Object reference not set to an instance of an object c# opening new form -

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• what nullreferenceexception, , how fix it? 29 answers

1. ask user username , password
2. on click button checks database connected username , password,
3. when correct stores it's id number in variable, default variable 0.
4. then run if-statement, if id >= 0, needs open form. if not displays error message.

messagebox in first if case displays correct id (1,2,3 whatever) on form3, simple textbox1.text = "hi"; gives me error:

object reference not set instance of object c#. , displays textbox line.

    int idnumber = 0;          sqlcommand datacommand = new sqlcommand(" select id leden [username]='" + username_txt.text + "' , [password]='" + password_txt.text + "'", sc);         sc.open();         idnumber = convert.toint32(datacommand.executescalar());         sc.close();          if (idnumber >= 1)         {             messagebox.show("logged in, welcome id number:" + idnumber, "test");             form3 f3 = new form3(idnumber);             f3.show();                          }         else         {             messagebox.show("wrong username and/or password");         }  } 

form3:

public form3(int _idnumber) {     int idnumber = _idnumber;     textbox1.text = "hi"; } 

of course textbox test, show doesn't matter textbox use, gives me error. yes, still use unecrypted passwords, don't know how yet

you have not initialized components on form yet. add

initializecomponent(); 

in beginning of contructor.