Android Studio - findViewById() causing error

Question

This is my first post so apologies if I get any of the formalities wrong...

Before anyone tells me the question is invalid, every solution I have looked at says I should have:

setContentView(R.layout.whateverViewImCurrentlyTryingToFocus)

before I call a

findViewById()

When I debug my application it is crashing when I set up an onClickListener for my button (R.id.sign_in_button), line 75.

So I decided to check what findViewById() was returning so I run the code

Button button = findViewById(R.id.sign_in_button)

This caused the same error. I think it it returning null but not entirely sure.

Activitylogin.xml is the first layout to be loaded, and then the mainactivity.xml is supposed to launch after a firebase sign-in.

Java code:

LoginActivity.java

package com.styryl.socials.ui.login;

import android.app.Activity;

import androidx.annotation.NonNull;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;

import android.content.Intent;
import android.os.Bundle;

import androidx.annotation.Nullable;
import androidx.annotation.StringRes;
import androidx.appcompat.app.AppCompatActivity;

import android.text.Editable;
import android.text.TextWatcher;
import android.util.Log;
import android.view.KeyEvent;
import android.view.View;
import android.view.inputmethod.EditorInfo;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

import com.google.android.gms.auth.api.signin.GoogleSignIn;
import com.google.android.gms.auth.api.signin.GoogleSignInAccount;
import com.google.android.gms.auth.api.signin.GoogleSignInClient;
import com.google.android.gms.auth.api.signin.GoogleSignInOptions;
import com.google.android.gms.common.api.ApiException;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.android.material.snackbar.Snackbar;
import com.google.firebase.auth.AuthCredential;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.auth.GoogleAuthProvider;
import com.styryl.socials.MainActivity;
import com.styryl.socials.R;
import com.styryl.socials.ui.login.LoginViewModel;
import com.styryl.socials.ui.login.LoginViewModelFactory;

public class LoginActivity extends AppCompatActivity {

    private LoginViewModel loginViewModel;
    private FirebaseAuth mAuth;
    private GoogleSignInClient mGoogleSignInClient;
    private final static int RC_SIGN_IN = 1;
    private String TAG = "Login Activity";

    @Override
    protected void onStart() {
        super.onStart();

        FirebaseUser user = mAuth.getCurrentUser();

        if(user != null){
            Intent intent = new Intent(getApplicationContext(), MainActivity.class);
            startActivity(intent);
        }
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
        mAuth = FirebaseAuth.getInstance();

        createRequest();

        // Button findViewByID returns null
        findViewById(R.id.sign_in_button).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                signIn();
            }
        });
        }

    private void createRequest() {
        // Configure Google Sign In
        GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestIdToken(getString(R.string.default_web_client_id))
                .requestEmail()
                .build();

        // Build a GoogleSignInClient with the options specified by gso.
        mGoogleSignInClient = GoogleSignIn.getClient(this, gso);
    }

    private void signIn() {
        Intent signInIntent = mGoogleSignInClient.getSignInIntent();
        startActivityForResult(signInIntent, RC_SIGN_IN);
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        // Result returned from launching the Intent from GoogleSignInApi.getSignInIntent(...);
        if (requestCode == RC_SIGN_IN) {
            Task<GoogleSignInAccount> task = GoogleSignIn.getSignedInAccountFromIntent(data);
            try {
                // Google Sign In was successful, authenticate with Firebase
                GoogleSignInAccount account = task.getResult(ApiException.class);
                Log.d(TAG, "firebaseAuthWithGoogle:" + account.getId());
                firebaseAuthWithGoogle(account.getIdToken());
            } catch (ApiException e) {
                // Google Sign In failed, update UI appropriately
                Log.w(TAG, "Google sign in failed", e);
                Toast.makeText(this, e.getMessage(), Toast.LENGTH_SHORT).show();
                // ...
            }
        }
    }

    private void firebaseAuthWithGoogle(String idToken) {
        AuthCredential credential = GoogleAuthProvider.getCredential(idToken, null);
        mAuth.signInWithCredential(credential)
                .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        if (task.isSuccessful()) {
                            // Sign in success, update UI with the signed-in user's information
                            Log.d(TAG, "signInWithCredential:success");
                            FirebaseUser user = mAuth.getCurrentUser();
                            Intent intent = new Intent(getApplicationContext(), MainActivity.class);
                            startActivity(intent);
                        } else {
                            // If sign in fails, display a message to the user.
                            Log.w(TAG, "signInWithCredential:failure", task.getException());
                            Toast.makeText(LoginActivity.this, "Authentication Failed.", Toast.LENGTH_SHORT).show();
                        }
                    }
                });
    }
}

