Is there a performance impact, especially with regard to battery performance, if we switch from the default black theme of android to white or another colour?
If the screen is LCD white light consumes less power than the black.
What Chimmy said, plus for AMOLED displays black uses less power as far as I know. The Nexus One is AMOLED and Samsung Galaxy S is Super AMOLED.
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I have a ScrollView with some children inside.
For API 23, the ScrollView has a white background. But for API 22 and below, the background is gray. I didn't set background in xml or code. All remaining default. Activity and fragment also have default background in layout xml. Activity theme is Theme.Holo.Light.NoActionBar by default, and Theme.Material.Light.NoActionBar for v21.
I saw this on:
samsung note 5 with 6.0.0: white
android emulator Nexus 6P with 6.0.0: white
samsung s6 with 5.1.1: gray
android emulator Nexus 6P with 5.1.1: gray
Xiaomi 4 LTE with 4.4.4: gray
android emulator Nexus 6P with 4.4.4: gray
based on the above test, I guess the background related to API levels.
If I set background to white in xml, for API 22 and below, I can see white background.
Any ideas?
If you haven't provided an explicit color, it might take the color from the default theme of the device. It doesn't depend on the API level, but the device theme.
Therefore, its also possible that you might see different colors for the same API level on two different devices.
Hence, if you want to be consistent across all devices, its always recommended to set the color you want explicitly.
Try this in your styles for the same background in different android API:
<item name="android:windowBackground">#color/background</item>
As the title question, is it really save energy?
as we know the white color is come from maximum light in RGB which mean maximum power to draw it in display.
according to this article: http://www.scientificamerican.com/article/fact-or-fiction-black-is/
New advances in LCD technologies could eventually validate the belief that black is better. Newer types of LCD include a dynamic dimming capability that changes the strength of the backlight based on the image being displayed. Heap also points out that many of the new monitor technologies such as LCDs backlit with light-emitting diodes (LED), plasma screens and organic LED screens do not have a constant backlight "so we will see larger savings with Blackle as these new monitors replace the CCFL LCDs," he says.
For those who've graduated to thinner LCD models, black screens are actually sucking up more energy then their white counterparts.
and from wikipedia:
The amount of power the display consumes varies significantly depending on the colour and brightness shown. As an example, one commercial QVGA OLED display consumes 0.3 watts while showing white text on a black background, but more than 0.7 watts showing black text on a white background
...
Because the black pixels actually turn off, AMOLED also has contrast ratios that are significantly better than LCD
so it really depends how a screen treat it's constant back light.. seems like OLED and therefor AMOLED perform better then LCD screens on that matter
Apparently it is true. As I understand it, modern amoled screens work by only lighting up the pixels that are needed. This is in contrast to LCD screens where there is a constant backlight that is always on. In LCD screens they achieve a black pixel not by turning off the backlight but rather by filtering out any light from passing through a given pixel. Therefore the energy used by the backlight is not any less, the light output just doesn't make it out of the panel and to your vision.
AMOLED otoh actually lights only lit pixels. Blacks are represented by not turning on the pixel in the first place. This does amount to an energy savings commensurate with the amount of black on the screen. More black = more pixels NOT turned on = more energy NOT used = energy "saved"
Here is a link to a basic test done by Android Authority. However basic the test is, the results are pretty clear..
I developed my app on a Samsung GT-P7510 (10.1" WXGA 1280x800 pixels). When I download to the Nexus 7 (7" 1280x800 pixels) the buttons that I use appear to be about the same physical size. The Nexus buttons are about 95% of the Samsung buttons. The rest of the screen seems to work OK- the text is in the right location and is proportionately smaller because that is defined in terms of screen height.
All my button sizes are defined using "dp" settings in the XML layout files. I would have expected that with the same pixel ratio the buttons would scale. I am obviously misunderstanding this. What setting would I use to get the buttons to scale?
Why do you think Android should scale your app without anything that you tell it to do?
"dp" simply makes things look the same across devices with different densities (higher density makes use of more pixels) . It won't make things larger or smaller, and it's a good thing since you don't want text to be either huge or too small to be able to read.
For text, BTW, it's usually better to use "sp" so that the user might be able to change its size (because people might have eyes problems to read small letters).
If you wish to scale things, you can either create your own mechanism (like this one) or use openGL .
I'm developing an application for Android, and the colors of drawables changes when I'm testing the app on Samsung Galaxy S2, and when I test the application on Samsung Galaxy Europe or on emulator, appears the real colors of the drawable. For exemple, the gradient white and black, is different on Samsung S2.
Why this happening?? Can I do something on application to show the real colors on Samsung S2?
By default when we use transparent images in our app mostly the transparent part will show its parent.
For example if we use transparent images for menus in android.
then by default the theme of the device/background will be the parent view for this image.
According to me better to change the image and try.
I know that the screen resolution is 1280×800px but Honeycomb's bottum menu bar makes this a tad smaller, but how much smaller?
Has google published the height of the menubar? (the one that can't be taken away as it has the home/back etc buttons)
I want to know this because when I draw a fullscreen background for the Tab I want to know the exact size as to get a pixel perfect result.
The height of the menu bar on Honeycomb is 48 pixels, for devices with 1280x800 pixels at least.
Yes its 48 on Samsung Galaxy P7500 10.1
Use http://supportdetails.com/ to find out the size. Remember. You can rotate a tablet!