Develop Reference

Does `wrap_content` works the same way as Density Pixels?

I have read Android guidelines regarding different screen sizes, but still I have some considerations.
Client has given me an image from PSD file which has certain resolution that fits
1080 X 1920. I just use wrap_content, and it perfectly fits the part
of screen.
I am not using DP to define its width-height, If i was using DP it would have
adjusted image according to screen sizes.
My questions are,
Does wrap_content works the same way as Density Pixels?
Is it also responsive, and changes the image width-height according
to different screens?
If not, then Is it necessary to use DP to support different screen
sizes ?
Thanks

The setting wrap_content tells your view to size itself to the dimensions required by its content. In the case of your test, your image is 1080x1920 and your device's screen resolution is likely 1080x1920 as well, hence the perfect fit. Since you set the width and height to wrap_content, Android is simply trying to use as much screen space as it needs to correctly display the amount of content it was supplied. In this case, since the available screen space matches the size of the content, it just fits perfectly.
But what if the device screen isn't 1080x1920? In that case, Android will only use as much space as it can, but still attempt to fit the image inside the bounds of the available screen space. In other words, the system will appropriately scale the image down to get it in the container you have provided for it. But this can lead to awkward fits if the aspect ratio isn't the same as the image. For instance, see this screenshot below:
This image is 1920x1080, but notice that it doesn't quite fit. That's because this nexus 7 screen is 1824x1200 when viewed in landscape. Additionally, the toolbar at the top of the screen is eating up available screenspace, making my viewable area even smaller and more awkwardly shaped. So while the system would love this image to extend all the way to the left and right borders, it can't, because then that would mean the height would be bigger than the viewable space. Since I used wrap_content to display this image, the system is using as much vertical space as it can, and the result is that the image doesn't quite fit the horizontal space.
So to more directly address your questions, yes wrap_content is a relative size setting that will make it easier to get a consistent look across multiple screen sizes, similar to using dp. But realize that there are hundreds, if not thousands of available Android devices on the market, and they all have varying screen sizes and densities. So your drawables may not always appear the way you want them on every device.
The way to overcome this is to supply multiple versions of your assets and provide alternate layout files for different screen sizes and densities. Once you do that, all you can do is test, test, and test some more. Use emulators for weird screen densities or devices you don't own, just to make sure you're getting the look you want. In the case of your 1920x1080 image, it looks great on that one device, but how will it fit a large tablet or a tiny handset that is smaller than the resolution of the image? These are situations you must account for in your design.
I suggest you read these resources, as they are hugely helpful in learning how to deal with issues resulting from varying screen sizes and densities:
http://developer.android.com/guide/practices/screens_support.html
http://developer.android.com/training/multiscreen/screensizes.html

Android layouts size and resize

I am doing a lot of work about android layout I still can't create a layout working in every phone. I am not sure about best the way to create a layout so correct me if I am wrong . There are three things to keep in mind :
Screen px (resolution, for example 1080x1920 px)
Screen dimension "inches"
Screen density dp or also called dpi ( dp is a virtual resolution, it's correct?)
To draw a layout working in every phone (my app will works for phones) do I have to create a directory "layout-kindofdensitydpi for every screen density (layout-ldpi,layout-mdpi,layout-hdpi,layout-xhdpi,layout-xxhdpi,layout-xxxhdpi) and draw "manually" or do I have to do something else?
I did a test, I created these 6 directory and drew manually for every resolution. It requires a lot of time, also device with a resolution of 768x1280 my app doesn't respect what I drew, for example spaces aren't respected, the collocation of elements doesn't result correct and frame layout with ImageView inside isn't scaled.
What I have to do? In some Android books isn't mentioned that elements could not resize and usually them explain how to put some text or image without analyse resize in every device.
Thanks in advice

First you should find the appropriate layout type for your UI (RelativeLayout or LinearLayout). Sometimes using a good layout(or nested layouts) can make the UI look good on every screen. I prefer LinearLayout cuz I can simply set layout_weight for components.
Then set different sizes in dimens.xml file for different densities or screen size buckets. Like this:
And you can also use match_parent or wrap_content
Don't forget to set the screen orientation of your activity if it doesn't need to rotate. Having one orientation makes it much easier to design.
If you couldn't make a good layout using tips above you should create multiple layouts to fit every screen size or density (Screen size and density are two different things).
You should find the best way to determine your screens according to.
Screen size bucket (small, normal, large, and xlarge) picks a layout that fits the screen (or the closest), density bucket (ldpi, mdpi, hdpi, xhdpi, xxhdpi, and xxxhdpi) picks a layout according to the density ,or the smallest width (I think it's almost the same thing as density).
480dp is the sw of these two devices
You can make layouts for different screen orientations too.
I don't like creating layouts for different screens for some reason. One of them and the most important is that sometimes same screen sizes have different densities and it makes it hard and time consuming. To create a layout and you should also provide a lot of pictures.

