Develop Reference

how to know which phone support which layout(hdpi , mdpi and xhpi)?

I'm a little confused about how to determine which phones support what layout types. I've done some research but haven't found a satisfying answer.
For example, I've found the below guide:
xlarge screens are at least 960dp x 720dp
large screens are at least 640dp x 480dp
normal screens are at least 470dp x 320dp
small screens are at least 426dp x 320dp
However, I still have some concerns:
Samsung grand (480*800) and HTC wild fire S (320*480) both support MDPI. These screens have very different resolutions, yet have the same layout type?
Galaxy note 2 (1280*720) support HDPI. If HD (720p) is only HDPI, when what device/resolution supports XHDPI?
I've already asked a related question here: How to set layout on 7" two different tablet?.
My most important question, however, is this: How do I know which devices or screen resolutions support each layout type?

Android treats mdpi (160 pixels/inch) as the base density. So for mdpi devices, 1 dp = 1 pixel. At higher densities, there are more pixels per inch (240 for hdpi, 320 for xhdpi).
AutoMatic Scaling by Android itself:
Android attempts to make graphic images occupy the same physical dimensions on the screen regardless of the device pixel density. So if all it finds is an mdpi resource, and the device is hdpi, it will scale the graphic by 240/160 = 150%, and it will double the size of the graphic for xhdpi.
Using different versions of graphics :
If you don't want this automatic scaling (which can make graphics look poor), you can simply supply your own version of graphic resources for use at higher densities. These graphics should be of the same size that Android would scale an mdpi resource.
Note : the pixels/inch that was stored in the image file has nothing to do with this. It's all based on where you put the graphics files in the resources directory for your project. Any graphics placed in res/drawable are assumed to be properly sized for mdpi displays, as are graphics placed in res/drawable-mdpi. Image files that it finds in res/drawable-hdpi are assumed to be properly sized for hdpi displays, etc. When your program runs on a particular device, Android will first look for a graphic that matches the display density of that device. If it does not find one but instead finds one for a different density, it will use that and automatically scale the image based on the above rules.
As the ldpi, mdpi and hdpi refer to screen density, which means how much pixels can fit into a single inch.
the ratio in pixels between them is:
ldpi = 1:0.75
mdpi = 1:1
hdpi = 1:1.5
xhdpi = 1:2
xxhdpi = 1:3
so lets take an image with about the size of 100X100:
for mdpi it should be 100X100
for ldpi it should be 75X75
for hdpi it should be 150X150
for xhdpi it should be 200X200
for xxhdpi it should be 300X300
this way, for screens with the same size but different DPI, all the images seem the same size on screen.

look into these details: android manages all this by itself, you just have to provide layouts and images in relative folders
res/layout/my_layout.xml // layout for normal screen size ("default")
res/layout-small/my_layout.xml // layout for small screen size
res/layout-large/my_layout.xml // layout for large screen size
res/layout-xlarge/my_layout.xml // layout for extra large screen size
res/layout-xlarge-land/my_layout.xml // layout for extra large in landscape orientation
res/drawable-mdpi/my_icon.png // bitmap for medium density
res/drawable-hdpi/my_icon.png // bitmap for high density
res/drawable-xhdpi/my_icon.png // bitmap for extra high density

size of app's background for various Android devices

I am designing a background for my app for all Android devices.
I was thinking what would be the size of the image in pixels?
From the developer site I found the following equation
px = dp * (dpi / 160)
Then, px depends on two variables.
First, dp, and we have
xlarge screens are at least 960dp x 720dp
large screens are at least 640dp x 480dp
normal screens are at least 470dp x 320dp
small screens are at least 426dp x 320dp
Second, dpi and we have
low-density (ldpi) screens (~120dpi).
medium-density (mdpi) screens (~160dpi).
high-density (hdpi) screens (~240dpi).
extra high-density (xhdpi) screens (~320dpi).
So where should I put my drawables in the Screen characteristic? I mean should I use "size" or "Density". If I classify my images using the "size" "dp", what is the dpi for these images?
and if I classify my images using the "density" "dpi", what is the dp for these images?
I am confused on how to finally size my images. Also, Maybe you can have a medium density screen with a large screen size, right?

There are many many different resolutions out there. For instance there could be 4 different devices which are:
640 px x 480 px
The difference is, some of these devices are mdpi, some are hdpi, xhdpi etc. meaning they could be described as "large", "medium" or "xlarge" screen types.
So, for an mdpi device which is 640x480dp the background would be 640x480px however, a device which is 640x480dp and hdpi would need a background which is 960x720px, you'll notice they're the same size "bucket" but have different densities and therefore different resolutions.
So, if you just want your background to fit as well as can be expected you'll need:
large-xhdpi
large-tvdpi
large-hdpi
large-mdpi
large-ldpi
(then the same for normal)
normal-xhdpi
normal-tvdpi
etc etc etc.
You're best bet however is to use an image which can stretch, a shape, tile or can be converted to a 9-patch because it would be a pain in the rump to make every background available for every device. If you were going to do it I would look up a resource descrivbing every screen dimension on the market currently and setting it via programmatic methods.

android how to support multiple screen

Thais is what I have done. I try to support this screen sizes:
xlarge screens 640dp x 960dp
large screens 480dp x 800dp
normal screens 320dp x 400dp
small screens 240dp x 400dp
So I create etc. background images with that sizes (640dp x 960dp, 480dp x 800dp, 320dp x 400dp and 240 x 400). I put images in folders drawabale-xhdpi, drawabale-hdpi, drawabale-mdpi and drawabale-ldpi.
When I have xlarge screen with hdpi density (it use images from hdpi folder), graphic is bad (images are not large enough). So how to use that xlarge image when I have hdpi density. Do I have to create more images and put them in some places? This is a game, I draw all in canvas, don't use layouts for drawing images.
Thanks.

