android - onCreate Null Pointer Exception -

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• nullpointerexception accessing views in oncreate() 11 answers

i don't understand why code not running:

protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_matchpage);      seekbar sb1 = (seekbar) findviewbyid(r.id.seek1);             sb1.setenabled(false);      if (savedinstancestate == null) {         getsupportfragmentmanager().begintransaction()                 .add(r.id.container, new placeholderfragment()).commit();     } } 

sb1 null. why?

you using fragment. should have in code class called placeholderfragment, has oncreateview method.

in project have 2 xml layout, 1 named activity_matchpage , other fragment, fragment_main. need modify latter , keep first this:

<framelayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/container" android:layout_width="match_parent" android:layout_height="match_parent" tools:context="youor.packaque.mainactivity" tools:ignore="mergerootframe" /> 

and in fragment_main, declare views.

<relativelayout xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:tools="http://schemas.android.com/tools"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:paddingbottom="@dimen/activity_vertical_margin"     android:paddingleft="@dimen/activity_horizontal_margin"     android:paddingright="@dimen/activity_horizontal_margin"     android:paddingtop="@dimen/activity_vertical_margin"     tools:context="com.tformacion.finale.mainactivity$placeholderfragment" >          <!-- views here -->  </relativelayout> 

then, in java code, in placeholderfragment, inside of oncreateview:

    @override     public view oncreateview(layoutinflater inflater, viewgroup container,             bundle savedinstancestate) {         view rootview = inflater.inflate(r.layout.fragment_main, container, false);          seekbar = (seekbar) rootview.findviewbyid(r.id.yourseekbarid);      } 

if want rid of fragment create xml in activity_matchpage , not add fragment, so, remove this:

if (savedinstancestate == null) {     getsupportfragmentmanager().begintransaction()             .add(r.id.container, new placeholderfragment()).commit(); }