Develop Reference

Is it possible to recover overwritten files from Android Studio?

For a mistake i've overwritten my two project that has same names from android studio and i've dismissed that action today i've tryed to open the main project and i've found no Java classes in it and just the layout's files.
While in the second project to which i was overwritting there is a huge confusion of files and trying to recover the project version by using history of Android Studio even those files has disappeared.
Is it possible in anyway to recover the whole project?
Ps: all that remain from that project is a generated apk.

I have some solutions that may work.
Candidates are:
Search for $AppData$ folders
Search for registries
(Hardest) you may have to preserve the disk state and carve the files yourself..
Cheers, and hope it helped..!
To use the third method(file carving), you may not cause many file operations occur!!(The system may overwrite the previous data)

Hopefully you used source control such as git or svn and it is a simple matter of reverting to the last commit you made, however that is done in your chosen source control. If you don't use source control, perhaps this will serve as a lesson to do so in the future.
I've not used Android Studio, but as a JetBrains product like IntelliJ, it will have a local history record of changes. But that would only record very recent changes.
If that doesn't work, you may have to find out if your chosen operating system backed up the files in a restore point etc.

If you have turned on the file history, you can use that to go to a previous version of the folder. Can also use system restore to go back to a previous date. Can also use third party softwares such as Recuva to get deleted files back.
Make sure to keep a copy of current state somewhere before trying these out.

Debug on many phones in Android Studio

Is it possible to debug an app on many phones at the same time in Android Studio? By this I mean launching multiple debug instances, each one on a different phone, like in Eclipse.

At the time of posting this question probably the only solution was the one posted by George V.M. Now, after several updates of Android Studio, this can be easily done by creating N copies of the same Debug configuration and launching each of them on a separate phone.

Update
You might want to take a look at Vlad's answer. This one is pointless for newer versions of Android Studio. In case anyone is still curious, this was my really hacky way of solving the problem
In case anyone out there is still looking for a solution to this, here's what I've found.
I'm working on a project that requires wireless communication between 2 instances of the same app running on 2 phones (actually, 2 or more). There were a lot of times where I wished I could debug 2 devices at a time. It wasn't until recently that I figured out how to do it.
It's actually quite simple: Have 2 instances of Android Studio open and you can debug multiple devices at once, (one device on each Android Studio instance) with breakpoints and everything!
Catch 1: You can't open two instances of the same project
I haven't been able to run two instances of Android Studio where both instances have the same project open. It will just redirect you to the already open project.
Solution:
The solution to this is to just make a copy of your project somewhere on your PC and open that project allowing you to have two copies of the same project open.
Catch 2: Changes have to be made on each copy manually.
Now here's a new problem. What if while debugging, you find a mistake in your code and amend it. Now you have to make sure you make that exact same amendment in your second copy of the project so that the second device doesn't have the same error if it hits those lines. This is annoying, having to remember to make a change twice; once in each copy of the project.
Solution:
My solution to this problem was to just make a 'symbolic link' of the project instead of a physical copy.
(A symbolic link is a 'nickname' or a 'reference' to a file. If you make a symbolic link fileB that points to fileA, although they seem like two distinct files to the OS, they in fact point to the exact same physical file. Any changes made on fileA will be reflected in fileB since they point to the same physical file/data on the disk. Instructions on how to create symbolic links are given below)
Now hold on just one second!!! Making a symbolic link of the entire project might not be a very smart idea since you'll have two Android Studios trying to edit the same files. This could lead to problems, especially in the case of build files and IDE files.
So what I did was make a symbolic link of only the source files, or any file which I'd be editing directly and which AS wouldn't normally touch, and make a physical copy of every other file.
The only thing you need to do is remember to hit Ctrl+S after making changes to your code in one AS instance so that the changes will be reflected on the second one. It might still take a couple of seconds for those changes to be reflected in the second instance but you can just click the "Synchronize" button (top left, next to "Open" and "Save") on your second AS which will cause all externally changed files, i.e., the file you just edited in your first instance, to be reloaded from disk.
You still need to be careful though. Every time you make a change in one AS, make sure you save all those changes and that those changes are reflected in the second AS before you try doing any editing in the second AS. Otherwise conflicts could cause you to lose the changes you made in one copy. One way around this is to force yourself to make changes to a file only on one AS and not the other.
Actual Instructions:
Okay that was a lot of talk. Here are the steps you can follow along with tips:
Close Android Studio and make a copy of your project into another folder on your PC
Go to your second copy and delete all your source code files since we're going to make symbolic links of them.
(these are the files I usually make symbolic links of instead of a copy:
all build.gradle files
the entire app/src folder
if you have any other loose source or resource files or othwerwise non IDE files that you might edit, make symbolic links of them as well
Make a symbolic link of all those non IDE files from the first project folder into your second project folder.
to make a symbolic link of a file in Windows, use
mklink path\to\symbolic\link path\to\original\file
to make symbolic link of a folder in Windows, use
mklink /j "path\to\symbolic\link" "path\to\original\folder"
to make a symbolic link of a file or folder in Linux, use
ln -s "path/to/original/file_or_folder" "path/to/link"
Open up Android Studio again. It will probably open the original copy of your project if that was the last project you opened in AS.
Go to File>Open and open up the second project copy on your PC.
You will now have 2 copies of your project running and you will be able to debug your app on 2 devices at the same time! (Remember that breakpoints won't be shared between the two copies)

If you are talking about attaching the debugger to several phones, I'm going to say no.
The port will be blocked with that traffic from one phone.
Unless someone figure out a hacky way to do this, atm It's not possible as far as my knowledge.

