[GUIDE][INDEX]How to modify an apk

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How to modify an apk

I’ve done several threads about how to theme and other similar topics but the info is sparse, so this ultimate guide/index will seat proudly in the theme section of XDA and will be updated when new things come, and as I learn more. This isn’t a beginners guide, I’m here trying to be as complete as possible, with links, references, ...
This initial version of the thread isn't here to stay, if you could contribute to this thread, it would mean the world to me, and would clearly help the community (of course I'll mention you for your contribution :) )

And keep at mind that I’m just an enthusiast, nothing more, and that this thread has been made only by me, so it's far from perfect. If I made any mistakes or if you want to add something please let me know.

Legal aspect:
Using this knowledge to infringe copyright is not only illegal, it’s detrimental to the community. The only legal case, and the only usage of this info condoned, is using it to theme OPEN SOURCE apps (because most of the time, commercial apps forbid reverse engineering in their policies). So don’t worry, theming AOSP is legal. You can always ask the permission of the devs for an authorization to customize their apps, make sure to ask before modding, and distributing the result.

Now I’m not a lawyer, but you can learn more on the legal aspect of reverse engineering on this Stackexchange post.

Summary of this thread:
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It's essential, almost mandatory, the Java Development Kit (JDK) and Java Runtime Environment (JRE) must be installed to use java based tools.

How to install the JDK and JRE
(download and follow the instructions, it’s pretty simple)​

Then, set the path to "java home", you need to do that in order to use java properly within your terminal:

To check if everything is okay, open a terminal anywhere and enter java --version. If it returns the version of the JDK and JRE you’re good.

B)Android SDK:
Unfortunately we aren’t able to download the Android SDK alone anymore, I used to consider it as a requirement, but now I don’t because some people don’t have the space to install the whole Android Studio IDE just to use the Android SDK.

I suppose that list is going to expand, those two above are the main ones, but if there's something else you need, I'll make sure to put it here ;)
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II-Download APKs

This sounds stupid to take one whole post for that, but sometimes it’s a drag, so here are some ways you can grab the apk you want to modify.

A)APKs form your phone:
Every app you installed from the playstore is under /data/app. With a root explorer like the excellent MiXplorer, you can browse to it and see the icons representing the apps on your phone.
There is an apk called base.apk, that’s the one you want.

Sometime there might be parts called split_....apk along with base.apk, for the excraction of those you’ll need tools like the amazing app called SAI (Split APK Installer), it’s a graphical interface so I’ll assume you’ll figure out how to use it yourself

B)From internet:
My two trusted sources I use: APK Mirror, XDA Labs (gone for now)
I also use this chrome module, it has simplified my life sooooo much, it’s provided by the APKmirror team: Toolbox for Google Play Store™

C)Your Sources:
If I missed any good and trusted website, let me know
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This is getting serious now.
If you want to modify the apk, you need to have what’s inside: the code.

A)Resources: Decompile Binary XMLs to Human-Readable XMLs:
We use APKtool for that, it decompiles the resources.arsc file to the res folder, and decodes binary XMLs to human-readable XMLs.
1-How to install APKtool:

2-How to use APKtool:
There are 3 main commands you need to know about:

apktool d [nameoftheapk].apk
Used to decompile the apk. There are several options you can use with that command, they're specified in APKtool's documentation (in the credits).

apktool if [nameoftheframework].apk
Used to set the framework files to decompile properly APKs. Usually some OEMs add framework APKs into Android for their apps to work, so we need to find and copy them, then “install” them with the apktool if command to APKtool. You can learn more about that on APKtool's website (in the credits).

apktoool b [nameoftheapk].apk
Used to recompile the apk. The final apk can be found inside the decompiled apk’s folder, in a subfolder named dist. You can also use various options with that command (listed in the documentation, link in the credits).

