Develop Reference

Unknown attribute for known attributes in xml files

I recently installed Android Studio on my Desktop running Ubuntu 17.10. However, when I open any Android Studio Project or even create a new Project, while editing XML files, it wrongly displays an "unknown attribute" error. Normally, I wouldn't care, but this causes Android Studio to not give any suggestions for attributes which I need.
What I've tried:
Invalidating cache
Deleting the .iml file and rebuilding project
Rebuilding and cleaning project several times
Deleting gradle's cache
Updating Android Studio (Current Release is Android Studio 3.1)
Here is a screenshot of what's happening

Try doing a gradle sync. It should resolve the problem

I´ve tryed all the solutions but the only thing that worked for me was 4gus71n's answer.
Deleting the C:\Users.AndroidStudio3.2\system\caches folder solved my problem.
Link to his answer: https://stackoverflow.com/a/53160674/6568421

Use project's SDK not Android's SDK. You can edit SDK Location in local.properties file

I had faced similar issues and all the above also did not worked for me.
If all else failed, do a clean install of android studio. You need to do a clean installation because if you just uninstall and install again, some of the files still remains in your system. It did not work for me when i just uninstall and install android studio. The clean install worked for me and I believe it should solve most of the problems.
I faced this error probably because i installed an entire android project but I am not very sure what is the exact error that caused this problem.
For clean installation, you can look at this links for windows and mac
How to completely uninstall Android Studio from windows(v10)?
How to completely uninstall Android Studio on Mac?

How to resolve Android Studio cannot find JAR 'core-3.1.1.jar' required by module 'gradle-jetty?

I opened up Android Studio today and for the first time I saw this error:
Error:Cannot find JAR 'core-3.1.1.jar' required by module 'gradle-jetty' using classpath or distribution directory '/Applications/Android Studio.app/Contents/gradle/gradle-2.14.1'
I have tried, restarted both my Mac and Android Studio but yet I still get this error. Can anyone help me?

I had the same problem, follow the answered detailed here to uninstall, and then just re-install. Before importing any existing projects just create a dummy project to ensure that everything finishes installing correctly.
Then simply just tell your antivirus that the project folder for android studio is excluded from the virus searches.

It turns out my antivirus had removed the file.
An uninstall and fresh install of Android Studio was able to solve my problem.

I have the same problem. Yeah, my Antivirus deleted the file too but it's seem uninstall and re-install Android Studio didn't work for me.
After re-install Android Studio, I can work normal with 1 project but when i try to open other project even create a new one, the 'core-3.1.1 jar' error show up again.

Just remove ./gradle folder compeletely.
Let Android Studio install Gradle from new or do it yourself.

Android Studio error: This folder does not belong to a gradle project (Jsoup.jar)

Since last android studio (1.1.0) update I have one issue with Jsoup(1.8.1) Gradle and it compilation.
When I import jsoup.jar in the projects I receive a message that said
To fix this problem. I have tried:
-I try click on "Add now..." but dont fix the issue.
-Clean project.
-Rebuild project.
-Close and open Android Studio.
Nothing have worked.
Any ideas?
Thanks.
Update 1: I have updated to android-studio Beta(1.2) and now works fine. But i want use android-studio Stable version.

I had the exact same problem. On Mac OS X 10.10.3, upgading to version 1.2.2 of Android Studio solved this problem for me. I used option-return key press while hovering over the class name I wanted to reference and that caused Android Studio to add the appropriate import. Auto-completion seems to work as well in the IDE.

Gradle home can not be found - Android Studio

I am new to Android Studio and Gradle. Everything was working perfectly fine but suddenly Android studio has started to give me the following error when I run the project (no problem in building the project):
Error running build: Gradle home can not be found
I'm on a Mac OS X and I have already tried to follow this article to add Gradle home to my system PATH variable.
I am also assuming this happened after my latest update to the Android Studio.
Can anyone please help me figure out what might be causing this as I have tried to search a lot with no luck.
Thanks.

Android Studio doesn't launch: Could not find or load main class com.intellij.idea.Main

Being new in Android devopmnet, I have been using Android Studio for development, but suddenly it doesn't work anymore.
The program doesn't launch anymore, and If I execute the studio.bat from Command Prompt, I get the following error:
Error: Could not find or load main class com.intellij.idea.Main
I have seen other posts about Android Studio not launching (e.g. this and this), but neither of them solve my problem. I have set PATH variables for both JAVA_HOME and JDK_HOME correctly to C:\Program Files\Java\jdk1.7.0_07
As I have mentioned, Android Studio used to work and I don't have any idea why it has stopped working. Any clue?

For android studio 1.3.1
go to environment variable and create new variable and give it a name JAVA_HOME and in path use this C:\Progra~1\Java\jdk1.7.0_71.
I hope that can help you.

if you have just used copy paste of exe file it will show this message so go in Program Files\Android\Android Studio\bin and click on exe file.

I had the same issue after updating the Android studio. I was not able to launch it from click on Android Studio icon and after running ./studio.sh it was giving me same error
I follow the below step and solved the problem.
I downloaded the studio and install it in the new directory.
After installation success, copy all the files & folders and paste and replace it into old location where studio was installed.

Having JAVA_HOME set to point latest JDK version (C:\Program Files\Java\jdk1.7.0_79) will make the Android studio work. Make sure the path is correct. Seems that JDK_HOME is not needed.
can refer Installing Android Studio (Not working)

If you have recently uninstalled and reinstalled Android Studio and had previously pinned the Android Studio icon to your Task Bar or Start Menu, it may be that this icon no longer looks for the new installation.
Delete it and re-pin it and all will be fine.

I faced the same issue while launching the studio.exe file. The actual problem was I have downloaded the 64-bit version of Android studio. But my computer supports only 32 bit.
So I downloaded 32-bit version and installed.
Now it is working fine.

Well after searching allover the web, failed to get solution till i decided to reinstall android studio. same folder changed nothing didn't delete anything just reinstalled and boom works as before

This happens when you update Studio and new version is installed and previous one is in process of deletion: at the main time if PC shut down or suddenly crashed due to power cut etc. Then this problem will appear:
could not find main class com/intellij/idea/main
Solution:
Go to this path "C:\Program Files\Android", there you will find two Android Studio Folders.
Find which one is latest: (Latest name wold be "Android Studio1") && (Old version would be Android Studio)
Delete old one(if you don't need it any more) and launch latest exe on this path:
C:\Program Files\Android\Android Studio1\bin

Open the Installer and download it again and you can select delete previous versions to clear confusion.

Open studio64 instead of studio

I found Answer: you just make wrong shortcut(just ctrl+C ctrl+v) for launchfile(exe). You must make shortcut following this method:
Right mouse click and select make shortcut menu.

Please follow the below steps,
Go to My Computer -> Properties -> Advance System Settings
System properties window will appear
Go to Advance tab -> Environment Variables -> New
Add or update JAVA_HOME path as expected.
Optionally you can also add or update JDK_HOME if you have JDK installed in your PC