CODEWITHSUNDEEP
androidanimation
newbee
newbee

Reputation: 409

flashing background

I have a LinearLayout with a few Buttons and TextViews. I want my background to flash at timed intervals, say from red to white to red and so on. Right now, I am trying this code, but it gives me a null pointer exception. 

LinearLayout ll = (LinearLayout) findViewById(R.layout.activity_main);
Animation anim = new AlphaAnimation(0.0f, 1.0f);
anim.setDuration(50); 
anim.setStartOffset(20);
anim.setRepeatMode(Animation.REVERSE);
anim.setRepeatCount(Animation.INFINITE);
ll.startAnimation(anim); // shows null pointer exception at this line

Please help me where am I going wrong?

Upvotes: 8

Views: 13373

Answers (2)

Vladimir Mironov
Vladimir Mironov

Reputation: 30874

You have specified the wrong View id here findViewById(R.layout.activity_main). It should be something like:

findViewById(R.id.your_view_id);

Also, make sure to call setContentView(R.layout.activity_main) right after super.onCreate

EDIT:

Here is the code that allows you to change only the background color with any colors you want. It looks like AnimationDrawable.start() doesn't work if called from Activity.onCreate, so we have to use Handler.postDelayed here.

final LinearLayout layout = (LinearLayout) findViewById(R.id.layout);
final AnimationDrawable drawable = new AnimationDrawable();
final Handler handler = new Handler();

drawable.addFrame(new ColorDrawable(Color.RED), 400);
drawable.addFrame(new ColorDrawable(Color.GREEN), 400);
drawable.setOneShot(false);

layout.setBackgroundDrawable(drawable);
handler.postDelayed(new Runnable() {
    @Override
    public void run() {
        drawable.start();
    }
}, 100);

Upvotes: 24

Chirag Patel
Chirag Patel

Reputation: 11508

Try this

LinearLayout ll = (LinearLayout) findViewById(R.id.activity_main);
Animation anim = new AlphaAnimation(0.0f, 1.0f);
anim.setDuration(50); 
anim.setStartOffset(20);
anim.setRepeatMode(Animation.REVERSE);
anim.setRepeatCount(Animation.INFINITE);
ll.startAnimation(anim);

and If activity_main is your XML file name then 

setContentView(R.layout.activity_main);

and use your layout id here

LinearLayout ll = (LinearLayout) findViewById(R.id.linear_layout_id);

Upvotes: 6

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