B) Decompile Classes.dex to smali:
APKtool also convert classes.dex files to .smali files, but keep at mind that you won’t be able to see the java source code in those files.
The .dex extention is for Dalvik Executable, which is very self-explanatory, and is also a binary format. APKtool turn them into .smali files, which are Human-readable files, not in java, but still! And if you want to modify the code, you’ll have to learn smali. (covered in the next part, good luck with that lol)

C)Read java source code :
There’s actually a way to see the java source code of an Android app, using some tools:
First turn the classes.dex files into .jar files with this command using Dex2jar:

./d2j-dex2jar.sh -f -o output_jar.jar apk_to_decompile.apk

(Execute the .bat if you’re on windows)

Quick explanation:

./d2j-dex2jar.sh: execute the dex2jar script
-f: replace the previous jar file named the same as output_jar.jar
-o output_jar.jar : set a name to the output jar file
apk_to_decompile.apk: name of the apk file you’re taking care of

Then read the jar file using JD-GUI (or any other java decompiler). It’s a quite simple software, lite weight, and you can download and run the java version without installing anything else.

Dex2jar isn’t updated anymore (since 2015), so there are errors when decompiling. You’ll be able to get a .jar file but it’ll be incomplete or not identical to the original one, that’s why this tool doesn’t allow one to modify java source directly. But you can get a great understanding of how this app works.

C) Nice tools from the XDA community:
• Tickle My Android (TMA) by @Ticklefish
A tool that ease the work with APKtool, amazing one!
• APK Easy Tool by @evildog1
Also works with APKtool, I don’t use it often, but it is great!
• Other tools:
Let me know :)

Credits, links for this part:
Stack Overflow Post
Documentation for APKtool
Another SO Post
@Rizal Lovins
" [Share Latest Apktool 4.2.2/Guide/Tutorial/] How to Decompile/Compile/Sign Apk/Jar "
@A_U ’s
" [GUIDE][HOW-TO] Decompile and Compile apps using Apktool in 5 Simple Steps "
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IV-What and how to modify
This part is gigantic, I'll try to include as much link as I can, this part isn't supposed to stay like that very long, as it contains very few of the hundreds of guide about theming in XDA. Help me out by suggesting some links.
A)Resources (XML):
To edit XMLs you can use whatever text editor you want, but I’d recommend Visual Studio Code. It has solid plug-ins that may come handy to avoid mistakes when editing.
You can also sort of visualize XMLs with Android Studio's Layout Inspector.
You have to open the apk’s folder in Android Studio and browse to the desired xml. Opening the resource manager will aslo allow you to visualize the XML files to a certain extent, but it's not cristal clear (see the screenshot) so I don’t use that very often, but it’s good to know.
Screenshot 2020-12-19 at 09.39.12.png

2-What’s xml
This subject is very long, you can learn a lot of things. Here are some links (increasingly detailed) to learn about XML:
You can modify deeply the UI by editing XMLs, here are some guides to make you familiar with some techniques. Again this is a very vast field, it deserve a thread itself, and this list clearly isn"t finished. Here are my favourites ones:
When modifying apks, some errors can be very frustrating, yet very easy to fix. Here are some usual cause of struggle:
  • Not properly set JAVA_HOME
  • The tools used (like apktool.jar) aren’t chmod +x (aren’t allowed to be executed)
  • You have to add java -jar [command] before every .jar tools commands for it to run
  • Tell me, don't be shy
For every tool related bug, please refer to their GitHubs, sometimes you’ll find a solution by searching. And XDA threads are also plenty of answers! (and if you’re really not lucky maybe stack overflow can help).

That’s a tough one. First, if you want my advice, editing them with Visual Studio Code and the smali plugin is way easier to find mistakes. There’s also a smali plugin for Android studio (and IntelliJ based IDE) made by Jesus-Freke, it is called smalidea.

Now I found one reaaallllyy awesome thread here on XDA about smali:
This is my reference, I’m still learning smali tho, this list may be updated, but this thread is pure gold, go check it out!

