Flutter Gradle should automatically add MultiDex

[slightfoot]

Steps to Reproduce

Build app with more than 64K methods.

Logs

The number of method references in a .dex file cannot exceed 64K.
Learn how to resolve this issue at https://developer.android.com/tools/building/multidex.html

Recommended Changes

1. Project template or flutter.gradle script should set the multiDexEnabled property to true, and add the multiDexKeepFile file('multidex-flutter.txt') config file. Example: multidex-flutter.txt

   io/flutter/app/FlutterApplication.class
   io/flutter/view/FlutterMain.class
   io/flutter/util/PathUtils.class
   

2. Project template or flutter.gradle script should add the multidex dependency.
   implementation 'com.android.support:multidex:1.0.3'

3. FlutterApplication should have the following addition.

   @Override
   protected void attachBaseContext(Context base)
   {
       super.attachBaseContext(base);
       MultiDex.install(this);
   }

Adding the multiDexKeepFile is important as the FlutterApplication class and its dependencies are required to me in the primary dex file or the Application class may its onCreate lifecycle event.

Flutter 0.5.7 • channel v0.5.7 • https://github.com/slightfoot/flutter
Framework • revision 66091f9696 (7 weeks ago) • 2018-07-09 12:52:41 -0700
Engine • revision 6fe748490d
Tools • Dart 2.0.0-dev.63.0.flutter-4c9689c1d2

[slightfoot]

Was just caught by this. @Hixie @eseidel I think this is important addition towards v1.0, especially when we have lots of users that have no previous app-dev experience, and its a big gotcha.

[BugsBunnyBR]

While multidex is important, it should not be the default option. It makes the app loading and compiling time longer.
I think it should be an opt-in feature. Maybe flutter cli could update the project structure to solve this when the developer requests to.

[slightfoot]

@BugsBunnyBR I believe the compilation time is not as big of a deal, as it once was. Remember instant-run, and other tooling use multiple dex files and use adb install-multiple. The tooling has vastly improved since multidex's initial launch. Compilation time is a problem in the "Android" world, but because of hot-reload and hot-restart it's not so much of an issue when it comes to Flutter development. Yes, app-loading takes a hit to load multiple dex files, but that's only when there are more than one dex file, and only on pre-v21 since multi-dex is a no-op on v21+ because the framework loads multiple dex files now.

I think as long as it is handled by the Flutter framework and not left to the developer to figure out the black magic then I'm all happy for either, fixed or a opt-in feature, like a extra parameter on the create command, and/or a tick-box in the IntelliJ plugin.

Either way, along as something is done, I'm happy.

[Hixie]

cc @matthew-carroll @jason-simmons @filiph

[Hixie]

cc @bparrishMines

[Hixie]

cc @gspencergoog

[Hixie]

Maybe we should trigger this automatically when we hit the limit? (You're likely to hit the limit with some of our plugins.)

[matthew-carroll]

Seems reasonable to support. I agree with the earlier comment that it should not be enabled by default. We might consider exposing this via pubspec for ephemeral projects. Once the host app is made editable, it's up to the developer to deal with this, I think.

[slightfoot]

I just upgraded to Android Studio 3.2.0 and saw this in the notes:

Native multi-dex enabled by default: The Android plugin for Gradle now enables native multidex for all modules that set minSdkVersion = 21 or higher.

This might have an effect on this ticket.

[gspencergoog]

That's great, and it helps, but I don't think it has too much effect here, because Flutter supports API Level 16 and above, so we still have to do something about API levels 16-20.

[filiph]

Correct. Just setting minSdkVersion = 21 in build.gradle makes the multidex issue go away. But Flutter has minSdkVersion set to 16 by default, and it's one of the selling points of the SDK.

[slightfoot]

My earlier remark was not to set the minSdk, but rather to be aware of the build change, just in case the app developer changes the minSdk to 21 or above and screws up the possible fix for this ticket.

[slightfoot]

Either way you always going to need the multiDexKeepFile or some of the initialisation files might go in classes2.dex or something and the app fails to load.

[raveesh-me]

Maybe we should trigger this automatically when we hit the limit? (You're likely to hit the limit with some of our plugins.)

This would be amazing...

[drexel-ue]

I've just run into the same issue trying to build

D8: Cannot fit requested classes in a single dex file (# methods: 85866 > 65536)

attempting the fix now

[robert-stevens]

@drexel-ue i've just run into it now, do you have any fix?

[slightfoot]

Enable Multidex as described here, and adjust it with my instructions in the description of the ticket.
https://developer.android.com/studio/build/multidex

If that doesn't work, today is Wednesday which is Flutter #HumpDayQandA and you can join us on Zoom to chat about the issue and resolve it. https://tinyurl.com/HumpDayQandA

[Leisser]

Am new to flutter and also to app-dev but not sure how i must treat this code

@Override protected void attachBaseContext(Context base) { super.attachBaseContext(base); MultiDex.install(this); }

in my flutter application, am i supposed to put it in my main.dart. Am too confused.

