I would like to disassemble an Android application. Can anyone share any resource about the tools that are used?
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http://www.google.com/search?q=android+dissassembler
Please do not ask me to Google it I already have Google it and most of the results relate to hardware dissasembly not application
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khawasli said:
Please do not ask me to Google it I already have Google it and most of the results relate to hardware dissasembly not application
Click to expand...
Click to collapse
Yeah, right... It's really funny, I just clicked on my above link and all 10 results on the first page was about application disassembly...
Brut.all said:
Yeah, right... It's really funny, I just clicked on my above link and all 10 results on the first page was about application disassembly...
Click to expand...
Click to collapse
Yeah, honestly... Just Google this.
It's incredible how many people fail to use Google before they go around asking.
And, if you are looking to reengineer the files, Brut.all has the perfect solution in his signature.
Ok thanks guys
Sent from my HTC Desire using XDA App
I think the reason I am not getting the same results as you is because I live in a different region and Google results do differ according to region I dialed into vpn in the UK and git results of a tool called smali. I just ask kindly not to assume that anyone who asks a question a lazy person I feel that if someone simply said "check out smali" that would have been more productive. In my region smali comes out on the forth page of Google search
and you know what it might not even be the best tool out there maybe it is the best tool but not the best one with documentation or not the best one to start with... Google does not answer all those questions which is why I post on this forum because I would assume someone with good experience would give some good advice
So I would like to repeat my question anfmd would ask kindly for answers from experienced users in reverse engineering android apps
Sharing knowledge makes us all better of.
Sent from my HTC Desire using XDA App
khawasli said:
I just ask kindly not to assume that anyone who asks a question a lazy person
Click to expand...
Click to collapse
This is why I didn't write something like: "Oh, LOL, do you know, what Google is?", but simply gave you a link ;-)
Ok, smali is definitely the best one to disassemble the code - it's some kind of standard in the Android world. There are other code disassemblers, but they can't compete with smali.
If you want to look into resources (XML files mostly), then you need to decode them, cause they're compiled to binary code at build time. There is only one tool, which is able to do that: apktool, link is in my signature. Apktool contains smali to automate full decoding and building of an app, also it has few more features: you could check them out on project page.
There is also Apk Manager: it's a wrapper around apktool and other tools, it gives you simple GUI and simplifies some tasks, like installing an apk, etc.
WOW thanks a lot man that really helped, I got a very good idea now you rock
Related
I'm putting my theming project aside for now and get onto creating an app that I've always wanted to create that I do not see ANYWHERE in the market, forums, android websites, etc.
I've been reading and reading and reading different threads, instructions, etc. But no clue where to start. I've been reading on App Inventor but realized that it is very limited and I have my high doubts that App Inventor will not be able to achieve what I have in mind to make.
I've got the latest SDK and AVD Manager, JDK, Java, and have been using my emulator to test edited APKs. I'm pretty sure I'll be using my emulator to see how my app progress is coming along and see possible FCs and other issues and correct them as well as adding more to the app to make it even better.
But right now I'm stuck at where to begin here. Right when I was about to create this thread, I was making the name of the Title of this thread and was given threads relating to my title name and saw one thread that was sort of mentioning what I'm asking here.
I read the link provided in that thread ( http://developer.android.com/guide/topics/fundamentals.html ) and got some clues but just not enough to get me started here. I just need that push to get me going and eventually push it out to the market and make some money as a side project and learn from that and possibly make more useful apps. I cannot disclose my ideas here because then someone else (who has experience making apps) could take those ideas from me and go make it.
Is anyone willing to work with me here to get me started? I've helped countless people so it would be nice for a change for someone to help me out here.
There are so much Android development books on the market that I suggest to start with one of them. It's the best way to get some knowledge of the design principles used by the Android development framework.
Another method is to start with some examples found on the web. Just search for Android examples or something like that and you get tons of links
Another method is just to create something, get stuck and try to search for a solution (the most pragmatic method )
Yeah I know. That's why I'm constantly researching. I'm seeing some similarities between Java coding and building scripts in IRC (which I used to do, nothing big, just really small stuff). But my main problem is knowing what exactly are the main tools I need. I've had Eclipse for awhile but never used it. It has a lot of stuff in it and I get lost after a couple executions.
I'm just anxious to get started somewhere and get the momentum rolling for starters.
Could someone point me to a good book/ebook ? There are many out there but I'm sure that are some better than others...
