问题
I've set up my project in Android Studio to use the Square Wire library, as per this question.
Build
-> Compile Project
works fine.
2:03:10 PM Compilation completed successfully in 31 sec
However, if I open one of my generated Protocol Buffer files, then the Square package is not being recognized.

Another symptom is that methods inherited from the Square Message
class are showing as "Cannot resolve method" compile errors in the editor, even though they build and run fine.

Do I need to do something more than just adding the dependency in build.gradle
for my module in my project?
回答1:
The following steps helps
- Close your project, and in your project folder delete
project/.idea
- Delete
~/.gradle
folder.
Open the project again. Everything should be solved.
回答2:
Thanks to free3dom for getting me on the right track here.
Diagnosis
The Sync Project with Gradle Files
option in Android Studio seems to keep the Project Structure
libraries up to date.

However, in my case there were some errors:

Expanding the (not very obvious) link showed the detail. My wire-runtime library was showing in an incorrect location:

This seemed to be a hangover from my original configuration where I had imported the JAR into a libs folder.
dependencies {
compile fileTree(dir: 'libs', include: '*.jar')
}
I subsequently changed it to be imported directly from Maven Central (as per here), and it seems that the old setting was never overwritten with the new one.
The Fix
The fix is to delete the library dependency from the Project Structure
screen and then Sync Project with Gradle Files
again.
More Detail
You can also see what path is being used to the resource by opening the .idea/libraries/wire_runtime_1_2_0.xml
directly.
My broken one was:
<component name="libraryTable">
<library name="wire-runtime-1.2.0">
<CLASSES>
<root url="jar://$PROJECT_DIR$/MY_MODULE/libs/wire-runtime-1.2.0.jar!/" />
</CLASSES>
<JAVADOC />
<SOURCES />
After deleting and re-adding the library it changed the root url
to:
<root url="jar://$USER_HOME$/.gradle/caches/artifacts-26/filestore/com.squareup.wire/wire-runtime/1.2.0/jar/44e7acbd5eb6f29698181dc3d67a60acf7efee80/wire-runtime-1.2.0.jar!/" />
Update
Android Studio v0.4.4 apparently fixes other bugs which have the same symptoms, so if you have an older version you may wish to upgrade.
回答3:
Simple Solution
Go through the link and it worked for me.
- Choose
File
option from menu on left top side of android studio. - Select the option:
Invalidate Cache/Restart
It will open an dialog. - Click on the first button with option:
Invalidate and Restart
- It will close Android Studio and restart it. Also, it will start re-indexing the project.
It resolved my problem
Go to File > Invalidate Cache/Restart > Invalidate and Restart
Source here for youtube
回答4:
1) Click on the gradle icon (right side on the android studio)
2) Click on the refresh button and wait for the issue to be resolved :D
回答5:
I was still having the same problem with Android Studio v3.2.1 constantly, and sorted out the problem just removing these two sub-folders of the .idea
folder (no need to delete the whole .idea
folder) while a gradle sync didn't work:
./idea/caches
./idea/libraries
回答6:
For me deleting .gradle and .idea folder of project solved the problem.
回答7:
My hacky fix for this -
- Open your
build.gradle
file - Cut out everything inside
dependencies{}
- Paste in notepad for super safe temporary keeping
- Choose 'Sync Now' in the
build.gradle
file - Wait for Sync to fail
- Paste your dependencies back in
- 'Sync Now' again
Tried a lot of solutions and this was the only fix for me.
回答8:
I had this problem after upgrading to Android Studio 3.1. I solved the issue by upgrading all the components I use. So I changed the following entries in my build.gradle (app):
Upgrade SDK (from "compileSdkVersion 25" to "compileSdkVersion 26" or maybe higher when you read this note):
//compileSdkVersion 25
compileSdkVersion 26
Comment: This change forced program to download/install new sdk during next sync.
Upgrade appcompat-v7:
//implementation 'com.android.support:appcompat-v7:25.4.0'
implementation 'com.android.support:appcompat-v7:26.1.0'
Upgrade firebase:
//implementation 'com.google.firebase:firebase-ads:11.4.2'
implementation 'com.google.firebase:firebase-core:12.0.1'
