flutter_unity_widget

Flutter unity 3D widget for embedding unity in flutter. Now you can make awesome gamified features of your app in Unity and get it rendered in a Flutter app both in fullscreen and embeddable mode. Works great on Android, iPad OS, iOS, Web.

Windows support is a work in progress.

Notes

Use Windows or Mac to export and build your project.
Users on Ubuntu have reported a lot of errors in the Unity export.
Emulator support is limited and requires special setup. Please use a physical device for Android and iOS.
Supports Unity 2019.4.3 or later, we recommend the latest LTS.
Use only OpenGLES3 as Graphics API on Android for AR compatibility.

Notice

Need me to respond, tag me Rex Isaac Raphael.

This plugin expects you to atleast know how to use Unity Engine. If you have issues with how unity widget is presented, you can please modify your unity project build settings as you seem fit.

Moving forward, versioning of the package will change to match unity releases after proper test. Mind you this does not mean the package is not compatible with other versions, it just mean it's been tested to work with a unity version.

Windows coming soon.

Installation

First depend on the library by adding this to your packages pubspec.yaml:

Flutter 3.0.0

dependencies:
  flutter_unity_widget: ^2022.2.0

Pre Flutter 3.0.0 (This version will gradually be deprecated)

dependencies:
  flutter_unity_widget: ^2022.1.0+7

Now inside your Dart code you can import it.

import 'package:flutter_unity_widget/flutter_unity_widget.dart';

You will need to open and export a Unity project, even for running the example. Your build will fail if you only include the widget in Flutter!

Preview

30 fps gifs, showcasing communication between Flutter and Unity:

Setup

In the tutorial below, there are steps specific to each platform, denoted by a ℹ️ icon followed by the platform name (Android or iOS). You can click on its icon to expand it.

Prerequisites

An existing Flutter project (if there is none, you can create a new one)
An existing Unity project (if there is none, you can create a new one).
A fuw-XXXX.unitypackage file, found in the unitypackages folder. Try to use the most recent unitypackage available.

Unity project setup

These instructions assume you are using a new Unity project. If you open the example project from this repository, you can move on to the next section Unity Exporting.

Create a folder named unity in your Flutter project folder and move the Unity project into there.
The Unity export will modify some files in the /android and /ios folders of your flutter project. If your Unity project is in a different location the export might (partially) fail.

The expected path is /unity/project-name/...

Make sure you have downloaded a fuw-XXXX.unitypackage file mentioned in prerequisites.
Using Unity (hub), open the Unity project. Go to Assets > Import Package > Custom Package and select the downloaded fuw-XXXX.unitypackage file. Click on Import.
Go to File > Build Settings > Player Settings and change the following under the Other settings > Configuration section:

In Scripting Backend, change to IL2CPP
(Android) Target Architectures, select ARMv7 and ARM64
(Android) For the best compatibility set Active Input Handling to Input Manager (Old) or Both.
(The new input system has some issues with touch input on Android)
(iOS) Select Target SDK depending on where you will run your app (simulator or physical device).
We recommend starting with a physical device and the Device SDK setting, due to limited simulator support.
(Web) Set Publishing settings > Compression format to Brotli or Disabled.
Some users report that Unity gets stuck on the loading screen with the Gzip setting, due to MIME type errors.

In File > Build Settings, make sure to have at least 1 scene added to your build.

Some options in the Build settings window get overridden by the plugin's export script. Attempting to change settings like Development Build, Script Debugging and Export project in this window will not make a difference. If you end up having to change a build setting that doesn't seem to respond, take a lookat the export script FlutterUnityIntegration\Editor\Build.cs.

Unity exporting

After importing the unitypackage, you should now see a Flutter option at the top of the Unity editor.
Click on Flutter and select the appropriate export option:

For android use Export Android Debug or Export Android Release.
This will export to android/unityLibrary.
For iOS use Export iOS Debug or Export iOS Release.
This will export to ios/UnityLibrary.
Do not use Flutter > Export Platform plugin as it was specially added to work with flutter_unity_cli for larger projects.

If you use git, you will probably want to add these unityLibrary folders to your gitignore file. These folders can get huge and are not guaranteed to work on another computer.

