Please post the output of flutter doctor -v.

has anyone else had to deal with this? I am not able to build the project in android studio because of those missing symbols.

I found a workaround by adding the cached flutter.jar file as a library located in flutter\bin\cache\artifacts\engine\android-x64.

Not sure if this is the correct approach since it is the cached version and will need to be manually replaced each time, but it does resolve the symbols for me while editing.

https://stackoverflow.com/questions/25660166/how-to-add-a-jar-in-external-libraries-in-android-studio

this helped me.

I had to get the jar from flutter\bin\cache\artifacts\engine\android-arm instead of x-86

I found a workaround by adding the cached flutter.jar file as a library located in flutter\bin\cache\artifacts\engine\android-x64.

Not sure if this is the correct approach since it is the cached version and will need to be manually replaced each time, but it does resolve the symbols for me while editing.

In order to resolve flutter dependencies in Android Studio, we need to a flutter.jar file from the flutter project. I also did the same. But, Is it a good way to do it? @zoechi What effect can it have on our flutter project apart from size?

I had the same problem but then I found out that the flutter plugin package is recognised when you open the example/android folder in Android studio. Now I can build the project and I can unittest my plugin from Android studio without adding the flutter.jar.

What I did step for step:

1. delete the .idea folder in the project (do not know if is needed but just to be sure)
2. in Android Studio click on 'Open an existing Android studio project' and select the folder your_plugin/example/android

If you want to build your library through gradle you can run ./gradlew :your_plugin:assembleDebug

I had the same problem but then I found out that the flutter plugin package is recognised when you open the example/android folder in Android studio. Now I can build the project and I can unittest my plugin from Android studio without adding the flutter.jar.

What I did step for step:

1. delete the .idea folder in the project (do not know if is needed but just to be sure)

2. in Android Studio click on 'Open an existing Android studio project'  and select the folder `your_plugin/example/android`

If you want to build your library through gradle you can run ./gradlew :your_plugin:assembleDebug

I guess this is the proper way for now

I'm also having the same issue, I'm trying to add flutter to our existing gradle project, it's a really big project.
The flutter plugin need to include another local library which has the platform feature to be used but since gradle can't see the flutter sdk dependency the code does not compile... I don't understand why the flutter team does not provide gradle dependency for the flutter sdk...
We really want to move our ios and android project to flutter its seems that the tooling is not ready yet...

For those who are confused, why opening the the your_plugin/example/android would allow you to fix this issue and continue editing your plugin, here is the explanation:
#11632
Basically, when you open the example/android module, the gradle script will simultaneously attached the plugin directory in the current project and you can edit from there.

This structure is not great if you want to integrate it to another native project.

This break the following use case :
Mutlit module android root project -> flutter module <- flutter plugins.

If a flutter plugin need to access native features provided by a module in the root project. including the module in the flutter plugin settings.gradle won't work.
The flutter example app won't compile.

The only easy solution would be to publish the module to mavenLocal and then access it in the flutter android library build.gradle...

I still face the same issue in August 2019

[√] Flutter (Channel beta, v1.7.8+hotfix.4, on Microsoft Windows)
[√] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
[√] Android Studio (version 3.4)

Same issue. Importing flutter.jar fixes resolving, but then project fails to build.

@zoechi some issues should not be prioritized by how many likes
This issue face only library maintainers, not general users so likes will not be too much however it is an important issue

Have the same problem:

Plugin folder is inside the main project root, i'm unable to debug my plugin with native Android code.
I can import the flutter.jar in the plugin, but then the main project won't build

[✓] Flutter (Channel stable, v1.7.8+hotfix.4, on Mac OS X 10.14.6 18G87, locale en-GB)
 
[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
[✓] Xcode - develop for iOS and macOS (Xcode 10.3)
[✓] iOS tools - develop for iOS devices
[✓] Android Studio (version 3.5)

I see in local properties there is a flutter.sdk variable, with my local flutter sdk installation but it appears to be unused.
I tried to use this variable in the build.gradle file, but got similar errors as importing the flutter.jar file.
P.S. i had the same problem, so i created a new plugin project, but nothing changed

@davidBarbieri just use this line and comment it when you start building
//implementation files('D:\\Programming\\Android\\Tools\\Flutter_SDK\\bin\\cache\\artifacts\\engine\\android-x64\\flutter.jar')

https://github.com/amorenew/flutter_zkteco_fingerprint/blob/master/android/build.gradle

Any solution for this issue ?

