How to sign out from Google authentication in another Fragment?

Question

I am logging in with Google authentication. It will start an intent to another Java. In this Fragment I have a Sign out-button, but every time I want to sign out, the app crashes. Can you guys help me? :)

The Error message I am getting is:

java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context com.google.android.gms.common.api.GoogleApiClient.getContext()' on a null object reference

Code:

public class Setttings extends Activity {

private Button msigno;
private FirebaseAuth mAuth;

private GoogleApiClient mGoogleApiClient;

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.settings);


    DisplayMetrics dm = new DisplayMetrics();
    getWindowManager().getDefaultDisplay().getMetrics(dm);

    int width = dm.widthPixels;
    int height = dm.widthPixels;

    getWindow().setLayout((int)(width*0.95),(int) (height*0.93));

    msigno = (Button) findViewById(R.id.signout);

    msigno.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            mAuth = FirebaseAuth.getInstance();

            switch (v.getId()) {
                // ...
                case R.id.signout:
                    signOut();
                    break;
                // ...

            }
            mAuth.signOut();

            // Google sign out
            Auth.GoogleSignInApi.signOut(mGoogleApiClient).setResultCallback(
                    new ResultCallback<Status>() {
                        @Override
                        public void onResult(@NonNull Status status) {
                        }
                    });
            Intent intent2 = new Intent(Setttings.this, MainActivity.class);
            startActivity(intent2);

        }
    });



}
private void signOut() {
    Auth.GoogleSignInApi.signOut(mGoogleApiClient).setResultCallback(
            new ResultCallback<Status>() {
                @Override
                public void onResult(Status status) {
                    // ...
                }
            });
}
}

Answer 1

需要初始化API客户端才能退出。

@Override
protected void onStart() {
    GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
            .requestEmail()
            .build();
    mGoogleApiClient = new GoogleApiClient.Builder(this)
            .addApi(Auth.GOOGLE_SIGN_IN_API, gso)
            .build();
    mGoogleApiClient.connect();
    super.onStart();
}