Android studio has its VM devices, but it requires installing Intel Accelerator because it's too slow until it show up. alternatively, I recommended "Genymotion" for running multiple instances and different devices. I'm using it and its working perfectly.
It may takes a while for setup and installing but once its installed it will be light weight and I promise you'll be pleased while working on it =)
Here is the link:
genymotion intallation user guide,
genymotion website

Every file of Project Unfortunately Blank while deleting .metadata folder

I am stuck with biggest problem now. My .metadata folder is deleted unforunately. after that i have tried to import again but all Project is going to blank. No one file has code.
What can i do? please help.

If you've deleted your (I assume Eclipse?) workspace folder and you have no way to recover it (have you tried the recycle bin/trash, deeper data recovery methods, etc.?), then your work may just be lost.
This seems like a good time to suggest integration of version control into your regular workflow. Git in particular is a pretty popular system these days.

Running decompiled file

I was working on an Android app but yesterday my Hard disk got crashed and all the data has been gone. What I'm now left with is a .apk file which I kept as a back up. I somehow managed to get my code back from that .apk file but not sure of how to import the whole project in Eclipse. The source along with other folders like drawables, values, manifest etc are saved in one folder. Any help would be highly appreciated.

I have two methods :
Download APKTool (url) and decompile your apk package. Here you have a tutorial.
After this you should can import your code into Ecplise.
Go to a specialist and try to restore your harddisk.
I hope I helped

ok, first of all, if you tried to decompile an app, I suposed you have used apk-tool or smali/backsmali tools for the code.
AFAIK you can't get your java code back. after decompile, you get smali code, which is some dalvik assembly language. I don't think you want to write apps in that.
If you were the developer of the app, you would've make a backup of your code, not APK. So, are you sure you're not lying to us?

R.java file not updating with UI element's id

I added some UI elements to the main.xml file in the res\layout folder and when I try to access them through the call, R.layout.my_uielement, the UI element that I created is not there. Even when I add a new xml file with UI elements, it still doesn't show up in the R.layout class. I have made checked the ids on them and they have the correct format (I think): android:id="#+id/my_button". What could be the problem? Do I need to compile the code first?
UPDATE:
I have already tried adb kill-server then adb start-server. It doesn't seem to help. I have also tried R.id.my_uielement, it doesn't register either.

This may not be the case for you, but sometimes when I use something from the android.R package (default android resources) and I use it in my class before making reference to anything from my own resource package, Eclipse adds the import android.R; statement in my imports. This will conflict with the default behavior of implicitly looking in your package's resources.
Check your import statements for import Android.R;. If it's there, remove it. And, if you're using anything from android.R, fully qualify it when you use it in code.

Clean project works fine. In Eclipse if you just change some xml components, it doesn't always generate a new R file. Cleaning does it.

Use R.id.your_ui_element, not R.layout.your_element

I faced this problem too. The R.java was neither generated nor updated.
If R.java is not generated when you create the project, run your 'empty` project. An R.java with references to resources will be automatically generated.
If R.java is not getting updated, Check for updates in Help -> Check for Updates
in Eclipse and update your SDK and ADT if required.

After 2 days I found a way to fix it...
I had saved half done project in my mail, so when R.java vanished i just replaced it with the old R.java file, this fixed a lot of errors, then made necessary changes and built the project(build it not clean)...I do not know whether clean and build performs the same job or not..but everytime i cleaned it , R.java used to go invisible...

Clean is working because it BUILD the project after cleaning. So the problem is ( at least it was in my case, because I switched off the Automatic Build a few days earlier ) that after you add an item or anything in a .xml file, the eclipse doesn't build it and can't refresh the R.java .

I've noticed that my R.java file is not always being properly updated when I add items to my strings.xml file or elsewhere. If I use a new value I added like R.string.newString the actual integer value might still be pointing to R.string.oldString or whatever (it seems to usually be the element directly above or below the new element in strings.xml but I haven't nailed down the pattern for sure yet).
You're not supposed to modify the R.java file, but it doesn't say anything about deleting it (not that I've seen, anyway). I've found that deleting R.java usually fixes my resource-related problems because Eclipse immediately regenerates the file with the integer values properly assigned.
Please note, I'm very much a beginner at Eclipse so I may not understand the consequences of deleting R.java but it seems to be working well for me so far. If what I'm doing is very bad, please let me know.

None of these worked for me!
The only way i can access an #+id/foo is by myPackage.R.id.foo.