Default interface methods are only supported starting with Android 7.0 (Nougat)

Question

I upgraded to Android Studio 3.1 and I'm getting the following error:

Default interface methods are only supported starting with Android N (--min-api 24): void android.arch.lifecycle.DefaultLifecycleObserver.onCreate(android.arch.lifecycle.LifecycleOwner)

Message{kind=ERROR, text=Default interface methods are only supported starting with Android N (--min-api 24): void android.arch.lifecycle.DefaultLifecycleObserver.onCreate(android.arch.lifecycle.LifecycleOwner), sources=[Unknown source file], tool name=Optional.of(D8)}

Here is my Gradle configuration:

compileSdkVersion 27 //buildToolsVersion '27.0.3' defaultConfig {     minSdkVersion 16     targetSdkVersion 27      multiDexEnabled true      //...    } 

As you can see, I am targeting 27 which is already ahead of 24 that it's complaining about. What exactly should I do to fix this? If I change to 1.8 Java, won't I be missing a lot of customers? Why was I not getting this error before I upgraded Android Studio?

I do not know if this is about the LifecycleObserver class I recently put in. It was in Kotlin and now I changed it to Java, but I still get the same error after cleaning the project:

public class LifeCycleAwareObserver implements LifecycleObserver {      @OnLifecycleEvent(Lifecycle.Event.ON_STOP)     public void  onAppBackgrounded() {         AnalyticsUtils.trackStartSession(true);     }      @OnLifecycleEvent(Lifecycle.Event.ON_START)     public void onAppForegrounded() {         AnalyticsUtils.trackStartSession(false);     } } 

How can I trace where the error is coming from so I can fix it?

Here are my version dependencies:

project.ext {          firebase_version = '12.0.0'          supportlib_version = '27.0.2'          room_version = '1.0.0'          espresso_version = '3.0.1'          archLifecycleVersion = '1.1.1'     } 

Answer 1

As CommonsWare mentioned, for reference add this inside the android {...} closure in the build.gradle for your app module (app level) to resolve the issue:

android { ...   compileOptions {         sourceCompatibility JavaVersion.VERSION_1_8         targetCompatibility JavaVersion.VERSION_1_8     } ... } 

Answer 2

You should use Java 8 to solve this. Based on the Android documentation, you can do this by clicking menu File → Project Structure.

And change Source Compatibility and Target Compatibility.

And you can also configure it directly in the app-level build.gradle file:

android {   ...   // Configure only for each module that uses Java 8   // language features (either in its source code or   // through dependencies).   compileOptions {     sourceCompatibility JavaVersion.VERSION_1_8     targetCompatibility JavaVersion.VERSION_1_8   } }