findViewById(R.id.screen) returns null

Question

I am trying to change background color of my app when user drags the seekbar.

I have refereed following link : Set Background color programmatically

I have following code in OnSeekBarChangeListener() :

@Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
    View someView = findViewById(R.id.screen);
    View root = someView.getRootView();
    root.setBackgroundColor(Color.argb(255, r[progress], g[progress], b[progress]));
}

It results in following crash :

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.getRootView()' on a null object reference

Mainactivity class :

  protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        setRandomcolors();
        setbuttonclicklistener();
        seebar();
    }

OnSeekBarChangeListener() is called from seebar()

have you set setContentView(your layout)? can you please share more of your code? — KDeogharkar, May 21 '16 at 11:29
add ID to your layout (activity_main). `android:id="@+id/screen"` — Bogdan Kuštan, May 21 '16 at 11:32
did you try someView=activity.getCurrentFocus().getRootView() ? — Malith Lakshan, May 21 '16 at 11:32

score 2 · Answer 1 · answered May 21 '16 at 11:40

2

You are getting someView as null. So its giving null pointer exception.

Try changing,

 View someView = findViewById(R.id.screen);

to

 View someView = (View)findViewById(R.id.screen);

Can you post your full xml code.

answered May 21 '16 at 11:40

Ashwini

245
1
7

2

I think it really does not matter if he converts the null value to 'View'? – whymatter May 21 '16 at 11:53
could use: if (someView != null), but you might need this: View daddy = (View) (findViewById(R.id.screen)).getParent(); – Flummox - don't be evil SE May 25 '16 at 15:40

findViewById(R.id.screen) returns null

1 Answers1