I've edited my app/build.gradle script and enabled multiDexEnabled, added implementation 'com.android.support:multidex:1.0.3' and multiDexKeepFile file('multidex-flutter.txt').
The app crashes on after installation, thought am only missing the override bit but don't know how to handle it.

[wtoalabi]

Am new to flutter and also to app-dev but not sure how i must treat this code

@Override protected void attachBaseContext(Context base) { super.attachBaseContext(base); MultiDex.install(this); }

in my flutter application, am i supposed to put it in my main.dart. Am too confused.

I've edited my app/build.gradle script and enabled multiDexEnabled, added implementation 'com.android.support:multidex:1.0.3' and multiDexKeepFile file('multidex-flutter.txt').
The app crashes on after installation, thought am only missing the override bit but don't know how to handle it.

I am seriously looking for a solution to this.
I found this: https://stackoverflow.com/questions/53740908/flutter-enable-multidex-for-sdk-less-than-21
But just like you, no way to know where to put that snippet of code.

[slightfoot]

For those that are having problems.. follow these instructions.

1. Open Android Studio and choose "Open and existing Android Studio project" and choose the android directory inside your project directory.

2. Wait for gradle to sync.

3. In the project explorer panel on the left open the app/java folder and keep expanding down until you find MainActivity.java then right click on the parent folder and choose New > Java Class. Name the new class appropriately for your app. I'll use ExampleApp. (do not actually use this name)

4. In the new ExampleApp.java file edit your class to extend from FlutterApplication, and override attachBaseContext the result should look similar to below, save it.

   package com.example.mobile;
   
   import android.content.Context;
   
   import android.support.multidex.MultiDex;
   import io.flutter.app.FlutterApplication;
   
   
   public class ExampleApp extends FlutterApplication
   {
       @Override
       protected void attachBaseContext(Context base)
       {
           super.attachBaseContext(base);
           MultiDex.install(this);
       }
   }
   

   If you have any red errors or issues. Open your app modules build.gradle script and add this line to your dependencies section and run gradle sync again.
   compileOnly files("$flutterRoot/bin/cache/artifacts/engine/android-x64/flutter.jar")

5. Now expand the manifests section in your project explorer and open AndroidManifest.xml. Find the <application> tag delete the contents of the android:name attribute and replace it with .ExampleApp (the name of your class from the previous step).

Those instructions show you how to create a android Application class and attach MultiDex support library to it. More info can be found here: https://developer.android.com/studio/build/multidex

Don't forget you'll need to add multiDexEnabled true and multiDexKeepFile file('multidex-flutter.txt') to your defaultConfig in your build.gradle file. Place the multidex-flutter.txt in your android\app folder. Example: multidex-flutter.txt

io/flutter/app/FlutterApplication.class
io/flutter/view/FlutterMain.class
io/flutter/util/PathUtils.class

Side Note: If you upgrade your Android project to use AndroidX then you'll need to change the dependency from com.android.support:multidex:1.0.3 to androidx.multidex:multidex:2.0.0 and replace android.support.multidex.MultiDex with androidx.multidex.MultiDex. Migration details here: https://developer.android.com/jetpack/androidx/migrate

[wtoalabi]

Very detailed.
Thanks so much!
Here are my issues...Note that this is a fresh flutter installation with only a handful official plugins installed for firebase.

Following your instructions, here are my observations and where i'm stuck:

1. In the newly created java class file, this line:
   import android.support.multidex.MultiDex;
   shows "Cannot resolve symbol "MultiDex"

2. I think this has to do with the error you warned about, so I added:
   compileOnly files("$flutterRoot/bin/cache/artifacts/engine/android-x64/flutter.jar")
   to my gradle.build dependencies.
   However, I cant see where to "sync gradle again" as you advised.
   And also, I am not sure if "$flutterRoot" should be passed in raw as it is, or if I should change that string to the directory of my flutter sdk.

I dont feel comfortable going further with the rest of the instructions until I am able to sort these 2 out.
Thanks so much for your help!

[slightfoot]

You need to have implementation 'com.android.support:multidex:1.0.3' in your app module dependencies section.

[wtoalabi]

Apologies if I am sounding so dumb....I cant see where to sync gradle.
I have added the line as suggested, yet the Cannot resolve symbol MultiDex still shows.
I am on the latest Android Studio (3.3.1)

[wtoalabi]

So, I realise I cant beat the 64k limit, at least not with my constraints (below 20SDKs are a must). I eventually settled with adding Proguard to the debug section of my buildTypes (within the project level build.gradle file).
The result was the same, as I got over 43,000 methods scrapped, to give me just a little above 27,000 methods.
And now, I get to test and debug my app on low SDK phones without hitting the limits as Proguards does amazing job of scrapping off unused methods.
Shout out to @slightfoot for helping me out...even via screen sharing sessions.
I am grateful!

[Leisser]

@slightfoot thanks for the help am humbled.