Credit for this part:
@Ticklefish , for XML 101 (but also for TMA), this is really one of my favourite thread on XDA
All the other members mentioned in the above list
@Jesus-Freke , for his work on smali, baksmali (integrated in APKtool) and smalidea
@Goldie , for the amazing thread explaining smali
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You've done the hardest part, now what's left is repacking that thing together.
A)How to recompile:
It’s pretty simple, do it with apktool with this command:

apktool b [nameoftheapk].apk
You can add several options, here’s the full list.
The -c option to me is the most useful, because it allows to leave the signature unchanged for system apks. It’ll be deprecated soon (APKtool v2.6.0), so you’ll have to do the trick manually.
What -c (--copy-orginal) does: “Copies original AndroidManifest.xml and META-INF folder into built apk. Scheduled for deprecation.”
A bit of details, good to know:
“META-INF contains apk signatures. After modifying the apk it is no longer signed. You can use -c / --copy-original to retain these signatures. However, using -c uses the original AndroidManifest.xml file, so changes to it will be lost.”


“After [d]ecode, there will be new folders (original / unknown) in the decoded apk folder
original = META-INF folder / AndroidManifest.xml, which are needed to retain the signature of apks to prevent needing to resign. Used with -c / --copy-original on build
unknown = Files / folders that are not part of the standard AOSP build procedure. These files will be injected back into the rebuilt APK.”

Apktool uses aapt2, the tool used in Android Studio to compile your app. You can learn more on what it is here.

First, remember that you can use aapt1 (used by default) and aapt2 when recompiling, try both if you run into some issues with the first.

If you have an issue with APKtool's dummy values, go on the Github Issue I opened, the problem is now solved.

Most common error, and simple to solve are the following:
-Name of the file not written correctly:​
brut.directory.DirectoryException: java.nio.file.NoSuchFileException: Firefoxr
Solution: The correct name is Firefox not Firefoxr, how dumb can I be?
-Aapt errors: (here a folder isn’t recognized):​
W:invalid resource directory name: /Users/Raiz/Desktop/apktool/Firefox/res navigation
Solution: Use aapt2, the folders not recognized are because aapt1 (used by default) is older than aapt2, so if you see an error like this, use the option “—use-aapt2”
-Xml Errors:
W: /Users/Raiz/Desktop/apktool/framework-res/res/values/styles.xml:1185: error: Resource entry Theme.Holo already has bag item textEditSuggestionItemLayout.
Solution: These errors are quite easy to fix, just go to the file at the line mentioned then fix the error. Usually it a doubled line, a synthax error, …

Unfortunately APKtool isn’t able to correct string typos, it’s up to you to write in correct English (definitely struggling with that on my side lol).

For other more specific errors, copy/pasting the error message in the google search bar will most certainly redirect you to a Github error, or a post in The Official APKtool XDA Thread. You can find answers by searching, so search thoroughly before asking, it’ll save you some time.

Credit for this part:
APKtool issues on Github
The APKtool documentation
@iBotPeaches for this amazing tool
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VI-Sign and Zipalign

We must sign an app after having modified it, so it can be installed properly on our devices. System Apps MUST keep the same signature they had before modifying, or else the app will continuously force close, and it may even result in bootloops and other bad things.
To keep the signature take the META-INF folder from the not decompiled apk (browse it as a zip file) and put it in the newly recompiled apk (browse it as a zip file too, if there is already a META-INF folder, just replace it)

Links to build and platform tool:
Build-tools: Have to be downloaded from sdk manager in android studio​

A)Official way:
Tool used in the correct order:
1)keytool (included inside java)
2)zipalign from build tools (29.0.2 here, but use the latest )
3)apksigner from build tools (29.0.2 here, but use the latest) (+the lib folder containing apksigner.jar)

Where are build tools?
Mac: ~/Library/Android/sdk/build-tools/[your buld-tool version]/
Linux: ~/Android/sdk/build-tools/[your buld-tool version]/
Windows: C:/User/yourusername/AppData/Local/Android/sdk/build-tools/[your buld-tool version]/

