Develop Reference

Running Augmented reality apps on Linux using emulator

In continuation with this question. I am asking this question.
I installed Android Studio. I installed Unity 3D. I followed tutorials of Java-Android Studio and Unity. Nothing worked well because of the reason that they need the latest version of ARCore and neither my mobile nor emulator is compatible with it. I am exhausted searching for alternatives.
I didn't find any tutorial or guidance related to developing Augmented Reality Android apps. Please suggest me a reference that works on Ubuntu system without the need of the physical mobile, but with an emulator, if possible.
Note: Please provide a reference that is relatively easy to test small app initially so that I can proceed forward. I am saying this because of the reason that I am working from almost 3 months but didn't run a small AR app either in the emulator or in my mobile (Redmi Note - 4).

You should check 8thWall. It runs on almost all phones and it has SLAM as well. You can not use it with emulator but it has an application called XR Remote in which you can test your code without building for Android or iOS. Minimum requirement for Android is Android Kitkat (4.4) or higher and for iOS Minimum iOS 7.0 or later is required.
As the owner of the question stated 8thWall can not be used with Linux. As an alternative [ARToolKit] can be used. It is an open source AR framework. For more details you can refer here and here

Tango app for all android devices

I am exploring tango sdk and find some things that i am not able to understand
there is an app called
istaging :- https://play.google.com/store/apps/details?id=com.iStaging.furniture
and there is another app
istaging for tango:- https://play.google.com/store/apps/details?id=com.istaging.furniture.tango
The simple app works for all normal android devices and app which says for tango shows "app is not compatible with your device
now my question is
is there any possibility that can develop app with tango sdk and works for normal android devices?
if yes please guide me how to do that.

Tango SDK only works on Tango-enabled devices, which at the time of writing, are the Yellowstone Devkit and the Phab Pro 2.
If you want to create an app that works on both Android and Tango, first use PackageManager to check if com.google.tango is installed on the device, so you can flag whether the phone is Tango-enabled or not. Learn how to do that here
Then build an AR experience using any AR SDK or OpenCV as to service the general Android market, and then a seperate, specific Tango experience for the ever-growing Tango phone market.
Hope you found my answer useful.

What files needs to be customized during the building process when i'm targeting a specific device / platform in Android?

I can't find a clear list of what files needs developer's attention when i'm building a new Android image.
All the guides that i have found until now are way too generic or really old.
I'm supposing that i'm not interested on customize the platform, i just want a vanilla flavour but for my device only.

The answer is a bit complicated. You probably cannot build a vanilla Android for your device, unless your device is one of the google developer phones. Here is a list of the devices you can build Android for. The reason being that the manufactures usually does not publish all the parts needed to actually build Android for their devices.
But do have a look at the cyanogenmod project, and see if they support your device. They are kind of trying to make a "vanilla" android source for the devices which the manufactures themselves does not support. And they are doing quite a nice job, in my opinion. I have a custom build of Android 4.0 for my Galaxy SII running for months now, and it is working perfectly fine.
If you update your questions with the devices your are using, I can probably provide specifics on how you can build cyanogenmod for your specific device.

What are you trying to do ?
Declare some images or layout specific to only one device ?
You can't do it with a selector on a folder (-large, -fr, ...), but with some code. Check this out : http://developer.android.com/reference/android/os/Build.html#MODEL,

Testing applications on tablets

I am beginner android developer. I am trying to create a simple game using android-ndk and OpenGL-ES, but the emulator unfortunatelly doesn't support OpenGL. What is more it is a bit slow. So, I am planing buying a tablet with android. Maybe Asus Transformer or Acer Iconia. But I am afraid, will I be able to test my applications on these devices? Aren't there any limitations about that? I read some information on the topic and I suppose that I can install apps signed with the debug key...

Yes, you will be able to test the applications on any android tablet that has an equal to or higher version of android to your app. For how to do so look here: http://developer.android.com/guide/developing/device.html.

Do I need the "Android unlocked dev phone" to test my android projects?

I bought an Android phone to use Flash. But to my surprise, Flash does not run on Android devices with arm v6. But I do want to make something useful and develop for it. Does it need to be "unlocked" for this purpose?

Not at all, you can develop Android applications on any Android device. Just make sure that if you want to make use of Google APIs that it's a device that supports those APIs. Also, you'll need to enable development under Settings --> Development (I believe, the location actually varies depending on the version).

Nope, just download the SDK and go. All current phones (that I know of) allow you to do debugging on-device.

If you are developing using the Android SDK or NDK, any phone with Android Market is required to be able to be used as a developer device. If you are trying to develop IN Flash, then you will need a phone capable of Flash (Motorola Droid, any Snapdragon or better processor device) but on Android I don't believe there is a way to package a Flash app onto the device, and the Flash app is always run in the browser.