Proceed to the next section to handle iOS and Android specific setup after the export.

Platform specific setup (after Unity export)

After exporting Unity, you will need to make some small changes in your iOS or Android project.
You will likely need to do this only once. These changes remain on future Unity exports.

ℹ️ Android

Setting the Android NDK

If you have Unity and Flutter installed on the same machine, the easiest approach is to use the path of the NDK Unity uses. You can find the path to the NDK in Unity under Edit -> Preferences -> External Tool:

Copy the path and paste it into your flutter project at android/local.properties as ndk.dir=.
(For windows you will need to replace \ with \\.)
Don't simply copy and paste this, make sure it the path matches your Unity version!

    // mac
    ndk.dir=/Applications/Unity/Hub/Editor/2020.3.19f1/PlaybackEngines/AndroidPlayer/NDK
    // windows
    ndk.dir=C:\\Program Files\\Unity\\Hub\\Editor\\2021.3.13f1\\Editor\\Data\\PlaybackEngines\\AndroidPlayer\\NDK

With the above setup, you shouldn't have to define any NDK version or setting in gradle files.
If you don't have Unity on the device making your Flutter buids, you can instead define it in android/app/build.gradle.

android {

  ndkVersion "21.3.6528147"
}

To find the exact version that Unity uses, check source.properties at the NDK path described above.

Depending on your gradle version, you might need to make sure the minSdkVersion set in android\app\build.gradle matches the version that is set in Unity.
Check the Minimum API Level setting in the Unity player settings, and match that version.
(optional) Fixing Unity plugins.
The Unity widget will function without this step, but some Unity plugins like ArFoundation will throw mUnityPlayer errors on newer Unity versions.

This is needed for Unity 2020.3.46+, 2021.3.19 - 2021.3.20 and 2022.2.4 - 2022.3.18.
This requires a flutter_unity_widget version that is newer than 2022.2.1.

3.1. Open the android/app/build.gradle file and add the following:

     dependencies {
+        implementation project(':flutter_unity_widget')
     }

3.2. Edit your android MainActivity file.
The default location for Flutter is android/app/src/main/kotlin/<app identifier>/MainActivity.kt.

If you use the default flutter activity, change it to inherit FlutterUnityActivity:

// MainActivity.kt

+ import com.xraph.plugin.flutter_unity_widget.FlutterUnityActivity;

+ class MainActivity: FlutterUnityActivity() {
- class MainActivity: FlutterActivity() {

3.2. (alternative) If you use a custom or modified Activity, implement the IFlutterUnityActivity interface instead.

// MainActivity.kt

// only do this if your activity does not inherit FlutterActivity

import com.xraph.plugin.flutter_unity_widget.IFlutterUnityActivity;

class MainActivity: CustomActivity(), IFlutterUnityActivity {
    // unity will try to read this mUnityPlayer property
    @JvmField 
    var mUnityPlayer: java.lang.Object? = null;

    // implement this function so the plugin can set mUnityPlayer
    override fun setUnityPlayer(unityPlayer: java.lang.Object?) {
        mUnityPlayer = unityPlayer;
    }
}

The Unity export script automatically sets the rest up for you. You are done with the Android setup.
But if you want to manually set up the changes made by the export, continue.

Optional manual Android setup

Open the android/settings.gradle file and change the following:

+    include ":unityLibrary"
+    project(":unityLibrary").projectDir = file("./unityLibrary")

Open the android/app/build.gradle file and change the following:

     dependencies {
+        implementation project(':unityLibrary')
     }

open the android/build.gradle file and change the following:

allprojects {
    repositories {
+       flatDir {
+           dirs "${project(':unityLibrary').projectDir}/libs"
+       }
        google()
        mavenCentral()
    }
}

If you need to build a release package, open the android/app/build.gradle file and change the following:

     buildTypes {
         release {
             signingConfig signingConfigs.debug
         }
+        debug {
+            signingConfig signingConfigs.debug
+        }
+        profile {
+            signingConfig signingConfigs.debug
+        }
+        innerTest {
+            matchingFallbacks = ['debug', 'release']
+        }
+   }

The code above use the debug signConfig for all buildTypes, which can be changed as you well if you need specify signConfig.

