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?
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);
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);
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