Disclaimer: Using jarsigner is also possible (tool natively included in java jdk), if you use it, make sure you zipalign AFTER signing.
Make sure that apksigner (and lib) as well as zipalign are in the folder you’re apk is in.
Make sure they’re all executable (check that using chmod) and on mac os, make sure your terminal has full disk access (I had a hard time figuring this out lol).
1-Generate keystore:
This is pretty simple, we’ll use keytool, at tool antively included in java jdk. We’ll need only one thing before using apksigner : the keystore.jks file (or a separate certificate and private key, but that’s more complicated)

keytool -genkey -v -keystore ~/Desktop/apktool/keystore.jks -alias Raiz -keyalg RSA -keysize 2048 -validity 10000

Just replace the alias (here Raiz) by a familiar name, you have to remember it! (here’s why)
Also replace the name of the jks file (but not it’s extension, even though it can be .keystore, I had less issues with .jks)

Quick explanation of what does what in the command:

keytool : the command to use keytool obviously
-genkey : generate the keystore
-v : display verbose
-keystore : set the path to the future file
~/Desktop/apktool/keystore.jks : Path and name of the future file, you can call the keystore whatever you want to.
-alias Raiz : specify the alias used, it can be whatever you want, but remember it, it’s like a publisher name
-keyalg RSA : specify the algorithm used for the key, here it’s RSA (here’s a bit of history)
-keysize 2048: the size of the key in bits
-validity 10000: validity in days, here 10000 days

1*- Generate key.pk8 and cert.pem:
This is a quote from another thread (by @wilskywalker), this isn't necessary, but can come handy when signing zip, so I'll leave that here anyway.
You will need the following download:
openssl genrsa -out key.pem 1024
openssl req -new -key key.pem -out request.pem
openssl x509 -req -days 9999 -in request.pem -signkey key.pem -out certificate.pem
openssl pkcs8 -topk8 -outform DER -in key.pem -inform PEM -out key.pk8

2- Zipalign:
./zipalign -v 4 firfox-mod.apk firefox-aligned.apk
Quick explanation:

-v : verbose
4 : align on 4 bits, putting another value will align the wrong way, just keep 4
firefox-mod.apk: name of the input apk, can be anything
firefox-mod-aligned.apk: name of the output apk, can be anything too

3-Sign the apk with apksigner:

./apksigner sign --ks keystore.jks firefox-mod-aligned.apk

Quick explanation:
sign: the command use to sign
--ks keystore.jks : specify the keystore file (the same one we generated seconds ago)
firefox-mod-aligned: the input apk (the one we just aligned), note that the apk will be signed and there won’t be any output apk this time

And you’re done, you can check that it has been properly signed with this command:

./apksigner verify firefox-mod-aligned

Where firefox-mod-aligned is the apk signed we want to check
3*-Sign the apk with apksigner using .pk8 and .pem files:

./apksigner sign ---key key.pk8 --cert certificate.pem firefox-mod-aligned.apk

Credits, links for this part:
How to sign an app (by Google)
apksigner documentation
keytool documentation
zipalign documentation
Stack Overflow post
@Rizal LovinsGuide

B) Unofficial ways:
Some amazing devs and contributors at xda provided us with tools to sign with ease APKs (without having to think about all of that),I didn’t fully tested every one fo them, but you can try them as an alternative if the “official way” didn’t worked out well.
Here they are:
APK easy tool by @evildog1
APK Sign/Zipalign/Install by @aureljared
Uber APK signer (Github)
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VII-Installing the apk
Your theme should be ready by now, but how do you want to install it?
There are several ways to get an apk inside your phone, I’ll go over the ones I think are the most common.

A)Regular apk install:
Just install it duh… (here you go if you need a little help).

B)Flashable zip:
I do recommend making flashable zips, because they’re pretty useful when installing modded system apps. So what is it?
A flashable zip contains 2 folders: META-INF and a folder which will mimic the path to the apk we want to install. Inside that succession of folders, we’ll put our modified apk, and when flashing, the modded apk (inside the zip) will replace the original one inside your phone.
E.g: create system/priv-app/systemUI/systemUI.apk to install a modified systemUI.apk file by replacing the original one
E.g: create data/data/com.mixplorer/databases/data.db to replace the original data.db file inside this folder
Once you get those folders done (and the apk inside of it), it’s time to write the edify script that’ll flash the zip file.

