Develop Reference

Cannot resolve symbol SystemService

I am new to Android development, and was wondering why a library like AudioManager (android.media.AudioManager) can be used, but when I try to navigate to the code of AudioManager, half the source code is red.
For example, it says,
cannot resolve symbol SystemService"
Do I need to add some kind of dependency somewhere?
This means that when I debug through AudioManager, the bytecode does not match what appears on the screen and the debug is useless.
I've tried looking at other posts and changing my SDK version to 27 and my minimum version up to 23.
Thanks in advance.

This seems to be an IDE error, typically when I am getting build errors caused by this, Invalidate Caches and Restart will fix this. You can find it by searching in the help menu or under File in Android Studio

You could try below points as it worked-out for it :
Exit Android Studio
Back up your project
Delete all the .iml files and the .idea folder
Relaunch Android Studio and reimport your project
By the way, the error messages you see in the Project Structure dialog are bogus for the most part.

try to update your Android studio, they always working for something like this. I recommend AS 3.3

Thanks to all for trying to answer. I found the answer to my question here: The import android.os.ServiceManager cannot be resolved.
Explanation:
Apparently the reason AudioManager had so many reds is because it depends on many "hidden" classes, that are purposely excluded from the .jar libraries. The #hide in https://github.com/commaai/android_frameworks_base/blob/master/media/java/android/media/IAudioService.aidl is one example.

My android studio no longer formats code or predicts which classes I need imported. How can I fix this?

Previously, when a class was not imported, Android suggested I import them AND used to give resources a special format as in "R.id.aLayout". It has suddenly stopped and I am completely stuck, importing all these classes manually will be a real pain.

Please check if Power Save Mode is on or off in Android Studio .
If it is on turn it off.

Open File > Invalidate Caches/Restart & click on Invalidate and Restart
Note: Save your project before doing this.
Cheers :)

Cannot Resolve Symbol #+id/ in .xml when using android:below_

I try to add a button into my layout. The layout previously does not contain any errors. But after I drag and drop the button into the layout, it shows an error as the picture below.
Even I already define #+id/checksensortextview .
Here is the code before and after I add the button. (Even I remove the added button, the errors still there).
I add the button in activity_evaluate.xml, but it affect every .xml file except activity_login.xml
Is anybody face the problem like this before?
Thank you for any solutions and suggestions.

Invalidate Caches and Restart cleared that error for me.

Build clean resolve that question for me.

I actually just had this problem. Did you just move your project? Because I did. And it turned out that I had some old paths in your config files (idea and gradle configs).
I fixed it by copying my project folder to a new location and re-imported the project.
Hope it helps :)

I had the same issue I don't know what exactly can be the cause of this problem!
I fixed it by opening the xml file and going to Build then Recompile your_xml_file.xml.

I just had the same problem.
I tried to run my app, and it did, despite it was highlighted red. So looks like a bug - I relaunched android studio and everything was ok. Hope it helps

I did Build > Rebuild Project in Android Studio to fix the problem

Android Studio issue with R file

I was using Android studio now for a long time and it was fine. Recently, not sure what happened, but when I click on debug and have it perform make it complains about the R file and it seems like it doesn't generate it.
The only way it works is if I click on Build > Rebuild Project...problem is that it takes a long time for that to go through.
Is there anything I am missing? I updated the Android SDK tools, etc. as per some of the other suggestions?

Yes this is a known issue in the newest version of android studio. Google has suggested a temporary workaround until they can track down the problem and fix in next release. Turn off external builds in preferences > compiler. It might help.
Source: cannot resolve R into variable after Android studio update and R.java not updated after update to 0.1.6 .
Hope this helps.

Solution for android studio Users :
Goto : Menu tab - > Build - > Rebuild Project
after rebuild Project.R.Java file will be solve automatically ..

I was having the same problem, but it looks like a new update came out today. It seems to have solved the problem.

Try to import android.R, for every class you need R (of the package)
and then compile, it makes different error from before.
And remove all ('import android.R') , and rebuild it.
This trick is not for solving problem in proper way,
but makes the tool refresh.

