Visual C# - Error: 'System.NullReferenceException' occurred in WindowsFormsApplication2.exe -

getting error, did research cant fix it, if can me:

the error:

an unhandled exception of type 'system.nullreferenceexception' occurred in windowsformsapplication2.exe

additional information: object reference not defined instance of object.

it happens on con.open();

my code:

    using system; using system.collections.generic; using system.componentmodel; using system.data; using system.drawing; using system.linq; using system.text; using system.threading.tasks; using system.windows.forms; using system.data.sql; using system.data.sqlclient;  namespace windowsformsapplication2     {             public partial class form1 : form             {                 sqlconnection con;                 sqldataadapter adap;                 dataset ds;      public form1()     {         initializecomponent();     }      private void button1_click(object sender, eventargs e)     {         adicionarfornecedor add = new adicionarfornecedor();         add.showdialog();     }      private void button3_click(object sender, eventargs e)     {         }      private void form1_load(object sender, eventargs e)     {         try         {             sqlconnection con;             sqldataadapter adap;             dataset ds;             con = new sqlconnection();             con.connectionstring = (@"data source=(localdb)\v11.0;attachdbfilename=c:\users\duarte\documents\visual studio 2013\projects\windowsformsapplication2\windowsformsapplication2\papploran.mdf;integrated security=true;connect timeout=30");             con.open();             adap = new sqldataadapter("select * pagamentos", con);             ds = new system.data.dataset();             adap.fill(ds, "p");             datagridview1.datasource = ds.tables[0];         }         catch(exception ex)         {             messagebox.show("erro\n" + ex.message, "error",messageboxbuttons.ok,messageboxicon.error);          }           }      private void button4_click(object sender, eventargs e)     {             adicionarpagamento add2 = new adicionarpagamento();             add2.showdialog();     }      private void button6_click(object sender, eventargs e)     {             verfornecedores add = new verfornecedores();             add.showdialog();     }      private void button5_click(object sender, eventargs e) {         foreach (datagridviewrow item in this.datagridview1.selectedrows)          {              datagridview1.rows.removeat(item.index);          } }      private void search()     {      con.open();         sqlcommand cmd = con.createcommand();         cmd.commandtype = commandtype.text;         cmd.commandtext = "select * pagamentos name ('" + textbox1.text + "%')";         cmd.executenonquery();         datatable dt = new datatable();         sqldataadapter da = new sqldataadapter(cmd);         da.fill(dt);         datagridview1.datasource = dt;          con.close();     }     private void textbox1_textchanged (object sender, eventargs e)     {         search();       }      private void button2_click(object sender, eventargs e)     {      }     }     } 

i want make search in real time write letter program shows the data beginning letter.

you creating new reference connection object in form1_load. try in form_load method:

    try     {          sqldataadapter adap;         dataset ds;         this.con = new sqlconnection();         this.con.connectionstring = (@"data source=(localdb)\v11.0;attachdbfilename=c:\users\duarte\documents\visual studio 2013\projects\windowsformsapplication2\windowsformsapplication2\papploran.mdf;integrated security=true;connect timeout=30");         this.con.open();         adap = new sqldataadapter("select * pagamentos", con);         ds = new system.data.dataset();         adap.fill(ds, "p");         datagridview1.datasource = ds.tables[0];     }     catch(exception ex)     {         messagebox.show("erro\n" + ex.message, "error",messageboxbuttons.ok,messageboxicon.error);      } 

or create new instance in search method.