If any french-speaker knows one in Voltaire's language, I'm in too. But English is fine...
DannyBiker said:
Could someone point me to a good book/ebook ? There are many out there but I'm sure that are some better than others...
If any french-speaker knows one in Voltaire's language, I'm in too. But English is fine...
Click to expand...
Click to collapse
Yeah, a good book (english) would be great. Can anyone recommend one?
You don't have to buy books but they do contain a lot more info in one book and would be better to have than trying to scour the internet and pull a bunch of infos together and try to put it together to understand step by step on how to get started and everything else.
Here's a link to a lot of android development books:
http://www.amazon.com/s/ref=nb_sb_s...pment&sprefix=android+application+development
Here's a link to some more info to getting started that is also useful:
http://developer.android.com/guide/basics/what-is-android.html
You may also need to get a Java coding book to help you put codes together properly and understand what each coding does, and tweaking them to work better.
Here's the link to Java coding for Android stuff for beginners:
http://www.amazon.com/s/ref=nb_sb_s...x=java+for+dummies&rh=n:283155,k:android+java
I just bought 2 books for Android application development and looking around for a good Java coding for beginners.
mdonova33 said:
Yeah, a good book (english) would be great. Can anyone recommend one?
Click to expand...
Click to collapse
professional android 2 application development by Reto Meier: http://www.wrox.com/WileyCDA/WroxTi...ication-Development.productCd-0470565527.html
Or, the Busy Coder's guide to android development by Mark L Murphy: http://commonsware.com/Android/
Last one is more written in a "let's get dirty" style. Really like that
TheSwaggeR said:
...
I just bought 2 books for Android application development and looking around for a good Java coding for beginners.
Click to expand...
Click to collapse
I think any java book will do, as long as it covers the principles of object oriented design and the data structures used by Java. You don't need any info about GUI programming in Java because that's all covered by the Android application framework.
The best Java books are the ones written by James Gosling et al, the designers of Java. But that may also be over the top for Android application development. Just some basic Java will do to get you started. The algorithms needed for basic apps aren't that complex.
App Inventor is a great tool to develop your android app. It simplifies the development and the editor is very intuitive.
Check out my blog on App Inventor and AppToMarket and a Workshop
http://Amerkashi.Wordpress.com
Hello people
I've wanted to make a Android app for a while now but I don't know where to start.
Can someone give me some pointers on where to start.
If it involves coding then be warmed I'm a complete novice at that.
No coding method: search Google for Android app inventor.
Coding and better method: Android apps use JAVA. Take some basic online courses, then learn the Android sdk. (functions that are specific to android)
Option b is better, and if you have a little patience it won't be too hard.
Sent from my ADR6400L using Tapatalk
alex ainsley said:
Hello people
I've wanted to make a Android app for a while now but I don't know where to start.
Can someone give me some pointers on where to start.
If it involves coding then be warmed I'm a complete novice at that.
Click to expand...
Click to collapse
If you want to get somewhere forget the app inventor and invest some time.
Start by using google on terms like "android tutorial" "android hello world".
Download eclipse and the android sdk (google has all the info and tutorial on how to do that).
The sdk has ALOT of very good example apps. From 3D drawing to system infos and interface layouts.
AAAAAAAAAAAAAAAHHHHHHHHHHHHHHHH Google app inventor is doing my head in.
if anyone is reading this on a scale from 1 to 10 how hard/complicated is making a app using coding?
Depends entirely on what you want the app to do unfortunately. If you can give some basic ideas of what you want it to do it will be easier to say how hard it will be.
well all id like my first app to do is when it starts up to show a picture with text then link you to a web page.
Nothing hard
Thats not too difficult, you could patch work something out of existing tutorials/example.
But its always relative saying how difficult something is.
It depends on the person...
Well sorry that's not helping much. I'm still at a loss on what to do.
Basically all you need to do is copy and paste the code from some tutorial examples, or you could even use the app inventor as you need barely any code to do this, for example:
http://developer.android.com/guide/topics/graphics/index.html
http://developer.android.com/guide/webapps/webview.html
Putting it all together and making it into an application shouldn't take you more than half an hour once you have gone through the starter tutorials to understand how and what it is you are using.
Ok I'll try that.
Click Here is the link for a LIVE remote workshop / presentation
-Cheers
omg
i really wanna learn, so i went to purchase course and
DescriptionsAmount
Diploma in Java Programming.Diploma in Java Programming.
$1,695.00Item price: $1,695.00
$1,695
are you serious??
