Setting android:windowBackground to @null makes scrolling to smear?

Question

i'm using the sherlock actionbar library in order to support many devices . i have a viewPager which has 3 fragments :

one with a listView , each item has a textView and an imageView
the second has a gridView , each item has a textView and an imageView
the third just has a textView for now.

as i've heard in google IO videos (and since Lint tells me) , it's recommended to have the next style being used for all of the activities:

<resources xmlns:android="http://schemas.android.com/apk/res/android">

  <style name="AppTheme" parent="@style/Theme.Sherlock">
    <item name="android:windowBackground">@null</item>
  </style>

</resources>

this has worked for me on many devices .

however , on the emulator , using version 2.3.3 , and on galaxy nexus , when i scroll (either the viewPager or any of the adapterViews) , everything just smears , so i get a lot of white pixels as if nothing was refreshed.

i've even tried to set android:cacheColorHint="#00000000" for all of my adapterViews , but it still occurs.

what is going on? how can i fix this thing ? i like adding the above since it removes the ugly gradient background of galaxy S3 that appears for every app.

it wrote an error :"Error: Color types not allowed (at 'android:windowBackground' with value '#ff000000' ..." ,so i've tricked the compiler and gave it a color from the res folder , and then it worked , but i don't remember what was the reason for the suggestion , so i'm not sure if that helps . all i remember is that romain guy was the one lecturing about it. anyway , why don't you put your answer instead of putting a comment? — android developer, Aug 28 '12 at 06:00
Hmm you know better what you did there to get a solid background, so IMO you should write what you did as answer :) — zapl, Aug 28 '12 at 14:10
i'm not sure it helps , since i don't remember what does this optimization do . i think it's a better way to remove/set the background of the activity than setting it for the layout itself . — android developer, Aug 28 '12 at 14:59

score 11 · Accepted Answer · answered Dec 11 '12 at 01:31

11

You should only set the background to nul if you cover it with something else. Either: - Set the background to null in the theme and add a new background in your layout or - Set the background in your theme to the color/image you want.

answered Dec 11 '12 at 01:31

Romain Guy

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1

btw , why does setting the background on both the listView and the window to null causes the weird smear to occur? – android developer Dec 11 '12 at 06:56
2

Because you don't have a background so Android does not clear the window. – Romain Guy Dec 11 '12 at 18:04
when you say "doesn't clear the window" , does it have anything to do with glClear ? i thought there is a default color of the window to be used. – android developer Dec 11 '12 at 19:27
There is a default color but when you set the background to null you tell Android to not use it and not draw anything. – Romain Guy Dec 11 '12 at 20:34
how come this affects only some of the devices , and only for adapterView (at least that's what i saw) ? – android developer Dec 11 '12 at 23:04

Setting android:windowBackground to @null makes scrolling to smear?

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