android - can't modify layout defined in layout.xml at runtime (nullPointerException) -

i can't add sub-layout main layout of activity @ runtime. more precisely null pointer exception when call setcontentview(layout) or layout.add(mysublayout), layout retrieved findviewbyid(r.id.idlay). below here there xml code.

<scrollview xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:tools="http://schemas.android.com/tools"     android:id="@+id/idlay"     android:layout_width="fill_parent"     android:layout_height="fill_parent"     android:fillviewport="true"     tools:context=".trainingacty" > 

seems not possible modify layout created statically. see answers on stack overflow seems possible doing want, , i've never read in documentation of android nothing impossibility of it.

it possible modify layout @ runtime regardless of how created. here's example of how it. assume in example layout posted in file main.xml.

@override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.main);      viewgroup main = (viewgroup) findviewbyid(r.id.idlay);     textview text = new textview(this);     text.settext("this test!");     main.addview(text); } 

this, of course, won't modify resource file, when inflate next time, you'll have run through steps again.