Well if you are really determined to learn it, you can manage doing it on your own too, with the help of free online resources. Search for a tutorial series on youtube. Here's one I had found useful when I was learning:
http://www.youtube.com/watch?v=Hl-zzrqQoSE
You should also buy a good book on Java programming and read it. That would help a lot too.
read android developers guide
You can check android developers official site it has lot of tutorials and resources.
You can go to next university library and borrow any Android book. It will not include the latest version of OS, but it will have lot of fundamental information in one place, written by one person. Tutorails often show you how to solve single problem only.
Thank you
Also great video
You're Welcome! Yes it is a great video. That guy really does explain it nicely.
Is App Inventor still working?
Look also at cornboyz tutorial on youtube. Same guy, slightly different tuts
Hello everybody,
I am new to Android and web development in general. Recently Igot into a situation that is hard to figure out. I hope your professional advice can help me to solve the problem. A couple of months ago I realized that software dvelopment is a great way to earn money online. Making applications seemed to me the best way to have passive income streams bringing me cash from ads right into the pocket. I tried to code but it turned out to be so completely foreign to my mind and my nature, that I simply could not proceed.
Then, I decided to look for a company that actually develops software and knows how to do it. I found one company that looked legit and so we started working together. They created an app, implemented the ads and I uploaded it on the Android Market. It got really popular and I was so glad!
However, in a couple of months I noticed there was a new app that was EXACTLY like mine and it literally was stealling potential users that would choose MY app. I tried to contact the person but he said he had created the application before me. WTF! I saw he uploaded it AFTER I did.
What should I do? I see his app is increasing in downloads while mine is decreasing.
Report!! Perhaps???
Sent from my WT19i using xda premium
If I Have Helped You Can You Press
.
.
THANKS BUTTON
.
.
To support Me.
Welcome to the world of application development. Unless he literally stole your code, there really isn't much you can do about it. All you can do is to update your app to make it more appealing than his application. Have you also stopped to think that you two might be working with the same company? Double-dipping much?
prantoroy said:
Report!! Perhaps???
Sent from my WT19i using xda premium
If I Have Helped You Can You Press
.
.
THANKS BUTTON
.
.
To support Me.
Click to expand...
Click to collapse
Thank you. I pressed the Thank you button. I was thinking about it too but the thing is, how are they going to figure things out?
syung said:
Welcome to the world of application development. Unless he literally stole your code, there really isn't much you can do about it. All you can do is to update your app to make it more appealing than his application. Have you also stopped to think that you two might be working with the same company? Double-dipping much?
Click to expand...
Click to collapse
Thank you for your reply. Not many replied in my thread so I paticulary appreciate al the feedback I get
Is there a way to write an identical app ising a different code? I don't know about it.
Or, another qustion. Suppose he downloaded my app. How can he actually edit it? Does he use some sort of software? I was told, the apk file is like an archive that one can unzip and zip back again. But how would he do it, I wonder?
May be you are right and we are working with the same company although it's hard to imagine. There are thousands of companies in the world adn how in the world would we "meet" at one company? Here is thier website, by the way, may be it will help you to answer my questions --> a1qa website
May be you know better, I am a noob at software development, and I realize it.
Klaipedos said:
Thank you for your reply. Not many replied in my thread so I paticulary appreciate al the feedback I get
Is there a way to write an identical app ising a different code? I don't know about it.
Or, another qustion. Suppose he downloaded my app. How can he actually edit it? Does he use some sort of software? I was told, the apk file is like an archive that one can unzip and zip back again. But how would he do it, I wonder?
May be you are right and we are working with the same company although it's hard to imagine. There are thousands of companies in the world adn how in the world would we "meet" at one company? Here is thier website, by the way, may be it will help you to answer my questions --> a1qa website
May be you know better, I am a noob at software development, and I realize it.
Click to expand...
Click to collapse
You can easily unzip an apk file by using any Archive manager like WInZip, WinRAR , or 7-zip ... But can't actually make great changes like that ... But there is something called as Decompiling an apk, .. which will actually compiled the compiled java classes.dex file into .smali files... Now .. you can easily do some basic or sometimes even advanced changes to the app ... like for example .. you can change the app name by simply editing the string.xml in the res folder... then again recompile it into an apk and redistribute under a different name .. it's quite possible ... If you want to reduce the risk of such problems ... i'd recommend you have a look at ProGuard.
