onCreate Null Pointer Exception

Question

I don't understand why this code does 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 will be null. Why?

Answer 1

I will try to answer one thing from my experience that the error is coming in SeekBar sb1 = (SeekBar) findViewById(R.id.seek1); but what i have noticed android compiles code from bottom so it might happen that the reason is above or somewhere else so what i will suggest replace the code in this manner :-

1. protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_matchpage);
   }
   

2. then if it executes then just add SeekBar sb1 = (SeekBar) findViewById(R.id.seek1); below setContentview

its bit big but since you didnt provided the xml and we cant figure out if its package issue or something else so i tried to go really primitive and fundamental...

hope it helps.

Answer 2

You likely are using a Fragment. You should have in your code a class called PlaceHolderFragment, that has an onCreateView method.

In that project you have two xml layout, one named activity_matchpage and other for the fragment, fragment_main. You need to modify the latter and keep the first like 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, you declare your 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" >

        <!-- Your Views here -->

</RelativeLayout>

Then, in your 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 you want to get rid of the fragment you simply create your XML in activity_matchpage and do not add the fragment, so, remove this:

if (savedInstanceState == null) {
    getSupportFragmentManager().beginTransaction()
            .add(R.id.container, new PlaceholderFragment()).commit();
}