If you use minifyEnabled true in your android/app/build.gradle file, open the android/unityLibrary/proguard-unity.txt and change the following:

+    -keep class com.xraph.plugin.** {*;}

If you want Unity in it's own activity as an alternative, open the android/app/src/main/AndroidManifest.xml and change the following:

+    <activity
+        android:name="com.xraph.plugin.flutter_unity_widget.OverrideUnityActivity"
+        android:theme="@style/UnityThemeSelector"
+        android:screenOrientation="fullSensor"
+        android:launchMode="singleTask"
+        android:configChanges="mcc|mnc|locale|touchscreen|keyboard|keyboardHidden|navigation|orientation|screenLayout|uiMode|screenSize|smallestScreenSize|fontScale|layoutDirection|density"
+        android:hardwareAccelerated="false"
+        android:process=":Unity">
+    <meta-data android:name="com.xraph.plugin.flutter_unity_widget.OverrideUnityActivity" android:value="true" />
+    </activity>

ℹ️ iOS

Open the ios/Runner.xcworkspace (workspace, not the project) file in Xcode, right-click on the Navigator (not on an item), go to Add Files to "Runner" and add the ios/UnityLibrary/Unity-Iphone.xcodeproj file.

(Optional) Select the Unity-iPhone/Data folder and change the Target Membership for Data folder to UnityFramework.

3.1. If you're using Swift, open the ios/Runner/AppDelegate.swift file and change the following:

     import UIKit
     import Flutter
+    import flutter_unity_widget

     @UIApplicationMain
     @objc class AppDelegate: FlutterAppDelegate {
         override func application(
             _ application: UIApplication,
             didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
         ) -> Bool {
+            InitUnityIntegrationWithOptions(argc: CommandLine.argc, argv: CommandLine.unsafeArgv, launchOptions)

             GeneratedPluginRegistrant.register(with: self)
             return super.application(application, didFinishLaunchingWithOptions: launchOptions)
         }
     }

3.2. If you're using Objective-C, open the ios/Runner/main.m file and change the following:

+    #import "flutter_unity_widget.swift.h"

     int main(int argc, char * argv[]) {
          @autoreleasepool {
+             InitUnityIntegration(argc, argv);
              return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
          }
     }

Add the UnityFramework.framework file as a library to the Runner project.

Unity plugins that make use of native code (Vuforia, openCV, etc.) might need to be added to Runner like UnityFramework.
Check the contents of the /ios/UnityLibrary/Frameworks/ directory. Any <name>.framework located in (subdirectories of) this directory is a framework that you can add to Runner.
Make sure pods are installed after your Unity export, either using flutter run or by running pod install in the ios folder.
If you use Xcode 14 or newer, and Unity older than 2021.3.17f1 or 2022.2.2f1, your app might crash when running from Xcode.
Disable the Thread Performance Checker feature in Xcode to fix this.
- In Xcode go to Product > Scheme > Edit Scheme...
- Now With Run selected on the left, got to the Diagnostics tab and uncheck the checkbox for Thread Performance Checker.

Setup AR

The following setup for AR is done after making an export from Unity.

Warning: Flutter 3.22 has introduced a crash when using AR on Android < 13 #957

ℹ️ AR Foundation Android

Check the version of the XR Plugin Management in the Unity package manager. Versions 4.3.1 - 4.3.3 contain a bug that breaks Android exports.
Make sure to use a version <=4.2.2 or >=4.4.
You might have to manually change the version in <unity project>/Packages/manifest.json for "com.unity.xr.management".
You can check the android/unityLibrary/libs folder to see if AR was properly exported. It should contain files similar to UnityARCore.aar, ARPresto.aar, arcore_client.aar and unityandroidpermissions.aar.