Use
android:layout_width="match_parent"
android:layout_height="match_parent"
to the outer layout to get access of the full screen of the device.
Also, if there are no changes in your UI then you don't need to create different layout folders.
Refer http://developer.android.com/training/multiscreen/screensizes.html

You should have a look at
http://developer.android.com/guide/practices/screens_support.html
http://developer.android.com/training/multiscreen/screensizes.html
http://developer.android.com/training/multiscreen/index.html
I would suggest using layout-swXXXdp or layout-large etc instead of layout-KindOfDensitydpi
Create your relative layouts using RelativeLayout and use the weights of LinearLayout. Don't hard code any of the positions in the layout

Size of Android Screens with no status bar and softkeys

What is the applications screen size without the status bar and softkeys(in some phones)?
Like for Example i know:
320X480 trimmed down to 320X455 which is the basesize.
but what about others , i have done many calculations and a lot of searches online to figure out a defined size for other screen but i seems can't, Also While applying the formula *.75 ldpi, *1.5 hdpi, *2.25 xhdpi to get other screen, it doesn't add up.
Like 320X480 is mdpi to get the hdpi do *1.5 and you will get 480X720 which is not the situation for devices out their ! and using this method my application images where stretched, this method is according to the Google documentation, i'm confused as hell.
I have tried to et sizes using the emulator also it was very different! for height.
So if the problem is with height only, i'm thinking creating background as patterns and then work only on the width of the screen size and re-size every other elements to screen width only like 240px, 320px, 480px, 720px and also consider the size of them to fit minimum height.
I believe it's not possible to define a height for android which will go like generic because of the variety of android devices.
So what do you think about this approach to use background as pattern and forget about every device on earth height ?

you can use tile pattern, create a small texture and then make it tileable drawable in xml, so it will be tiled across screen, or the second might be using 9-patch images, in that way you can select which area of the image scale and which area to not scale, so they will be scaled according to that way.

Why is my layout not Density Independent?

My layout as shown below looks very different depending on what screen size it is projected on to. I'm aware I can improve this somewhat using different layouts for each screen size but considering I have followed the best practises described in the android multiple screen support documentation (using dps, no absolute layouts etc) I wasn't expecting the results to look this bad so I fear there is a further underlying problem.
Code:
http://pastebin.com/D96ue9sc

Your layout is fine and completely as I would expect it. You shouldn't mix up density independent pixels with fully dynamically layouts.
DP just means that the value is calculated according the density types. The density itself has nothing to do with screen resolutions. 60dp are 60px on a mdpi device, it doesn't matter if the screen is full HD or just 480x360. But the result is, of course, very different because the calculated 60px are nothing on a HD screen but a lot on a small one.
You have not other possibility but to provide different layouts according to the screen size/resolution.

What resolution should my Android splash screens be?

I'm creating a splash screen that will display while my Android application loads. I'd like to create it at the correct size so Android won't auto-scale it up or down to fit the screen. (It's a bitmap image, a photograph of an oil painting, so I can't just turn it into a nine-patch.)
But there are at least three important screen sizes I care about: 320x480, 480x854 (Droid), and 480x800 (Nexus One).
I've read the documentation on supporting multiple screen sizes, but I still don't see how I'm supposed to configure different splash screens for Droid/Nexus one (they're both "hdpi" resources as far as Android is concerned), and I don't know exactly how large my splash screen should be in any case. (How tall is the OS title bar/menu in Droid? N1?)
What size should I make these images, and how do I tell Android to use the correct size on a given screen?

You don't need to worry about the absolute screen size or status bars or anything — that's why we have nine-patch images.
What I did was have an image that looked good for each resolution — essentially a logo on a transparent background, with some text at the bottom.
Then I chopped off quite a lot of space at the top and side edges, made a nine-patch border round the image, with a single pixel near the left, right and top edges. This allows the image to expand evenly at the sides and top to fill the screen.
Edit, in response to Dan's comment below:
Yes, there is a way to determine which graphics should be used for which explicit screen sizes, but it's deprecated.
Just as there are drawable-hdpi and -ldpi resource qualifiers, it's also possible to use drawable-HHHxWWW — the larger pixel dimension coming first.
e.g. drawable-800x480 and drawable-854x480

Okay, firstly: you can find the device model via android.os.Build and use that to determine which image to show.
Secondly, I personally wouldn't bother. Layouts should be done in dip since every android screen is 320x480 dip I believe, and android maintains aspect ratio among devices very well through this in my experience. A 480x800 splash set to fill parent has been pretty reliable on both N1 and the droid as far as I have encountered.

Another solution that I implemented is to put an ImageView that fills the screen (width and height both "MATCH_PARENT") with scale type "centerCrop". This way, the image is not stretched but cropped along the edges. Try not to put important content (logos and stuff like that) close to the edges. If it is a photograph, I hope that the edges are "expendable" and can be cropped out.