How to get activity context in ViewModel Android?

Question

I am using MVVM. I want to implement Firebase Auth in app. But to implement it I need an activity context in my repo class. How can I get it from ViewModel or is there any simple method available?

Here is the firebase code I need to implement:

 PhoneAuthProvider.getInstance().verifyPhoneNumber("+91"+phone,        // Phone number to verify
            60,                 // Timeout duration
            TimeUnit.SECONDS,   // Unit of timeout
            (Activity) context,               // Activity (for callback binding)
            new PhoneAuthProvider.OnVerificationStateChangedCallbacks() {
                @Override
                public void onVerificationCompleted(@NonNull PhoneAuthCredential phoneAuthCredential) 
               {
                    signInWithPhoneAuthCredential((Activity)context,phoneAuthCredential);
                }

                @Override
                public void onVerificationFailed(@NonNull FirebaseException e) {
                    setLoginFailed(e);

                }

                @Override
                public void onCodeSent(@NonNull String s, @NonNull 
                PhoneAuthProvider.ForceResendingToken forceResendingToken) {
                    super.onCodeSent(s, forceResendingToken);
                    loginResponse.setOnProgress(false);
                    loginResponse.setStatus(true);
                    loginResponse.setCodeVerified(false);
                    loginResponseLiveData.setValue(loginResponse);
                    verificationId =s;

                }
            });

Answer 1

In general, ViewModel objects are not supposed to reference anything that has to do with the Android platform APIs, especially Activity objects. You would not want a ViewModel to retain (and leak) an Activity across orientation changes. Retaining Activity objects in a ViewModel is a huge anti-pattern that should be avoided.

Instead, you should use a different version of that Firebase API. Choose one of the alternatives that do not take an Activity, according to the API documentation. Once the API is complete, you can bubble a callback up to the hosting activity to start any other activities.

Answer 2

First of all, according to official view model guidelines:

Caution: A ViewModel must never reference a view, Lifecycle, or any class that may hold a reference to the activity content

So in accordance with your MVVM architecture, don't pass your activity context to a ViewModel.

I guess in that method you want to implement you do not specifically need an activity context. You could also use the context of your application.

Follow these 3 steps of this answer to get access your Application context statically:

1. create Application class which references the context on create

   public class MyApplication extends Application {
   
       private static Context context;
   
       public void onCreate() {
           super.onCreate();
           MyApplication.context = getApplicationContext();
       }
   
       public static Context getAppContext() {
           return MyApplication.context;
       }
   }
   

2. Declare your application class in your Manifest

   <application android:name="com.xyz.MyApplication">
   
   </application>
   

3. Access this context statically inside your repository class

   MyApplication.getAppContext()
   

There is also the possibility to access the application context via AndroidViewModel class. But I guess you usually do not want to initialize your repository from your ViewModel.