java - My Android app crashes when I use method from MainActivity in an other Activity -

i have 2 activities mainactivity , additem

in mainactivity have method:

public void updateui() {     helper = new taskdbhelper(mainactivity.this);     sqlitedatabase sqldb = helper.getreadabledatabase();     cursor cursor = sqldb.query(taskcontract.table,             new string[]{taskcontract.columns._id, taskcontract.columns.task},             null,null,null,null,null);      listadapter = new simplecursoradapter(             this,             r.layout.task_view,             cursor,             new string[] { taskcontract.columns.task},             new int[] { r.id.tasktextview},             0     );      listview listview = (listview)findviewbyid(r.id.list);     listview.setadapter(listadapter);  } 

it updates tasklist on mainscreen.

but when use updateui(); in additem, on saving task returns app crashes en restarts itself.

as error got this:

caused by: java.lang.nullpointerexception: attempt invoke virtual method 'void android.widget.listview.setadapter(android.widget.listadapter)' on null object reference

this code use updateui() in additem:

public void saveitem(view view){     edittext edittext = (edittext)findviewbyid(r.id.edittext);     string task = edittext.gettext().tostring();     log.d("additem", task);      helper = new taskdbhelper(additem.this);     sqlitedatabase db = helper.getwritabledatabase();     contentvalues values = new contentvalues();      values.clear();     values.put(taskcontract.columns.task, task);      db.insertwithonconflict(taskcontract.table, null, values,             sqlitedatabase.conflict_ignore);        updateui();       finish(); } 

could me problem?

thanks in advance,

kind regards, selin

your listview null , when call other activity [when mainactivity paused/stopped] doing null.setadapter causing crash.

you should post sort of event mainactivity , update list/adapter when mainactivity resumes. or can refresh/update adapter in oncreate/onresume of mainactivity.