("firsname"),                                    lastname = row.field<string>("lastname"),                                    fullname = row.field<string>("firstname") + " " + row.field<string>("lastname")                                }).tolist();                  listbox_users.datasource = results;                 listbox_users.displaymember = "fullname";                  rdr = cmd.executereader();                 }             }         }      //i made event listbox_users:      private void listbox_users_selectedindexchanged(object sender, eventargs e)      //event code should show listbox selected data in textboxes     {                     if (listbox_inimesed.selecteditem != null && rdr != null)         {             try             {                 if (rdr.read())                 {                      textbox1_firstname.text = rdr.getstring(1);                     textbox2_lastname.text = rdr.getstring(2);                     textbox3_email.text = rdr.getstring(3);                     textbox4_address.text = rdr.getstring(4);                     datetimepicker1.value = rdr.getdatetime(5);                     richtextbox_info.text = rdr.getstring(6);                 }                 else messagebox.show("object not found");             }                         {                 rdr.close();             }         }     } } 

the connection reader using dependent on has been closed in button_showusers_click event.

it not practice try share connections , datareaders across events. result in open connections not disposed of correctly. better practice have creation of connection, command, , datareader take place in each event method. using "using" statement closed , disposed of correctly in each method. can remove class level variable "rdr".

namespace userform {     public partial class form1 : form     {         const string connectionstring2 = @"data source=mydatabase;password=xxxxxx;";          public form1()         {             initializecomponent();         }          // code between...          private void button_showusers_click(object sender, eventargs e) //code shows users in listbox         {             var dt = new datatable();              using (var cn = new sqlceconnection(connectionstring2))             using (var cmd = new sqlcecommand("select * users", cn))             {                 cn.open();                  using (var reader = cmd.executereader())                 {                     dt.load(reader);                     var results = (from row in dt.asenumerable()                                    select new                                    {                                        //userid = row.field<int>("id"),                                        firstname = row.field<string>("firsname"),                                        lastname = row.field<string>("lastname"),                                        fullname = row.field<string>("firstname") + " " + row.field<string>("lastname")                                    }).tolist();                      listbox_users.datasource = results;                     listbox_users.displaymember = "fullname";                 }             }         }      //i made event listbox_users:          private void listbox_users_selectedindexchanged(object sender, eventargs e)         //event code should show listbox selected data in textboxes         {             if (listbox_inimesed.selecteditem != null)             {                 using (var cn = new sqlceconnection(connectionstring2))                 using (var cmd = new sqlcecommand("select * users", cn))                 {                     cn.open();                      using (var reader = cmd.executereader())                     {                         if (reader.read())                         {                             textbox1_firstname.text = reader.getstring(1);                             textbox2_lastname.text = reader.getstring(2);                             textbox3_email.text = reader.getstring(3);                             textbox4_address.text = reader.getstring(4);                             datetimepicker1.value = reader.getdatetime(5);                             richtextbox_info.text = reader.getstring(6);                         }                         else messagebox.show("object not found");                     }                 }             }         }     } }