implementation 'com.google.firebase:firebase-ads:12.0.1'
In PROJECT build.gradle, upgrade google-services:
//classpath 'com.google.gms:google-services:3.1.0'
classpath 'com.google.gms:google-services:3.2.0'
Upgrade gradle (from 4.4 to 4.6). From gradle-wrapper.properties: distributionUrl=https://services.gradle.org/distributions/gradle-4.6-all.zip
After these changes, clean project, invalidate cache/restart, remove .idea/libraries content and resync (not sure about the order but ALL these activities solved the issue for me).
回答9:
Deleting libraries folder in .idea solved the issue for me. It is located in project's root/.idea/libraries.
I'm using Android Studio 3.1.4
回答10:
Just do this on your Android studio:
File -> Invalidate caches/Restart -> Invalidate and Restart
This worked for me. No need to clear ./gradle or ./idea folder
回答11:
Below steps when the Project is succesfully compiled but with unresolved classes (All classes usage will be in red color in all files)
Step 1. Delete .gradle file
Step 2. Delete .idea file
Step 3. Open new Android studio Window with some other android project on your system and close your Project with error
Step 3 . Now Open/Import the Project once again from the studio toolbar Android Studio ->File -> Open
Note: Now when you import the project the new .gradle and new .idea folders will be autogenerated with resolved dependencies by the compiler.
回答12:
If all above answers don't work for you. Just try update your dependencies to latest version. It worked for me.
回答13:
I tried most of the fixes above and what actually worked was deleting all the .AndroidStudio config folders and then restarting Android Studio.
- Location: C:\Users\your.username
回答14:
I found easy way
- Open app level
build.gradle
- Remove dependency which is showing error & Sync.
- Again add dependency & Sync.
Error Gone!
Before
After
回答15:
Deleting the .idea/caches
and .idea/libraries
should sort out all the errors.
回答16:
It seems that everyone uses a different approach for getting around these issues. I'll suggest another one that I feel is a bit less invasive than the others. When I introduce changes from an aar library that I include, I will open up the "settings.gradle" file for the project.
Then cut out the main project module from the list of projects:
include ':mainproj',
and then sync your project. Then paste it back in and re-sync your project once more. I believe that this is the same as some of the manual deletion steps, but this lets you do so from the IDE a bit quicker and less painfully.
回答17:
These solutions didn't help me with the same problem in Android Studio 0.5.8.
I described my answer to the same question (I guess): https://stackoverflow.com/a/23891829/534698 I just deleted ~/.AndroidStudioPreview directory (in Ubuntu). I missed all my Android Studio settings but it works.
回答18:
In my case, for some reason, Android Plugin Version wasn't set. I did try clearing cache and removing .gradle and .idea as well, but it didn't work out and after finally wandering for hours, I found this.
回答19:
I had a similar issue before, invalidating cache and restarting didn't resolve it. I just did a Gradle Sync and everything worked fine.
回答20:
Solved the issue by cleaning project Build->Clean Project
回答21:
For me, I refer a jar in a module library. It cannot resolve the symbol in the jar. So I find the solution for my situation. Use the provided
way.
provided fileTree(include: ['xxx.jar'], dir: '../moduleX/libs')
回答22:
All the answers above didn't work for me. My problem was that i had 3 modules, with 2 of them with the same package name.
It was ok for android studio <= 3.2.1.
For android studio > 3.2.1, ressouce was red.
I solved it like this mention here (i just made differents packages name for each modules ) : Any android Studio version > 3.2.1 show red resource but still compile
回答23:
I got the same issue cleared using the following steps:
update the library version in gradle to any random number, eg: lib_1.0.0 -> lib_1.0.0.0
gradle sync
sync shows error
revert the version change lib_1.0.0.0 -> lib_1.0.0
gradle sync
Open the java file with imports to see the error cleared.
来源:https://stackoverflow.com/questions/20226912/android-studio-inline-compiler-showing-red-errors-but-compilation-with-gradle-w