2-Edify Script:
Edify is the language the script will be written in.
The file containing the script is located in /META-INF/com/google/android/updater-script (the name of the file is updater-script, naming it something else would make it ignored by your custom recovery)
Open this document with a text editor, and start coding!

We want to copy/paste the content of our zips onto the system (and replace files), so here’s the precise things we’ll do:
a-(OPTIONAL)Your “intro”:
Using the ui_print(" "); command, we can make some really cool looking ASCII art. You can write comments at whatever steps you want with this command, it’s pretty handy!
ui_print("Your Message here");
b-Mount the system partition:
run_program("/sbin/busybox", "mount", "/system");

c-Extract the content of the zip to /system:
package_extract_dir("system", "/system");
d-Unmount the system partition:
This is very basic, you can do so much more with edify script! Set the progress bar progress, set permissions to certain files, delete folders and/or files,...

3-Sign your zip:
You need to sign your zip after compressing it! The process looks like the one with key.pk8 and certificate.pem files, so I'll refere again to the same thread for that. (In the Credits)

I've covered the basics, now it's index time, you can go further with the links in the credits, and you can suggest me more!

[WIP] How to Write an Updater-Script with Edify Code by @Karadorde
That one covers how to sign your zip:
[TUTORIAL] Making Flashable ZIPs, EDIFY Script, ZIP Signing & Key Creation [19.01.13] by @wilskywalker
My Very Own Script by Me

More Links:
[GUIDE] Create your own Flashable ZIP with custom updater-script and addon.d script by @Primokorn
[TUTORIAL] The updater-script completely explained by @KINGbabasula
4-How to make a working progress bar
First “create” the progress bar that can go up to 100%
show_progress(1.000000, 0);
Then set the progress after each steps: (here I set it at 10%)
Code: set_progress(0.100000)
C)ADB sideload:
Adb allows one to flash zips through command line using a custom recovery.
Now how to sideload an apk using adb:
  • Make sure your phone is plugged, and your PC allowed to use adb on your device. (the last steps of the guide I linked on how to install adb on your pc)
  • Reboot to recovery
  • For TWRP : Advanced → ADB Sideload For CWM : Install → Install Zip from Sideload
  • Code: adb sideload path/to/flashable.zip
And that’s it, congrats

D)Aroma Installer:
They’re very cool, yet I’m not really familiar with those.
This concept origins from XDA Inactive Recognized Developer @amarullz , and is used by the OpenGApps team for their Aroma package. Needless to say its work eased the task for many others, feel free to leave a thank on the threads:

Q’n’A about Aroma Installers: [Q&A] AROMA Installer - [Dev Move To DevDB]
Q’n’A about Edify and Aroma: (by @Dblfstr) Aroma, Edify, updater script Question and Answer thread
A tool to create them: [TOOL][3-10-13] Aroma App Package Creator v1.3.2 (by @commandersafi)
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VIII-Other ways to theme your device
Making the whole apk is often long, and doesn’t leave much control over the theme to the user, alternative ways of theming let users control how they want the theme to be applied. Those 2 ways won’t be covered by me (as I don’t know enough about them yet), that's why, for this part, every input in welcomed

A)Magisk Modules:
This is now a pretty common and convenient way to distribute APKs and mods, so I had to cover it. Here’s a link to an official developer guide, it covers a good part of it, if you have an input, it is welcome!