If your setup and export was done correctly, your project should automatically load these files.
If it doesn't, check if your android/build.gradle file contains the flatDir section added in the android setup step 7.
If your XR Plugin Management plugin is version 4.4 or higher, Unity also exports the xrmanifest.androidlib folder. Make sure to include it by adding the following line to android/settings.gradle
```
include ":unityLibrary:xrmanifest.androidlib"
```
With some Unity versions AR might crash at runtine with an error like:
java.lang.NoSuchFieldError: no "Ljava/lang/Object;" field "mUnityPlayer" in class.
See the Android setup step 3 on how to edit your MainActivity to fix this.

ℹ️ AR Foundation iOS

Open the ios/Runner/Info.plist and add a camera usage description.
For example:

     <dict>
+        <key>NSCameraUsageDescription</key>
+        <string>$(PRODUCT_NAME) uses Cameras</string>
     </dict>

ℹ️ Vuforia Android

Your export should contain a Vuforia library in the android/unityLibrary/libs/ folder. Currently named VuforiaEngine.aar.

If your setup and export was done correctly, your project should automatically load this file.
If it doesn't, check if your android/build.gradle file contains the flatDir section added in the android setup step 7.

In case this gets outdated or broken, check the Vuforia documentation

ℹ️ Vuforia iOS

These steps are based on these Vuforia docs and this comment

Open the ios/Runner/Info.plist and add a camera usage description.
For example:

     <dict>
+        <key>NSCameraUsageDescription</key>
+        <string>$(PRODUCT_NAME) uses Cameras</string>
     </dict>

In Xcode, Select Runner > General tab.
In Frameworks, Libraries, and Embedded content add the Vuforia frameworks. This is where you added UnityFramework.framework in step 4 of the iOS setup.

You should be able to find them in /ios/UnityLibrary/Frameworks/com.ptc.vuforia.engine/Vuforia/Plugins/iOS/.
Currently these are
- Vuforia.framework
- UnityDriver.framework
To support Vuforia target databases, move the Unity-iPhone/Vuforia folder from Unity-iPhone to Runner. Then set Target Membership of this folder to Runner.
Make sure pods are installed after your Unity export, either using flutter run or by running pod install in the ios folder.

Emulators

We recommend using a physical iOS or Android device, as emulator support is limited.
Below are the limited options to use an emulator.

iOS Simulators

The Target SDK option in the Unity player settings is important here.

Device SDK exports an ARM build. (Which does NOT work on ARM simulators)
Simulator SDK exports and x86 build for simulators.

If you use ARKit or ARFoundation you are out of luck, iOS simulators do NOT support ARKit.

The rest depends on the type of processor in your mac:

(Apple Silicon) Run it on mac directly

Export from Unity using Device SDK as target.
In Xcode, go to the General tab of Runner.
In Supported destinations add Mac (Designed for iPhone) or Mac (Designed for iPad).
Now select this as the target device to run on.
You can now run the app directly on your mac instead of a simulator.

(Intel & Apple Silicon) Use an x86 simulator

Set Simulator SDK in the Unity player settings.
Make sure there are no AR or XR packages included in the Unity package manager.
(You will get the error symbol not found in flat namespace '_UnityARKitXRPlugin_PluginLoad otherwise)
(Apple Silicon) Get Xcode to use a Rosetta emulator.
The next step assumes Xcode 14.3 or newer, if you use an older version look up how to start Xcode using Rosetta instead.

In Xcode go to Product -> Destination -> Destination Architectures and make sure Rosetta destinations are visible.

Now you need to check the architecture settings in Xcode.
Select Unity-iPhone and go to Build settings -> Architectures.
If you exported Unity with the Simulator SDK, it should show only x86_64 for architectures.
Now select Runner and change the architecture to exactly match Unity-iPhone.
Make sure x86_64 is the only entry, not one of multiple.
Now select Pods and click flutter_unity_widget in targets.
Go to Architectures in build settings again and set Build Active Architecture Only to YES.
(We want this to only use the active x86_64, not fall back to arm.)
Run Product -> Clean Build Folder to make sure the new architecture settings are used.
Now you should be able to launch Runner on a Simulator using Rosetta.
On Xcode 14.3 or higher the simulator should have (Rosetta) in the name.
Depending on your Flutter plugins, you might have to change the architecture for other installed Pods as well.