And remove all "import android.R" , and rebuild it and import them again its working for me

Android studio suddenly cannot resolve symbol R

I was having a project open in Android studio. It was generated by the wizard and working fine.
I did some small changes to activity_main.xml and when I changed back to MainActivity.java i get the error in several places that it cannot resolve R. I might have done something to cause this. But I´m not sure what since it appered when I edited the xml.
Does anyone know what might be the solution to this?
I can find the R.java in r/release/packege/com/ and it looks fine.

Most of the time it is due to a bad XML file. XML files can be layout files, value files, or the Manifest file. Please check your xml files and try to rebuild the project. Sometimes cleaning the project and rebuilding it also works.

In addition, make sure you do not have a drawable with an invalid name. I had a drawable with a numeric filename and that didn't sit well with Android so it failed to compile R.java.

Downgrade Your Gradle Plugin Version
No amount of cleaning, rebuilding and restarting would do the trick for me.
The only thing that did the trick was downgrade our Gradle version from 3.4.0-alpha02 to 3.2.1.
So, instead of:
dependencies {
classpath 'com.android.tools.build:gradle:3.4.0-alpha02'
}
We used:
dependencies {
classpath 'com.android.tools.build:gradle:3.2.1'
}
After making that change and then doing a Gradle sync, everything worked.
Not sure if it's related to the alpha release or to that version or if changing your Gradle version at all just forces a refresh that otherwise cannot be done with the other commands, but there ya go.

Make sure in your AndroidManifest.xml the package name is correct. That fixed the problem for me when my R.whatever was marked red!

Try to clean the project by doing the following:
If you are using Windows, open CMD, cd to your project directory and run gradlew clean.

I just had this problem and the reason was that after editing the layout android studio automatically added an import to the source files:
import android.R
Of course the main R class has not all the symbols in your layouts, which made everything a red mess.
Removing that line solved for me.
EDIT:
Seems like eclipse had the same problem early on.

I sometimes get this after updating Android Studio. Not always straight away but after a while (perhaps after a restart of the program).
Here is what has worked for me: Tools - Android - Sync project with Gradle files.
For some reason just clicking the "Sync now" link that shows up after changing the build.gradle file has not done any change for me. Even though the messages says approximately the same thing.

I had the same problem because in my strings.xml I forgot to escape a apostrophe. Use " \' " never " ' " in xml file!

I had that same problem crop up, too (most recently while I was at lunch--came back and WTF?). And since this was a simple Hello, World program, there wasn't many places these errors could hide. The XML files looked fine--I hadn't even touched the manifest. A clean did nothing.
So I commented out a section of my layout.xml to try to narrow down the problem. Sure enough, the errors went away.
And then I simply UNcommented out exactly what I had commented...and everything was hunky-dory. Strange! Perhaps there was some lingering issues that needed to be touched in order to cause a rebuild of the layout file. You'd think basic stuff like that wouldn't happen these days, but they do.
One more thing! It's possible that something may happen to Java as well. It's very hard to know the status of the Java run-time environment; just easier to start again. So here's one more thing to try: restart your computer, restart Android Studio, AND THEN Invalidate Caches and Restart. Yep, the whole-hog.

When all else fails restarting android sometimes helps. During the start files are loaded afresh and this enables detection of the R

This problem occurs when you rename the package name.
After renaming the package name, you must change the older package
name to a newer one.
For me it solved the problem once I changed that.
After that, you might get errors in xml files, that you have to change
the package name there also.
That's it.

I just had the R problem and after a few hours found that the problem was my regional spelling as used in one of my xml files. The problem word was behaviour, which is spelled behavior by Americans.
I am Australian and we are taught ye olde English way of spelling certain words and so I looked past it a number of times before the penny dropped.
Its a small thing, but it can easily sneak up and bite you on the nether regions and is hard to spot and can waste a lot of time.

In my case I had just added some new image files to the drawable folder and accidentally put a GIF in there with my PNGs. I had not incorporated them into the project at all yet. I removed the GIF and then did a clean and rebuild. That fixed it for me.

I had this exact problem when importing a Udacity Example Program. The Message Pane in Android Studio said the error was failing to load a .PNG in a sub-directory deep in the Project Files.
Turns out the PNG with all of the sub-directory path names was greater than the name length limit defined by Windows 7 (260 characters). I gave the Project a shorter name - to free up some space - and then Android Studio happily compiled.

After you tried make project, clean project, rebuild project but still doesn't work.
Try restart Android studio