B)Substratum Themes:
I don’t even need to tell you what is substratum, as it is pretty famous (along with Magisk), but let’s say you’re totally new.
Substratum is a theme engine that allows you to control what element of your system you want to be themed, and apply themes with the possibility of disabling theme at some point in time. So how to make a substratum theme ?
Video from the XDA chanel on YT
Another one from XDA on YT
Theme template form the official Substratum Github
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Forum Moderator / XDA Welcome Team
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IX-Theming related topics
All of the things I couldn't fit in the previous sections are here, make an input, I'll make sure to add it if it's relevant ;)
A)Design Basics:
Now I don’t have especially fine taste in terms of designing, but I’m trying to learn!
Here are some links:
The Android Design Resources Forum in XDA
XDA Article about icon design
Matrial.io YT channel

B)Boot Animations:
Here are some helpful threads and links:
[TUTORIAL]How to make your own boot animations (with sound if you want) by @despotovski01
[GUIDE] How To Make Bootanimation by @jackeagle
[GUIDE][TUT]make/Port any bootanimation|||USING VIDEO/FRAMES by @deathviper

C)Icon Packs:
[GUIDE]How to create icon packs for Go/Nova/Apex/Holo/ADW/LauncherPro/XperiaHome by @iamareebjamal

D)Port OEM Apps:
[GUIDE/TIPS] How to Port OEM Apps / Vendor Apps to Your Current ROM by @Rizal Lovins , this one is a wealth of information! really good and unique

[Tweaks][Guide]Build.prop Tweaks by @bravonova
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Forum Moderator / XDA Welcome Team
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X-Not covered topics
Why don’t you talk about … ? That’s theming tho! And what about … and …? What is this thread!
I understand, these are legit claims, but I can’t cover everything. That’s where YOU come in play, you certainly know things that I don’t, so please, if you have any knowledge about something I didn’t mentioned above, please let me know!
I’m trying to make this thread as complete as possible, so I’d be very grateful if you could share a little about your knowledge ;).
Thank a bunch!

I know I already said that 10000000 times, but really, it would be awesome to have inputs!
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XI-Mods and Wallpapers:
Let me take a tangent from the original purpose of this thread. This was supposed to be all about guides, but I thought about that twice and I think that's a good idea.
Basically, this here will list some of the amazing mods and themes around xda.

The goal here is to crack open those and see how they work, this would represent an immense work that I'm not able to take on right now, so I may leave links here, and you'll do the jobs of understanding how they work. Maybe at some point I'll write some here (with the credits of the OP of course!), but certainly not now.

Offline Google LLC App Wallpapers by @[email protected]
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Senior Member
Thanks for this, useful for sure. This is mostly on Windows. There's a way to do this directly on the phone ( most of it anyway).
I use an app called: Apkeditorpro.
I use version 1.9.10 cause i don't like the ui in the newer version.
In it you can :
-edit xmls directly.
-decode the smali and edit them, and view the java code and edit it with no extra tools.
-extract or replace files
-and rebuild the apk when finished. It'll show you a list of compile errors if any when building to review. If the build works it signs it and offers to remove old app and reinstall the new apk.
I found it very useful in editing theme overlays or add fonts in fonts tab in settings.
I am like you an enthusiast in all things modding. Still learning smali/ java editing. Hope we can learn together and from each other👍
Merry Christmas 🎄


Jun 19, 2018
Hi I started working with Riru-Enhanced mode for Storage Isolation and some mistakes I made now it's oky now I want to try to modify the handset apk because Xiaomi Redmi 7 is andro system android carefully 🧐
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Forum Moderator / XDA Welcome Team
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04-01-2021 Update
The First Update of this thread is out!, check out the post I quoted to see the list of threads I added, I also integrated them to the main guide (with proper credits), but I think making a list for each update more convenient for you readers.
I recommend to bookmark those thread or to watch them, because some are really amazing!


Jun 19, 2018
[QUOTE = "Raiz, post: 84227321, membro: 8020437"]
Il primo aggiornamento di questo thread è uscito !, controlla il post che ho citato per vedere l'elenco dei thread che ho aggiunto, li ho anche integrati nella guida principale (con i crediti appropriati), ma penso che fare un elenco per ogni aggiornamento più conveniente per voi lettori.
Consiglio di aggiungere quei thread ai preferiti o di guardarli, perché alcuni sono davvero fantastici!
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