MainActivity.java

package com.styryl.socials;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import com.google.android.gms.auth.api.signin.GoogleSignIn;
import com.google.android.gms.auth.api.signin.GoogleSignInAccount;
import com.google.android.material.bottomnavigation.BottomNavigationView;
import com.google.firebase.auth.FirebaseAuth;
import com.styryl.socials.ui.login.LoginActivity;

import androidx.appcompat.app.AppCompatActivity;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.AppBarConfiguration;
import androidx.navigation.ui.NavigationUI;

public class MainActivity extends AppCompatActivity {

    TextView user_username;
    TextView user_email;

    Button logout;


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

        user_username = findViewById(R.id.user_username);
        user_email = findViewById(R.id.user_email);
        logout = findViewById(R.id.logout_button);

        BottomNavigationView navView = findViewById(R.id.nav_view);
        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        AppBarConfiguration appBarConfiguration = new AppBarConfiguration.Builder(
                R.id.navigation_home, R.id.navigation_dashboard, R.id.navigation_profile)
                .build();
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);
        NavigationUI.setupWithNavController(navView, navController);

        GoogleSignInAccount signInAccount = GoogleSignIn.getLastSignedInAccount(this);
        if(signInAccount != null){
            user_username.setText(signInAccount.getDisplayName());
            user_email.setText(signInAccount.getEmail());
        }

        logout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FirebaseAuth.getInstance().signOut();
                Intent intent = new Intent(getApplicationContext(), LoginActivity.class);
                startActivity(intent);
            }
        });
    }

}

Layout Files:

LoginActivity.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".ui.login.LoginActivity">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
        <TextView
            android:id="@+id/status_textview"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="" />
        <com.google.android.gms.common.SignInButton
            android:id="@+id/sign_in_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
        <Button
            android:layout_width="110dp"
            android:layout_height="wrap_content"
            android:text="Sign Out"
            android:id="@+id/sign_out_button" />
    </LinearLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorDarkGrey"
    android:paddingTop="?attr/actionBarSize">

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/nav_view"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:background="@color/colorPrimaryDark"
        app:itemIconTint="@drawable/bottom_navigation_selector"
        app:itemTextColor="@drawable/bottom_navigation_selector"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:menu="@menu/bottom_nav_menu" />

    <fragment
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/colorPrimaryDark"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toTopOf="@id/nav_view"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/mobile_navigation" />

</androidx.constraintlayout.widget.ConstraintLayout>

If you need anymore information please let me know and I will provide. I can't wrap my head around this issue and really hope some android studio experts can explain it to me as if I'm a idiot because I would love to learn!

I am attempting to fix this as soon as I wake up, because I never quit!

If your app crashes there will be an error message in its logcat output. Please find both and copy/paste them into your question (there's a handy edit link right under it). — Frank van Puffelen, May 31 '20 at 03:38
When you run ```Button button = findViewById(R.id.sign_in_button)```, it might not be a NullPointerException. Class SignInButton doesn't inherit from Button but inherits from FrameLayout. https://developers.google.com/android/reference/com/google/android/gms/common/SignInButton I think it occured error due to casting problem. — , May 31 '20 at 03:48
@Reece Draper try casting like this to see if it works. `((com.google.android.gms.common.SignInButton)findViewById(R.id.sign_in_button)).setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { signIn(); } }); }` — cgb_pandey, May 31 '20 at 04:04
The stack trace is needed to solve this problem. This is NOT casting problem and it is being occured by another reason. — , May 31 '20 at 08:24

score 0 · Accepted Answer · answered May 31 '20 at 08:26

All,

Thank you for your replies,

I woke up this morning and after looking at the logcat as suggested by @Frank van puffelen, I noticed that the error was a nullPointerException on a textView. This was weird becuase there was no textView in my loginActivity. Upon further inspection, I hadn't created the username and the email textView in my main_activity.xml (Problem with late night coding, I should have spotted that). So this was returning a nullPointerException simply because it didn't exist. I added the username, email and logout button to the xml and it works.

Thanks for the help, not entirely sure how to close this thread (this is my first post), apologies for wasting time but I was a little desperate.

Android Studio - findViewById() causing error

1 Answers1