The ProGuard tool shrinks, optimizes, and obfuscates your code by removing unused code and renaming classes, fields, and methods with semantically obscure names. The result is a smaller sized .apk file that is more difficult to reverse engineer.
Click to expand...
Click to collapse
It is possible that someone can decompile your apk and read your source code if they had enough time and resources. If you are worried about such things you might have to begin using other techniques such as code obfuscation or encrypted compilers to protect your source code. And yes, it is possible to have two program do the same thing but have different source code to do it. Although there might be some parts that are the same, how you write you code will be different than how they write it.
You should be aware that making a lawsuit will cost you more money than you earned and if somebody makes something that does the same thing as you ddid, that still does not mean that they have stolen something from you. Jeez, how can somebody who hosts apps not know this, are you teenager or something?
Yes, in programming, it is possible to write programs in 50 different ways and do the same thing.
You cannot copyright ideas, only source code and functions...unless you are apple of course. They can copyright rectangular shapes.
What you should do? Get his app, and compare it to yours. I dont know if you can access source code in android apps because I dont develop aps yet, but if you can, you should compare his fuctions with yours. If the code is 80% simmilar, it is stolen.
Hi,
Looking for software to develop an app (preferably offline) which will help someone with no coding experience. I am proficient with photoshop & after effects but I don't know any coding.
I am sure at some point I'll require a pro to write some custom script for me but I want to get as far into the project on my own as possible.
I don't want to be bound by some websites hosting terms, with monthly fees and all this other stuff. Preferably, I'd build my app offline and go from there...I don't honestly trust these websites with little app builders then your app is stuck on their site and you're forced to use their hosting and things like that....if it's my app, it's my app!!! I shouldn't be bound to some website or whatever.
So, preferably offline app builder which someone with no coding experience can use?
carlitobriganteffs said:
Hi,
Looking for software to develop an app (preferably offline) which will help someone with no coding experience. I am proficient with photoshop & after effects but I don't know any coding.
I am sure at some point I'll require a pro to write some custom script for me but I want to get as far into the project on my own as possible.
I don't want to be bound by some websites hosting terms, with monthly fees and all this other stuff. Preferably, I'd build my app offline and go from there...I don't honestly trust these websites with little app builders then your app is stuck on their site and you're forced to use their hosting and things like that....if it's my app, it's my app!!! I shouldn't be bound to some website or whatever.
So, preferably offline app builder which someone with no coding experience can use?
Click to expand...
Click to collapse
http://www.appsgeyser.com/
Simple search would've showed this. The search button is very powerful and so is google.
What kind of application would you like to create? I could help you build or get you the tools for your app and teach you how to code.
Sent from ALCATEL One Touch Fierce
TagEHeuer said:
Simple search would've showed this. The search button is very powerful and so is google.
Click to expand...
Click to collapse
I promise you I've searched extensively and yet to find what I'm looking for. AppsGeyser lifts content from the net and turns it into an app...it remains on the appsgeyser site so doesn't really fit with what I'm looking for...I just want simple app creation software without having to learn code because what I'm looking to do isn't super-unique, it's just for an add-on to my existing business.
Has anyone ever used Wix for website creation for example?? Fantastic user interface, couldn't be simpler yet the possibilities are pretty much endless especially since you can add custom coding if you wish but I've built a few sites with Wix, all function great, all look fantastic...just a shame they don't have the same service for app creation.
Scripts said:
What kind of application would you like to create? I could help you build or get you the tools for your app and teach you how to code.
Sent from ALCATEL One Touch Fierce
Click to expand...
Click to collapse
It's pretty much just a local directory type app mate....that's why I mentioned above that I am really not trying to do anything unique so I'd imagine there's some nice editing software out there somewhere I could utilise and have my app designed and created pretty quick....like the above example of the Wix website,...you could have a fantastic looking website up and running in a couple of hours.
Anything guys?
Still looking for nice easy app production software.
Buy the Java reference book. Helped me a lot when k was starting out. Its some 1400 pages.
Books helped me the most especially with SQL. Consult me any time if you can't find your answer on Google cause frequently ur gonna be typing code bit have no idea what it does and how it works.
Also use Eclipse. Its like ms word for programmers with auto correct and hints and things that are very useful
Sent from my HTC first using xda app-developers app
---------- Post added at 07:53 PM ---------- Previous post was at 07:51 PM ----------
russian392 said:
Buy the Java reference book. Helped me a lot when k was starting out. Its some 1400 pages.
