How to Enable multidex for Flutter apps with over 64K methods

About the 64K reference limit

Android app (APK) files contain executable bytecode files in the form of Dalvik Executable (DEX) files, which contain the compiled code used to run your app. The Dalvik Executable specification limits the total number of methods that can be referenced within a single DEX file to 65,536—including Android framework methods, library methods, and methods in your own code. In the context of computer science, the term Kilo, K, denotes 1024 (or 2^10). Because 65,536 is equal to 64 X 1024, this limit is referred to as the ’64K reference limit’.

Configure your app for multidex

If your minSdkVersion is set to 21 or higher, multidex is enabled by default and you do not need the multidex library.

However, if your minSdkVersion is set to 20 or lower, then you must use the multidex library and make the following modifications to your app project:

Modify the module-level android >> app >>build.gradle file to enable multidex and add the multidex library as a dependency, as shown here:

android {
    defaultConfig {
        ...
        minSdk = 15 
        targetSdk = 28
        multiDexEnabled = true
    }
    ...
}

dependencies {
    implementation("androidx.multidex:multidex:2.0.1")
}

Avoid the 64K limit

Before configuring your app to enable use of 64K or more method references, you should take steps to reduce the total number of references called by your app code, including methods defined by your app code or included libraries. The following strategies can help you avoid hitting the DEX reference limit:

• Review your app’s direct and transitive dependencies – Ensure any large library dependency you include in your app is used in a manner that outweighs the amount of code being added to the app. A common anti-pattern is to include a very large library because a few utility methods were useful. Reducing your app code dependencies can often help you avoid the DEX reference limit.
• Remove unused code with R8 – Enable code shrinking to run R8 for your release builds. Enabling shrinking ensures you are not shipping unused code with your APKs.

Using these techniques might help you avoid the need to enable multidex in your app while also decreasing the overall size of your APK.

Reference:
https://developer.android.com/studio/build/multidex#kts