As I understand the issue, Android Studio can't find dependency to flutter SDK. A solution which works for me based on this issue - #18983
So, to correctly setup flutter<-->android project you need

1. add to local.properties file
   flutter.sdk=/Users/<user_name>/development/flutter Flutter SDK home
2. add to build.gradle file

def localProperties = new Properties()
def localPropertiesFile = rootProject.file('local.properties')
if (localPropertiesFile.exists()) {
    localPropertiesFile.withReader('UTF-8') { reader ->
        localProperties.load(reader)
    }
}

def flutterRoot = localProperties.getProperty('flutter.sdk')
if (flutterRoot == null) {
    throw new GradleException("Flutter SDK not found. Define location with flutter.sdk in the local.properties file.")
}

...<your Gradle script>

apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"

...<your Gradle script>

flutter {
    source '../..'
}

After manipulation above, flutter.jar library should be connected with your project and imports should be available.

cc @devoncarew

Thanks @keenawl, your commit is a good example of how to fix this.

On Windows, I also had to define FLUTTER_ROOT environment as it still needed this even though flutter.sdk was defined and read from local.properties was defined.

Also changing the source to be:

flutter {
    source '..'
}

means it can build in VSCode and Android Studio. The ../.. path breaks the gradle build in VSCode for the example.

@dkaera....You my friend, are a genius...

Unfortunately not. The current workaround I use is that I open the /example folder of the plugin and copy there the content of myplugin.kt in the MainActivity.kt. edit there and copy the changes afterwards into the plugin.kt and reset the MainActivity.kt. a very strange process, but the only one that currently works for me.

Why is this so hard? Why is this 2 years old? Why am I unable to use my google editor for a google sdk that is supposed to support this? None of the workarounds work here. Can we talk solutions?

As for now, the temporary workaround mentioned in this link works: https://stackoverflow.com/questions/46289542/flutter-dependency-in-java-plugin

This method resolves the problem. But comment the implementation line in build.gradle file after building the plugin. If you run the example app without commenting the line, it produces Duplicate dependencies error as the flutter source is included in the example app's build.gradle file.

This workaround is working for me. Go through the link and try the steps. Also, comment the implementation line after building the plugin.

Instructions from a new plugin, with android platform code:

1. Create a new plugin using the template: flutter create --org com.example --template=plugin --platforms=android -a java sample (in the screenshots, I named it mackall_example, so that is what will show up).
2. Open the <Rest of path>/sample/example/android subdirectory in Android Studio:
3. You should see the following in the "Project" section:

4. From <Rest of path>/sample/example, run flutter build apk --config-only to generate the necessary config files. Note flutter run or flutter build while targeting android would also suffice.
5. Sync your Gradle files in Android Studio (on mac, this is File>Sync Project with Gradle Files).
6. You should now see the following, with dependencies resolved correctly:

@gmackall

You sir are a life saver. Thank you so much!

@gmackall You really save my life! Thank you.

I have done the same steps @gmackall has suggested. but still, I'm able to see different structures.

Damnn Got the same error again after a year. I have been building a big project and suddenly one day the android folder started appearing in red, everything was fine before.

Folder structure

Error:

Tried as many suggestions to solve it but failed!

The solution is just to open the example/android project that one includes the plugin itself. Crazy that this is still a thing.