Books helped me the most especially with SQL. Consult me any time if you can't find your answer on Google cause frequently ur gonna be typing code bit have no idea what it does and how it works.
Also use Eclipse. Its like ms word for programmers with auto correct and hints and things that are very useful
Sent from my HTC first using xda app-developers app
Click to expand...
Click to collapse
Just pm me and ill tell you everything u need to know
Sent from my HTC first using xda app-developers app
russian392 said:
Buy the Java reference book. Helped me a lot when k was starting out. Its some 1400 pages.
Books helped me the most especially with SQL. Consult me any time if you can't find your answer on Google cause frequently ur gonna be typing code bit have no idea what it does and how it works.
Also use Eclipse. Its like ms word for programmers with auto correct and hints and things that are very useful
Sent from my HTC first using xda app-developers app
---------- Post added at 07:53 PM ---------- Previous post was at 07:51 PM ----------
Just pm me and ill tell you everything u need to know
Sent from my HTC first using xda app-developers app
Click to expand...
Click to collapse
Just sounds like thats way more advanced than I'm looking for dude.
I want build an app to ad onto my local directory business and it really isn't doing anything advanced or unique...it's the content that separates it's from other apps, not it's functionality....an app containing a load of menus with click through links (are these called hyperlinks?) to that section of the directory then linked again to open specific entries within that section of the directory....
Surely, there's a nice easy, almost drag and drop, design software out there I can use?
I'm really put off by these app builders I see that are $50 per month or whatever but if I have to go that way, ok. Thoughts? (Appreciate everyone's input and I know it can be frustrating talking to newbies that really don't have a clue so appreciate the input and patience folks!)
carlitobriganteffs said:
Just sounds like thats way more advanced than I'm looking for dude.
I want build an app to ad onto my local directory business and it really isn't doing anything advanced or unique...it's the content that separates it's from other apps, not it's functionality....an app containing a load of menus with click through links (are these called hyperlinks?) to that section of the directory then linked again to open specific entries within that section of the directory....
Surely, there's a nice easy, almost drag and drop, design software out there I can use?
I'm really put off by these app builders I see that are $50 per month or whatever but if I have to go that way, ok. Thoughts? (Appreciate everyone's input and I know it can be frustrating talking to newbies that really don't have a clue so appreciate the input and patience folks!)
Click to expand...
Click to collapse
U want a app=u code. No code=No app
Smack that thanks button if I helped!
Note 2 LTE powered by Illusion ROM and Plasma Kernel.
Sent from dat small country called Singapore.
Irwenzhao said:
U want a app=u code. No code=No app
Smack that thanks button if I helped!
Note 2 LTE powered by Illusion ROM and Plasma Kernel.
Sent from dat small country called Singapore.
Click to expand...
Click to collapse
I know enough to know that's simply not true...the reason for the post is that there's loads of drag and drop simple app builders out there that require no coding whatsoever....the point in the question is what is the best one and also the embedded question of why are there monthly charges that have such a huge range?
So, no...no code does not = no app.
carlitobriganteffs said:
Just sounds like thats way more advanced than I'm looking for dude.
I want build an app to ad onto my local directory business and it really isn't doing anything advanced or unique...it's the content that separates it's from other apps, not it's functionality....an app containing a load of menus with click through links (are these called hyperlinks?) to that section of the directory then linked again to open specific entries within that section of the directory....
Surely, there's a nice easy, almost drag and drop, design software out there I can use?
I'm really put off by these app builders I see that are $50 per month or whatever but if I have to go that way, ok. Thoughts? (Appreciate everyone's input and I know it can be frustrating talking to newbies that really don't have a clue so appreciate the input and patience folks!)
Click to expand...
Click to collapse
Eclipse allows drag and drop bit you're dreaming man. There is no way you can make anything work on android when making an app without knowing some basics of code.
So get that book I told you about, get eclipse, and get the book "hello android" which helped me start out.
Android apps are way more complicated than they seem bro
Monthly charges is because to make app building software is so damn hard. Trust me. Try your hand at old school app development. You will learn to appreciate app makers cause no joke its hard as hell
Sent from my HTC first using XDA Premium 4 mobile app
carlitobriganteffs said:
Hi,
Looking for software to develop an app (preferably offline) which will help someone with no coding experience. I am proficient with photoshop & after effects but I don't know any coding.
I am sure at some point I'll require a pro to write some custom script for me but I want to get as far into the project on my own as possible.
