Develop Reference

How to extract source code from installed app?

I was developing an Android app for more than a month, but my computer crashed and I lost all the code from it. I have a compiled app installed on a test phone and tablet. Is there any way to extract source code from it?
I followed some guide for game modders (they are probably doing something similar), and I have extracted .apk with an app called Total Commander. Now the guide states that I should extract it with the apktool. But all files are still in binary (when I opened them I got random chars). Now, is there any tool (for Linux) that can decompile .apk back to source code, or maybe some feature of apktool I miss?
Note: I also tried this answer from 10 but also without success.
EDIT: javadecompileonline also did not decompile binaries correctly,
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First you go to Android studio's welcome page there is a option to extract source code from APKs.
Another way is to install this apk extractor application from play store then you can extract source code from APKs Link : https://play.google.com/store/apps/details?id=com.ext.ui

Encoding issue of AndroidManifest.xml file

I'm building phonegap app using phonegap-build.
I need to make some changes to the manifest of the android apk.
After i download the apk of my phonegap build, i rename it to .zip file to see the contents of the file.
When i open it, there i see the xml file there, and when i open that one, it has encoding problem.
This is what i see:
I understand it's a binary, but i need to see the content in plain english, if possible.
1) How can i encode it to see what is the content of this file properly?
2) After a change that i do on it, can i "decode" it back to binary?

So from what you wrote you wrote, you want to edit the AndroidManifest.xml from an APK file AFTER you built it, which is quite complicated. I suggest you editing the source AndroidManifest.xml and then re-building the APK. If you can't do this then please do the following.
(1) First, download and install Apktool. It is a free Android tool for decompiling and recompiling apps quickly. It provides access to .class files, resources and XML's. Here's a tutorial on how to install Apktool.
(2) Then you want to decompile your APK file (tutorial).
(3) Edit the AndroidManifest.xml file.
(4) Re-build the application (tutorial).
(5) Finally, you will have your APK file but it will be mostly useless as it is un-signed. You can't install un-signed apps as you will get an error (it may be possible to force-install it using root or adb tho) and you can't publish them. To sign it you can check out this link.
IMPORTANT INFORMATION: Your app will have to be signed with the same certificate with which it was signed the first time, otherwise it will be considered a different app. Not completely tho, you will have to un-install previous versions in order to install this one.
And yes, I know it's a very long and time-taking process but it is supposed to be, only if you have the source you should be able to edit the app.

As mentioned above, the tool you are looking for is Apktool.
You need to use --force-manifest flag when you decompile to decode AndroidmManifest.xml.

Can an APK be repacked after a minor text edit?

I'm creating a software that will guide the user through a few steps, to publish an android application (APK file).
The way I am doing this, is that the APK file is already compiled, and all I need to do is replace an XML file in the package, and that will change the behaviour of the application. My big problem now, is that unpacking the apk file, and doing any tiny text edit, and then packing it again, breaks the signature and prevents the application from running on any device, giving a message that the signature is incorrect.
How can I solve this? I want to safely open the APK, write something in a text file, and close it again. Note that this operation will be done on the user's computer (after he purchases our application) so we're look for a command-line tool with no special requirements like JDK.
Any help?

Ok I reached the best "tested" solution - I'm posting it here to save other developers hours of googling. The only downside is that I will require the customer to install JDK on his machine, unfortunately. The reason is because I did not find any apk-signing tool that works purely on windows, without relying on JDK.
I have my android application created using Air, so this makes things easy for me - all of the air files are treated as resource assets. So have your APK archive file ready.
Once you have your modifications ready, put them inside a temporary folder named "assets". You will use the 7-zip command line tool (free: http://sourceforge.net/projects/sevenzip/) to update the contents of your apk. To have it working with your apk you will have to rename your apk's extension to zip - don't worry, you'll change it back later.
Now from a .bat file (or directly in the command prompt) from the location containing both your apk file (zip extensioned) and your assets folder, you'll call: 7za u APK-file.zip assets
Now your apk file is updated. Rename it back to .apk extension
Now you'll use the signAPK tool from here https://code.google.com/p/signapk/ and note that this is the only step requiring JDK installed. It also assumes that you have your key files ready (replace the dummy ones included in the package). Extract the file contents and call: java -jar signapk.jar key.x509.pem key.pk8 [android_app].apk [signed_android_app].apk
At the very end, you may find your signed apk file size drammatically increased. So you need to use the android's zipAlign tool: (darn, can't post the link since new users can only post a maximum of two hyperlinks)
you will be calling the command: zipAlign -c 4 [signed_android_app].apk
And voila! That's the route I'm taking.
If someone finds a way to do the signing process without relying on JDK (assuming the key files are ready) please share.

How can I solve this?
You don't. If you modify an APK file, by any means, it must be re-signed.

Android apk files must be signed. That signature proves that the contents of the apk have NOT BEEN MODIFIED from what was initially published. (Which is exactly what you are doing.) The signature at the same time, also proves who the author is.
So in a normal signed apk file:
You know who the author is. (Even if it's not something you as a human can understand.)
You know the contents were put there by the author, and not modified since.
This is a key security measure built into Android, is there for very good reason, and cannot be overcome. It prevents things like viruses from being embedded inside innocent apk files.

Export apk from phone?

I compiled and ran a project on my phone through eclipse which is still install there currently. While doing some directory cleaning I accidentally deleted the source code so the only remaining version of the code is in the apk installed on my phone. Is there anyway to export the app back to my computer?? It isn't signed or anything either.
Thanks!

You can set up to be able to copy files on/off your phone via the USB connection - heres where you can look to find it:
Does Android keep the .apk files? if so where?
Then after you get the .apk off look at these questions for decompiling:
Is it possible to decompile an Android .apk file?
decompiling DEX into Java sourcecode

You CAN pull the APK off of the phone, but it's going to be Java Bytecode, not your source code (regardless of whether or not it's signed). You would have to reverse-engineer the classes to retrieve your code. If it's not a VERY large app, I'd say your time would best be spent simply re-creating it.

What's the difference between a regular Android APK and one included as part of a device's system image?

We have a manufacturer that wants to pre-install our application on their Android device. We sent them the APK and even though it installs fine when used by a user, it appears to not get installed correctly when included in the manufacturer's build image. FYI, our application uses the JNI layer and some libraries built with NDK. The exception we're seeing seems to indicate that the class loader cannot find the library and is unable to load it. They have verified that the library files are indeed present in the APK.
Since we dont make devices, its unclear why they are seeing this exception and what needs to be done differently when including a package as part of the Android build image.
Any Android folks here care to comment?

I have worked with pre-installed Android apps, that also uses library files, in my case jar files. I am assuming that you have added the appropriate lines to AndroidManifest.xml like <uses-library android:name..... I am also assuming that you have provided instruction on how to install your library files on handset, with instructions like adb push ... on the command prompt. If you havent, do provide them the instructions.
Another issue may be permissions, we had to get the library jar AND the permissions xml file installed, that may be the issue.
Also ensure that you are using the correct version of Android for testing. And if everything fails, ask them to send one of the handsets that is not working to you and you can then compare with the one in office and debug this. Good Luck, as all this can be pretty frustrating.

Besides moving the apk file into /system/app, you should ask the manufacturer to move the native libraries created by NDK (.so files) to /system/lib or the path specified by LD_LIBRARY_PATH.
Please refer to https://groups.google.com/d/topic/android-porting/r_Ao7_PWgKQ for more details.