Hi @Nilav2608 and others facing the same issue, the only possible solution which worked for me was to edit the plugin related files from within the following path :
<flutter-project>/example/android

Also, if you previously tried accessing the android folder within your flutter app i.e <flutter-project>/android in android studio then (although according to me it didn't make any difference) as suggested you should delete the existing .idea folder within that as well to prevent any conflicts and then restart android studio thereafter opening <flutter-project>/example/android

Thanks @Ldev007 , that's the only solution which helped me

1. Open the example/android
2. Navigate to the main plugin package in the left menu and edit the code.

If I open the sdk_ums_flutter/android directly, it seems not to see the Flutter libraries.

It's a shame, 6 years have passed, and this bug is still not resolved.

Thanks @Ldev007 , that's the only solution which helped me

1. Open the example/android
2. Navigate to the main plugin package in the left menu and edit the code.

How do you even get that plugin folder to show up?
I tried all the things like deleting the .idea stuff and building the project first, basically everything that is mentioned in the docs:

Step 2b: Add Android platform code (.kt/.java)
We recommend you edit the Android code using Android Studio.

Before editing the Android platform code in Android Studio, first make sure that the code has been built at least once (in other words, run the example app from your IDE/editor, or in a terminal execute cd hello/example; flutter build apk --config-only).

Then use the following steps:

Launch Android Studio.
Select Open an existing Android Studio Project in the Welcome to Android Studio dialog, or select File > Open from the menu, and select the hello/example/android/build.gradle file.
In the Gradle Sync dialog, select OK.
In the Android Gradle Plugin Update dialog, select Don't remind me again for this project.
The Android platform code of your plugin is located in hello/java/com.example.hello/HelloPlugin.

But I only get the App project...

我在Windows系统下遇到过相同的问题，似乎是项目代码和PUB的缓存目录在不同的磁盘分区导致的。通过PUB_CACHE环境变量将PUB缓存目录修改为和项目代码在相同的磁盘分区后恢复正常。

I've tried with different Android Studio versions (Koala rc, Jellyfish patch 2 and 1, Iguana) and different flutter versions (3.22.2 and 3.13.8) and I keep on getting the same unresolved errors.

I checked stack overflow(https://stackoverflow.com/questions/56965783/flutter-plugin-development-unresolved-reference-io) and all I can find is people saying to delete the .idea folder and open the android folder that is inside of my flutter project as a separate project in Android Studio, but still the lines stay red and keep the "Unresolved reference: io"

Also, when I have my flutter project open and navigate to the MyPlugin.kt file inside of the android folder that is in the root of my Flutter project it shows this message "Open for Editing in Android Studio", but when I click it nothing happens.

@yullg, can you explain the exact steps you've taken to do that and how that can be done on macOS?

yullg's message translated > I encountered the same problem in Windows system. It seems that the project code and PUB cache directory are in different disk partitions. After changing the PUB cache directory to the same disk partition as the project code through the PUB_CACHE environment variable, it returned to normal.

@SEGVeenstra found the solution, you will never guess, apparently if you read the documentation very carefully (😅 🤦‍♂️) You will succeed!

https://docs.flutter.dev/packages-and-plugins/developing-packages#step-2b-add-android-platform-code-kt-java

When creating a flutter plugin project called 'hello'

Before editing the Android platform code in Android Studio, first make sure that the code has been built at least once (in other words, run the example app from your IDE/editor, OR in a terminal execute cd hello/example; flutter build apk --config-only).

After that

Launch Android Studio.
Select Open an existing Android Studio Project in the Welcome to Android Studio dialog, or select File > Open from the menu, and select the hello/example/android/build.gradle file.
In the Gradle Sync dialog, select OK.
In the Android Gradle Plugin Update dialog, select Don't remind me again for this project.
The Android platform code of your plugin is located in hello/java/com.example.hello/HelloPlugin.

This worked for me!

@Code-Remote,

At this point, the plugin generation command should automatically run the extra flutter build apk --config-only command after generating the project.

I might found a nice workaround. Check my comment here: flutter/flutter-intellij#7487 (comment)

Do not open project/android, instead open project/example/android.