Android emulators

Unity only supports ARM build targets for Android. However most Android emulators are x86 which means they simply won't work.

Computer with ARM processor
If your computer has an ARM processor (e.g. Apple Silicon, Qualcomm) you should be able to emulate Android without issue.
Create a virtual device using Android studio and make sure that the system image has an ABI that includes 'arm'.

On macs with Apple Silicon (M1, M2), ARM emulators should be the default install option.

This was tested on Mac, but not on Linux or Windows.
Computer with x86/x64 processor
If you computer does not have an ARM processor, like most computers running on Intel or AMD, your options are limited.

You have 2 options:
- Download an ARM emulator from Android Studio anyway.
  While adding a virtual device in android studio, on the 'System image' screen, select 'other images' and make sure to use and ABI that includes 'arm'.
  The emulator will likely crash immediately or run extremely slow.
  This is not recommended.
- Use the Chrome OS architecture
  This is not officialy supported by Unity and there is no guarantee that it will work, but the Chrome OS target does seem to work on x86 Android emulators.
  Expect (visual) glitches and bugs
  - Enablex86 (Chrome OS) and x86-64 (Chrome OS) in the Unity player settings before making an export.
    You might now be able to run on an regular Android emulator.
  - Disable these settings again if you want to publish your app.

Communicating

Flutter-Unity

On a UnityWidget widget, get the UnityWidgetController received by the onUnityCreated callback.
Use the method postMessage to send a string, using the GameObject name and the name of a behaviour method that should be called.

Unity-Flutter

Select the GameObject that should execute the communication and go to Inspector > Add Component > Unity Message Manager.

Create a new MonoBehaviour subclass and add to the same GameObject as a script.
On this new behaviour, call GetComponent<UnityMessageManager>() to get a UnityMessageManager.
Use the method SendMessageToFlutter to send a string. Receive this message using the onUnityMessage callback of a UnityWidget.

Examples

Simple Example

import 'package:flutter/material.dart';
import 'package:flutter_unity_widget/flutter_unity_widget.dart';

void main() {
  runApp(
    const MaterialApp(
      home: UnityDemoScreen(),
    ),
  );
}

class UnityDemoScreen extends StatefulWidget {
  const UnityDemoScreen({Key? key}) : super(key: key);

  @override
  State<UnityDemoScreen> createState() => _UnityDemoScreenState();
}

class _UnityDemoScreenState extends State<UnityDemoScreen> {
  static final GlobalKey<ScaffoldState> _scaffoldKey =
      GlobalKey<ScaffoldState>();
  UnityWidgetController? _unityWidgetController;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: _scaffoldKey,
      body: SafeArea(
        bottom: false,
        child: WillPopScope(
          onWillPop: () async {
            // Pop the category page if Android back button is pressed.
            return true;
          },
          child: Container(
            color: Colors.yellow,
            child: UnityWidget(
              onUnityCreated: onUnityCreated,
            ),
          ),
        ),
      ),
    );
  }

  // Callback that connects the created controller to the unity controller
  void onUnityCreated(controller) {
    _unityWidgetController = controller;
  }
}

Communicating with and from Unity

import 'package:flutter/material.dart';
import 'package:flutter_unity_widget/flutter_unity_widget.dart';

void main() => runApp(const MyApp());

class MyApp extends StatefulWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  static final GlobalKey<ScaffoldState> _scaffoldKey =
      GlobalKey<ScaffoldState>();
  UnityWidgetController? _unityWidgetController;
  double _sliderValue = 0.0;

  @override
  void initState() {
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        key: _scaffoldKey,
        appBar: AppBar(
          title: const Text('Unity Flutter Demo'),
        ),
        body: Card(
          margin: const EdgeInsets.all(8),
          clipBehavior: Clip.antiAlias,
          shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(20.0),
          ),
          child: Stack(
            children: <Widget>[
              UnityWidget(
                onUnityCreated: onUnityCreated,
                onUnityMessage: onUnityMessage,
                onUnitySceneLoaded: onUnitySceneLoaded,
                fullscreen: false,
              ),
              Positioned(
                bottom: 20,
                left: 20,
                right: 20,
                // <You need a PointerInterceptor here on web>
                child: Card(
                  elevation: 10,
                  child: Column(
                    children: <Widget>[
                      const Padding(
                        padding: EdgeInsets.only(top: 20),
                        child: Text("Rotation speed:"),
                      ),
                      Slider(
                        onChanged: (value) {
                          setState(() {
                            _sliderValue = value;
                          });
                          setRotationSpeed(value.toString());
                        },
                        value: _sliderValue,
                        min: 0,
                        max: 20,
                      ),
                    ],
                  ),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }

  // Communcation from Flutter to Unity
  void setRotationSpeed(String speed) {
    _unityWidgetController?.postMessage(
      'Cube',
      'SetRotationSpeed',
      speed,
    );
  }

  // Communication from Unity to Flutter
  void onUnityMessage(message) {
    print('Received message from unity: ${message.toString()}');
  }

  // Callback that connects the created controller to the unity controller
  void onUnityCreated(controller) {
    _unityWidgetController = controller;
  }

  // Communication from Unity when new scene is loaded to Flutter
  void onUnitySceneLoaded(SceneLoaded? sceneInfo) {
    if (sceneInfo != null) {
      print('Received scene loaded from unity: ${sceneInfo.name}');
      print(
          'Received scene loaded from unity buildIndex: ${sceneInfo.buildIndex}');
    }
  }
}

Props

fullscreen (Enable or disable fullscreen mode on Android)

API

pause() (Use this to pause unity player)
resume() (Use this to resume unity player)
unload() (Use this to unload unity player) *Requires Unity 2019.4.3 or later
quit() (Use this to quit unity player)
postMessage(String gameObject, methodName, message) (Allows you invoke commands in Unity from flutter)
onUnityMessage(data) (Unity to flutter binding and listener)
onUnityUnloaded() (Unity to flutter listener when unity is unloaded)
onUnitySceneLoaded(String name, int buildIndex, bool isLoaded, bool isValid,) (Unity to flutter binding and listener when new scene is loaded)

Troubleshooting

Location: Unity

Error:

Multiple precompiled assemblies with the same name Newtonsoft.Json.dll included on the current platform. Only one assembly with the same name is allowed per platform. (Assets/FlutterUnityIntegration/JsonDotNet/Assemblies/AOT/Newtonsoft.Json.dll)

PrecompiledAssemblyException: Multiple precompiled assemblies with the same name Newtonsoft.Json.dll included on the current platform. Only one assembly with the same name is allowed per platform.

Solution: Locate the listed dll file, in this case: Assets/FlutterUnityIntegration/JsonDotNet/Assemblies/AOT/Newtonsoft.Json.dll

Option 1: Delete the dll file or rename the file extension (e.g. .dll.txt) to stop it from being imported.
Option 2: Uninstall the package that conflicts in the Unity package manager (usually Version control, or Collab). The exact package can be found by looking for newtonsoft in package-lock.json

Location: Unity

Error:

The type or namespace name 'Newtonsoft' could not be found (are you missing a using directive or an assembly reference?)
The type or namespace name 'JObject' could not be found (are you missing a using directive or an assembly reference?)
The type or namespace name 'JToken' could not be found (are you missing a using directive or an assembly reference?)
The type or namespace name 'JToken' could not be found (are you missing a using directive or an assembly reference?)

Solution:

Include the Newtonsoft JsonDotNet library. It is likely already included in your project with a wrong file extension: Assets/FlutterUnityIntegration/JsonDotNet/Assemblies/AOT/Newtonsoft.Json.dll.txt Rename the .dll.txt extension to .dll in your file explorer and open Unity again.

Alternatively you can manually add the library from the Unity package manager.

Location: Unity

Error:

InvalidOperationException: The build target does not support build appending.

Solution:

Open the unity/project-name/Assets/FlutterUnityIntegration/Editor/Build.cs file.