You can add new drawables in a drawable-xlarge-hdpi folder

use this path to save your image
res/drawable-xhdpi/my_icon.png // bitmap for extra high density
Check this Supporting Multiple Screens for more clarifications of multiple screen support.

Take a look at this link - Providing Resources
You can have an image in drawable-xlarge-hdpi folder

always use relative layouts to support multiple screens. see here Android layouts for same density different diagonal length

Support same-resolution but different-DPI screens

I need my app to support 480x800 normal hdpi and 480x800 large mdpi screens. The UI for them is the same. The matter is using dp in this case is a wrong way because on hdpi device everything becomes larger. But I need just scalable UI.
Is it possible I provide that by using single version of layout files?

use 2 set of images and put in the 1.x mdpi and other in 1.5x hdpi
here 1 and 1.5 is size ratio
only one layout xml file is enough.
EDIT:
//while design keep in mind with 1x that is mdpi
//for example if you set 5dp for you mdpi resolution
it will automatically change for hdpi as
5*240/160=7.5 px //for hdpi
5*320/160=10 px //for xhdpi

Android screen sizes in Pixels for ldpi, mdpi, hpdi?

I've read 10 articles yet still cant find any relation between ldpi, mdpi, hdpi and the actual dimensions in pixels!? Can anybody give a straightforward answer please(if there is one!)
I'm basically trying to put together a splash screen that needs to work on multiple devices without stretching - but i'm struggling as everything I try is either squashed or stretched!?
Cheers
Paul

The ldpi, mdpi and hdpi refer to screen density, which means how much pixels can fit into a single inch.
the ratio in pixels between them is:
ldpi = 1:0.75
mdpi = 1:1
hdpi = 1:1.5
xhdpi = 1:2
xxhdpi = 1:3
xxxhdpi = 1:4
so lets take an image with about the size of 100X100:
for mdpi it should be 100X100
for ldpi it should be 75X75
for hdpi it should be 150X150
for xhdpi it should be 200X200
for xxhdpi it should be 300X300
for xxxhdpi it should be 400X400
this way, for screens with the same size but different DPI, all the images seem the same size on screen.
Also you have multiple screen size types small, normal, large, xlarge and each one of them can be ldpi, mdpi, hdpi, xhdpi, xxhdpi (Nexus 10) or xxxhdpi.
You can try to create a splash screen image that fit to each and every screen type
which gives you 4*5 = 20 different images (it seems to much for me).
For now only the Nexus 10 is at the xxhdpi category.

Install ImageMagick and use this shell script to generate your splash and icon files for multiple devices - iOS, Android, Bada and Windows Phone. You can use cygwin/gitbash if you are on Windows
I just did and I'm pretty happy with it :-)
The screen sizes are inside the script and are -
480x800 - screen-hdpi-portrait.png
320x200 - screen-ldpi-landscape.png
720x1280 - screen-xhdpi-portrait.png
320x480 - screen-mdpi-portrait.png
480x320 - screen-mdpi-landscape.png
200x320 - screen-ldpi-portrait.png
800x480 - screen-hdpi-landscape.png

The definitions are:
xlarge screens are at least 960dp x 720dp. large screens are at
least 640dp x 480dp. normal screens are at least 470dp x 320dp.
small screens are at least 426dp x 320dp. (Android does not currently
support screens smaller than this.)
Also, check out this blogpost from Dianne Hackborne:
http://android-developers.blogspot.com/2011/07/new-tools-for-managing-screen-sizes.html
Probably the easiest thing is to use an image view and set the scaletype to CENTER_CROP.
(Scale the image uniformly (maintain the image's aspect ratio) so that both dimensions (width and height) of the image will be equal to or larger than the corresponding dimension of the view).
Make sure that you use the src tag rather than setting the background.
<ImageView
android:id="#+id/home_video_layout"
android:src="#drawable/splash_image"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:scaleType="centerCrop"
/>
Updated:
Understanding Screen Densities and the “dp”
Resolution is the actual number of pixels available in the display, density is how many pixels appear within a constant area of the display, and size is the amount of physical space available for displaying your interface. These are interrelated: increase the resolution and density together, and size stays about the same. This is why the 320x480 screen on a G1 and 480x800 screen on a Droid are both the same screen size: the 480x800 screen has more pixels, but it is also higher density.
To remove the size/density calculations from the picture, the Android framework works wherever possible in terms of "dp" units, which are corrected for density. In medium-density ("mdpi") screens, which correspond to the original Android phones, physical pixels are identical to dp's; the devices’ dimensions are 320x480 in either scale. A more recent phone might have physical-pixel dimensions of 480x800 but be a high-density device. The conversion factor from hdpi to mdpi in this case is 1.5, so for a developer's purposes, the device is 320x533 in dp's.

I have found this online dip <--> pixels calculator very useful.
https://pixplicity.com/dp-px-converter/

I support previous answers but don't forget the power of Draw9Patch or using NinePatchDrawables

These refer to screen pixel density, not screen dimension. You need to look into screen size specifiers like small, medium, large, and xlarge instead if you really need to change behavior based on screen size in pixels.
The Android docs explain what densities and sizes match these identifiers.

Android devices can have different width-to-height ratios, while your image has a fixed one. If you do not want your image stretched, you will have to fill the blank spaces above and below or left and right.