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;

                }
            });

score 1 · Answer 1 · answered Sep 06 '20 at 06:58

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.

answered Sep 06 '20 at 06:58

Doug Stevenson

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yes, I was also thinking that I am violating the law of MVVM...i didn't find an alternative inAPI doc.. so I should handle it in activity!!? – sum20156 Sep 06 '20 at 07:44
In my answer, I linked to API documentation that gives you multiple alternatives of `verifyPhoneNumber` that do not use an Activity. I'm recommending that you use one of those altenratives. – Doug Stevenson Sep 06 '20 at 15:52

score 1 · Answer 2 · edited Sep 06 '20 at 08:47

1

If you work not related to any UI then you can use AndroidViewModel instead of ViewModel
In AndroidViewModel there in one important default parameter ApplicationContext
Or if you want any specific activity References then use LiveData<YourActivity> and set class reference when you initialize ViewModel in class

edited Sep 06 '20 at 08:47

Peter Haddad

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answered Sep 06 '20 at 07:03

Vikas

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i can't use android view model as I need activity context for firebase.. can you briefly explain LiveData thing – sum20156 Sep 06 '20 at 07:41
OK in you View Model Class Add This first var activityReference: MutableLiveData? = MutableLiveData() and in your Activity Class add This line viewModel.activityReference?.value = this@SignUpActivity //(your class reference) then in your view model you have reference of your current activity – Vikas Sep 06 '20 at 07:46
What is `AndroidViewModel`? How to use that. – IgorGanapolsky Apr 22 '21 at 01:39

cewaphi · Answer 3 · 2020-09-06T07:10:20.257

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:

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;
    }
}

Declare your application class in your Manifest

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

</application>

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.

storing context like this may result in memory leak..also I have already tried using AndroidViewModel but as you know it provides application context, not activity context... so firebase giving exception..and ask to cast the context from application to activity — sum20156, Sep 06 '20 at 07:39
Then what about Doug Stevenson's suggestion, does the API also provide such a method without requiring the activity context? It would probably be the best solution if you do not need to worry about messing with the context at all — cewaphi, Sep 06 '20 at 07:44

How to get activity context in ViewModel Android?

3 Answers3