1.1. On line 48, change the following:

-    var options = BuildOptions.AcceptExternalModificationsToPlayer;
+    var options = BuildOptions.AllowDebugging;
+    EditorUserBuildSettings.exportAsGoogleAndroidProject = true;

1.2. On line 115, change the following:

-    var options = BuildOptions.AcceptExternalModificationsToPlayer;
+    var options = BuildOptions.AllowDebugging;

Location: Android Studio

Error:

minSdkVersion XX cannot be smaller than version 19 declared in library 
    \ [:flutter_unity_widget] .../AndroidManifest.xml as the library might be using 
    \ APIs not available in XX

Solution:

Open the android/app/build.gradle file and change the following:

-    minSdkVersion XX
+    minSdkVersion 19

Location: Android Studio

Error:

e: .../FlutterUnityWidgetBuilder.kt: (15, 42): Expecting a parameter declaration
e: .../FlutterUnityWidgetBuilder.kt: (23, 25): Expecting an argument
e: .../FlutterUnityWidgetController.kt: (22, 44): Expecting a parameter declaration
e: .../FlutterUnityWidgetFactory.kt: (13, 58): Expecting a parameter declaration

Solution:

Open the android/build.gradle file and change the following:

-    ext.kotlin_version = '1.3.50'
+    ext.kotlin_version = '1.4.31'

Location: Android Studio

Error:

Unable to find a matching variant of project :unityLibrary:

Solution:

Open the android/app/build.gradle file and change the following:

     lintOptions {
         disable 'InvalidPackage'
+        checkReleaseBuilds false
     }

Flavors

Recommendation

The easiest way to apply flavors for your app would be: flutter_flavorizr.

If you use flavors in your app you will notice that especially iOS crashes while running or building your app! Here are the necessary steps for flavored apps:

Android

No changes needed. Flavors are applied without any additional setups.

iOS

For your Unity iOS-Build you have to add your flavors to your Unity iOS Configuration.

Check your actual Runner (your app) configurations. If you have for example the flavors:

dev
prod

Your Runner configurations are looking like this:

So you have the flavors:

Debug-dev
Profile-dev
Release-dev
Debug-prod
Profile-prod
Release-prod

These flavors needs to be added to your Unity-IPhone project.

Go into your Unity-IPhone project -> PROJECT Unity-IPhone -> Info:

Here you can see in the Configurations section only:

Release
ReleaseForProfiling
ReleaseForRunning
Debug

Copy Debug configuration twice and rename them to Debug-dev and the second to Debug-prod.

You can do that by selecting + and duplicate the configuration like this:

Repeat this with Release to Release-dev and Release-prod.
Repeat this with Release to Profile-dev and Profile-prod.
Your Unity-IPhone configurations should now look like this:

Web

Flutter on default doesn't support --flavor for building web. But you can set your target main.dart entrypoint (with -t main.dart) while running and building. So if you setup your flavors properly there're also no changes needed for web to apply changes for your Flutter-Unity web App.

Known issues

Remember to disabled fullscreen in unity player settings to disable unity fullscreen.
Unity freezes and crashes on Android, please use OpenGL3 as Graphics API.
Project fails to build due to some native dependencies in your unity project, please integrate the native libraries for those dependencies on Android or iOS
App crashes on screen exit and re-entry do this

Build Setting - iOS - Other Settings - Configuration - Enable Custom Background Behaviors or iOS
Android builds takes forever to complete Unity 2022.1.*, remove these lines from unityLibrary/build.gradle file

commandLineArgs.add("--enable-debugger") commandLineArgs.add("--profiler-report") commandLineArgs.add("--profiler-output-file=" + workingDir + "/build/il2cpp_"+ abi + "_" + configuration + "/il2cpp_conv.traceevents")

Web GL

Flutter widgets stacked on top of the UnityWidget will not register clicks or taps. This is a Flutter issue and can be solved by using the PointerInterceptor package.

Example usage:

Stack(
  children: [
    UnityWidget(
      onUnityCreated: onUnityCreated,
      onUnityMessage: onUnityMessage,
      onUnitySceneLoaded: onUnitySceneLoaded,
    ),
    Positioned(
      bottom: 20,
      left: 20,
      right: 20,
      child: PointerInterceptor(
        child: ElevatedButton(
          onPressed: () {
            // do something
          },
          child: const Text('Example button'),
        ),
      ),
    ),