Q:

java.lang. NoClassDefFoundError: Failed resolution of: Landroidx/arch/core/util/Cancellable

I split my app project into other modules and after implementing DI and splitting the dependencies across the modules, I get this exception:
java.lang. NoClassDefFoundError: Failed resolution of: Landroidx/arch/core/util/Cancellable;
        at androidx.activity. ComponentActivity.<init>(ComponentActivity.java:69)
        at androidx.fragment.app. FragmentActivity.<init>(FragmentActivity.java:118)
        at androidx.appcompat.app. AppCompatActivity.<init>(AppCompatActivity.java:77)

Then, I check the ComponentActivity class and, yes, said class can´t find the Cancellableclass. 
package androidx.activity;  

import static android.os. Build. VERSION.SDK_INT;  

import android.os. Build;  
import android.os. Bundle;  
import android.view. View;  
import android.view. Window;  

import androidx.annotation. CallSuper;  
import androidx.annotation. ContentView;  
import androidx.annotation. LayoutRes;  
import androidx.annotation. NonNull;  
import androidx.annotation. Nullable;  
import androidx.arch.core.util. Cancellable; // <---- This class can't be found! 
import androidx.lifecycle. GenericLifecycleObserver;  
import androidx.lifecycle. Lifecycle;  
import androidx.lifecycle. LifecycleOwner;  
import androidx.lifecycle. LifecycleRegistry;  
import androidx.lifecycle. ReportFragment;  
import androidx.lifecycle. ViewModelStore;  
import androidx.lifecycle. ViewModelStoreOwner;  
import androidx.savedstate. SavedStateRegistry;  
import androidx.savedstate. SavedStateRegistryController;  
import androidx.savedstate. SavedStateRegistryOwner;  

import java.util. WeakHashMap;  

/**  
 * Base class for activities that enables composition of higher level components. *  <p>  
  * Rather than all functionality being built directly into this class, only the minimal set of  
 * lower level building blocks are included.  Higher level components can then be used as needed * without enforcing a deep Activity class hierarchy or strong coupling between components. * /public class ComponentActivity extends androidx.core.app. ComponentActivity implements  
  LifecycleOwner,  
  ViewModelStoreOwner,  
  SavedStateRegistryOwner {

After taking a look at the package, I decided to add this dependency:
implementation "androidx.core:core:1.1.0-alpha05"
yet, it still fails. 
Then I checked some questions here in StackOverflow that recommended use Multidex, so, I enabled mutlidex in my build.gradlefile but yet, it still fails
I added Multidex like this:
implementation "androidx.multidex:multidex:2.0.0"
build.gradle
defaultConfig {  
// Config stuff
  multiDexEnabled = true  
}

and making my Application class extend the MultiDexApplication class, yet, it still fails
Seems like im missing a dependency here, but I can't find it. : c

A:

As per the androidx.arch.core release notes:

The Cancellable interface has been deprecated due to a lack of composable infrastructure and its removal from public API in androidx.activity 1.0.0-alpha07. ( aosp/945461)

Therefore you should upgrade to Activity 1.0.0-alpha07 or higher to remove ComponentActivity's dependency on Cancellable.  This is automatically done when you upgrade to Fragments 1.1.0-alpha07 or higher.