Firebase Auth causing Fatal exeception: (java.lang.NullPointerException)

Issue

This worked perfectly fine from the time I created the project. But suddenly is starts crashing. The sign up activity works fine. But this sign in activity is crashing.

The error shown by the debugger.

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.durden, PID: 7921
    java.lang.NullPointerException
        at com.example.durden.activity.SignInActivity.onCreate$lambda-2(SignInActivity.kt:49)
        at com.example.durden.activity.SignInActivity.$r8$lambda$ZBrxDCm4vr69l-PuE690AA_KCF8(Unknown Source:0)
        at com.example.durden.activity.SignInActivity$$ExternalSyntheticLambda1.onClick(Unknown Source:4)
        at android.view.View.performClick(View.java:7125)
        at android.view.View.performClickInternal(View.java:7102)
        at android.view.View.access$3500(View.java:801)
        at android.view.View$PerformClick.run(View.java:27336)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

The signin Activity

class SignInActivity : AppCompatActivity() {

    // getting the references from firebase
    private var auth: FirebaseAuth? = null
    private var firebaseUser: FirebaseUser? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        // gets the view binding of sign_in_activity
        val binding = ActivitySignInBinding.inflate(layoutInflater)

        setContentView(binding.root)

        // ends this activity and goes to sign up page if needed
        binding.gotoSignUp.setOnClickListener {
            val intent = Intent(
                this@SignInActivity,
                SignUpActivity::class.java
            )
            startActivity(intent)
            finish()
        }

        binding.btnSignIn.setOnClickListener {

            // storing the entered email and password
            val email = binding.SImail.text.toString()
            val password = binding.SIpass.text.toString()

            // checks if the values are entered
            if (TextUtils.isEmpty(email) && TextUtils.isEmpty(password)) {
                Toast.makeText(applicationContext,"email and password are required", Toast.LENGTH_SHORT).show()
            }

            // signs in the user using firebase data
            else {
                auth!!.signInWithEmailAndPassword(email, password)
                    .addOnCompleteListener(this) {
                        if (it.isSuccessful) {
                            binding.SImail.setText("")
                            binding.SIpass.setText("")

                            // after sign in takes to user page
                            val intent = Intent(
                                this@SignInActivity,
                                UserActivity::class.java
                            )
                            startActivity(intent)
                            finish()
                        }
                        else {
                            Toast.makeText( applicationContext, "Invalid password or email", Toast.LENGTH_SHORT).show()
                        }
                    }
            }
        }

    }
}

Firebase Authentication causing Android fatal exception

This sounds similar to my problem but still, I couldn't figure why it happens so.

Solution

You never initialize auth, which means that by the time you execute auth!!.signInWithEmailAndPassword(email, password) you get an exception.

Initialize auth like shown in step 2 here in your onCreate to prevent the error.

// Initialize Firebase Auth
auth = Firebase.auth

NullPointerExceptions are very common, so I highly recommend learning how to troubleshoot these yourself. For that, check out:

• What is the Kotlin double-bang (!!) operator?
• Unfortunately MyApp has stopped. How can I solve this?
• What is a NullPointerException, and how do I fix it?

Answered By - Frank van Puffelen