I don't want to be bound by some websites hosting terms, with monthly fees and all this other stuff. Preferably, I'd build my app offline and go from there...I don't honestly trust these websites with little app builders then your app is stuck on their site and you're forced to use their hosting and things like that....if it's my app, it's my app!!! I shouldn't be bound to some website or whatever.
So, preferably offline app builder which someone with no coding experience can use?
Click to expand...
Click to collapse
But question is that why any company offer you free tool that helps you to create app without coding knowledge. So only two option is here May be company offer paid tool for that and i think so no as such paid tool available in the market.
2nd option is company offer you online tool where you can create app without the knowledge of tool, in return companies want you to buy their subscription etc... to use that code.
I used some tools for testing person and some of them give you .apk and .ipa file to test your app on device but do not give you source code of app. You can read more about 4 best app building softwares, but as i mentioned that they do not give you source code.
I hope so above mentioned information helps you.
Please don't forget to thumb up button if it is helpful. Thanks
Not long ago, people / businesses in the UK would have to pay at least £12,000 for the development of a simple website, without administration / hosting / commerce functions, etc.
Now, you can produce professional websites yourself with a little cost and effort. Downloading free templates, Adobe Muse, WebPlus X8, etc.
Adobe have now launched DPS (Digital Publishing Solutions) which will eventually become a standalone, offline solution for people that want the ability to create apps on an offline basis, with a one-off cost (no monthly subscriptions).
Without a doubt, such offline app dev software is in development now, and I cannot wait until it arrives.
For now, I use HTML5 based WYSIWYG solutions which work well in good wifi / 4g connection, but with no App Store listing and no ability to push notify, but I can create these without subscription / cloud based resources.
It suits clients that have a user base that would generally be within good connection areas and require their services in such a place.
I am beginner and want to learn that how I can become android modder. So, I can mod android OS and apks?
It's just like being an interior designer. There isn't any requirements.
Just get your business cards printed and go for it!
So.. you're here just to advertise that site of yours?
Lame...
CXZa said:
So.. you're here just to advertise that site of yours?
Lame...
Click to expand...
Click to collapse
nope dude I actually want to learn. I mean to say that which language should I learn?
Java is as good as any. Once you learn one you can do others too...
CXZa said:
Java is as good as any. Once you learn one you can do others too...
Click to expand...
Click to collapse
Thank you very much
andromodguide said:
Thank you very much
Click to expand...
Click to collapse
EDIT: Ok, now I see what type of modding you were talking about. XDA is not the place to request such knowledge, as it's basically the same as a warez request. The website you have in your signature, idk if you're part of this scam or not, but seriously, GTA 5 apk mod... this website is sooo sketchy. Please read the rules before posting.
Don't get me wrong, I'm disapproving the website, if you're not part of it, and just asked if you could learn how to mod an apk it's fine, it's just not at xda you should ask. But if you're part of this website advertising those fake apks that maybe used to hack someone's device, I think that's truly despicable.
I left my original answer down here:
Spoiler: ...
XDA is the place !
I personally don't know much java, and was unable to understand a word of english, so all of the tech documentation was a mystery for me. I just heard about one reverse engineering tool called apktool. So I set it up and started cracking open apks to understand how they really works from the inside by reading files and stuff. Then I came here (with a better knowledge of English and of what's an apk) and found many resources to learn. It depends on the kind of things you want to mod. If the UI is your priority, I'll advice you to start by understanding what's xml and how google uses it inside of every app. Eventually you'll have to learn java for more deeper tweaks, but to begin I think understanding how xml works is easier, and more practical since you'll have to modify that in order to change any UI element.
If you're after modding how the app works itself, then java is the first thing you should learn. (And don't learn any java, Android uses more the Java OOP).
I'll leave you some links for both ways of modding :
Modding UI (theming):
App resources overview | Android Developers
developer.android.com
I also did guide for theme using a simple method that doesn't require any prior knowledge of xml and stuff, and get you to play with the interface (like changing color and stuff):https://forum.xda-developers.com/t/guide-theming-how-to-theme-any-android-app.3777101/
Ticklefish is one good themer here on xda, he made some guides about theming that, even if they're old, can teach you a lot about xml : https://forum.xda-developers.com/general/xda-university/xml-101-xml-modding-easy-t2929816/
For the Java way:
I've seen many many java courses around the internet. Actually I can't tell you which one is the best or which one to avoid because I didn't learn java yet myself. Your on your own for that one, but good luck !