sqlite - How to display data from a database android -


this question has answer here:

im trying query, shows error. code

public string c(){      objbd = new bd(ncontext, "laboratorios", null, 1);     db = objbd.getreadabledatabase();     cursor c=db.rawquery("select * laboratorios id = (select max(id) laboratorios);", null);     if(c!=null) {         while (c.movetonext()) {             string ilab = c.getstring(c.getcolumnindex("descripcion"));              //.add(ilab);             return ilab;         }     }     return null; }

this activity want display 

protected void oncreate(bundle savedinstancestate) {     textview lab=(textview)findviewbyid(r.id.lab_con);     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_consulta);     toolbar toolbar = (toolbar) findviewbyid(r.id.toolbar);     setsupportactionbar(toolbar);      conexionbd o1=new conexionbd(this);     o1.c();       lab.settext(o1);      floatingactionbutton fab = (floatingactionbutton) findviewbyid(r.id.fab);     fab.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view view) {             snackbar.make(view, "replace own action", snackbar.length_long)                     .setaction("action", null).show();          }     });         getsupportactionbar().setdisplayhomeasupenabled(true);           /*string texto ="bien";         toast toast = toast.maketext(this, texto, toast.length_long);         toast.show();         intent =new intent(this,labs.class);         startactivity(i);*/  }    public void salir (view view){     string texto ="se ha guardado su registro";     toast toast = toast.maketext(this, texto, toast.length_long);     toast.show();     intent salida=new intent( intent.action_main); //llamando la activity principal     finish();  }

this error

  caused by: java.lang.nullpointerexception: attempt invoke virtual method 'void android.widget.textview.settext(java.lang.charsequence)' on null object reference

im trying in blank activity have error, thank me.

this error

java.lang.runtimeexception: unable start activity componentinfo{com.example.oscar.app/com.example.oscar.app.consulta}: java.lang.nullpointerexception: attempt invoke virtual method 'void android.support.design.widget.floatingactionbutton.setonclicklistener(android.view.view$onclicklistener)' on null object reference @ android.app.activitythread.performlaunchactivity(activitythread.java:2646) @ android.app.activitythread.handlelaunchactivity(activitythread.java:2707) @ android.app.activitythread.-wrap12(activitythread.java) @ android.app.activitythread$h.handlemessage(activitythread.java:1460) @ android.os.handler.dispatchmessage(handler.java:102) @ android.os.looper.loop(looper.java:154) @ android.app.activitythread.main(activitythread.java:6077) @ java.lang.reflect.method.invoke(native method) @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:865) @ com.android.internal.os.zygoteinit.main(zygoteinit.java:755) caused by: java.lang.nullpointerexception: attempt invoke virtual method 'void android.support.design.widget.floatingactionbutton.setonclicklistener(android.view.view$onclicklistener)' on null object reference @ com.example.oscar.app.consulta.oncreate(consulta.java:31) @ android.app.activity.performcreate(activity.java:6664) @ android.app.instrumentation.callactivityoncreate(instrumentation.java:1118) @ android.app.activitythread.performlaunchactivity(activitythread.java:2599) @ android.app.activitythread.handlelaunchactivity(activitythread.java:2707) @ android.app.activitythread.-wrap12(activitythread.java) @ android.app.activitythread$h.handlemessage(activitythread.java:1460) @ android.os.handler.dispatchmessage(handler.java:102) @ android.os.looper.loop(looper.java:154) @ android.app.activitythread.main(activitythread.java:6077) @ java.lang.reflect.method.invoke(native method) @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:865) @ com.android.internal.os.zygoteinit.main(zygoteinit.java:755)

the problem seems following 

textview lab=(textview)findviewbyid(r.id.lab_con);

it seems trying find view not yet drawn on screen. try moving line after activity layout has been drawn this:

super.oncreate(savedinstancestate); setcontentview(r.layout.activity_consulta); toolbar toolbar = (toolbar) findviewbyid(r.id.toolbar); setsupportactionbar(toolbar); textview lab=(textview)findviewbyid(r.id.lab_con);

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