進入注冊活動后，我的應用程式立即出現空指標例外，我無法找出原因-有解無憂

問題這是注冊活動的代碼，我想讓用戶注冊并在實時資料庫中添加用戶名和用戶 ID 詳細資訊。但是打開注冊活動后應用程式崩潰了

錯誤

FATAL EXCEPTION: main
                 Process: com.example.movies4u, PID: 18933
                 java.lang.NullPointerException: Attempt to invoke interface method 'void com.google.firebase.auth.FirebaseAuth$AuthStateListener.onAuthStateChanged(com.google.firebase.auth.FirebaseAuth)' on a null object reference
                    at com.google.firebase.auth.zzl.run(com.google.firebase:firebase-auth@@21.0.3:1)
                    at android.os.Handler.handleCallback(Handler.java:873)
                    at android.os.Handler.dispatchMessage(Handler.java:99)
                    at android.os.Looper.loop(Looper.java:224)
                    at android.app.ActivityThread.main(ActivityThread.java:7081)
                    at java.lang.reflect.Method.invoke(Native Method)
                    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:604)
                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:928)

爪哇

package com.example.movies4u;

import static android.content.ContentValues.TAG;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.annotation.SuppressLint;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

import com.example.movies4u.Utils.FirebaseMethods;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.OnFailureListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseAuthUserCollisionException;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;

public class activity_register extends AppCompatActivity {
    TextView HaveAccount;
    EditText inputUsername,inputEmail,inputPassword,inputConfirmPassword;
    String username,email,password;
    Button btnRegister;
    FirebaseAuth mAuth;
    ProgressBar pb;
    private String userID;
    private FirebaseAuth.AuthStateListener mAuthListener;
    private FirebaseMethods firebaseMethods;
    private FirebaseDatabase mFirebaseDatabase;
    private DatabaseReference myRef;

    private String append;

    @SuppressLint("MissingInflatedId")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,WindowManager.LayoutParams.FLAG_FULLSCREEN); //Hide status Bar
        setContentView(R.layout.activity_register);
        firebaseMethods =new FirebaseMethods(activity_register.this);

        HaveAccount= (TextView) findViewById(R.id.HaveAccount);
        pb = findViewById(R.id.progressBar3);
        inputUsername=findViewById(R.id.inputUsername);
        inputEmail=findViewById(R.id.inputEmail);
        inputPassword=findViewById(R.id.inputPassword);
        inputConfirmPassword=findViewById(R.id.inputConfirmPassword);
        btnRegister=findViewById(R.id.btnRegister);
        username=inputUsername.getText().toString();
        email=inputEmail.getText().toString();
        password=inputPassword.getText().toString();

        pb.setVisibility(View.GONE);
        HaveAccount.setOnClickListener(view -> {
            Intent loginintent=new Intent(activity_register.this,login_activity.class);
            startActivity(loginintent);
        });

        mAuth=FirebaseAuth.getInstance();
        btnRegister.setOnClickListener(view -> ValidateDataandDoRegister());
    }

    private void ValidateDataandDoRegister() {
        String username=inputUsername.getText().toString().trim();
        String email=inputEmail.getText().toString().trim();
        String password=inputPassword.getText().toString().trim();
        String confirmPassword=inputConfirmPassword.getText().toString().trim();
        if(email.isEmpty()){
            inputEmail.setError("Enter Email Address");
            inputEmail.requestFocus();
            pb.setVisibility(View.GONE);
        }
        else if(email.length()<10){
            inputEmail.setError("Enter valid Email");
            inputEmail.requestFocus();
            pb.setVisibility(View.GONE);
        }
        else if(password.isEmpty()){
            inputPassword.setError("Enter the password");
            inputPassword.requestFocus();
            pb.setVisibility(View.GONE);
        }
        else if(password.length()<8){
            inputPassword.setError("Password should be greater than 8 characters");
            inputPassword.requestFocus();
            pb.setVisibility(View.GONE);
        }
        else if(confirmPassword.isEmpty()){
            inputConfirmPassword.setError("Re-Enter the Password");
            inputConfirmPassword.requestFocus();
            pb.setVisibility(View.GONE);
        }
        else if(confirmPassword.length()<8){
            inputConfirmPassword.setError("Password should be greater than 8 characters");
            inputConfirmPassword.requestFocus();
            pb.setVisibility(View.GONE);
        }
        else if(!password.equals(confirmPassword)){
            inputPassword.setError("Password not matched");
            inputPassword.requestFocus();
            inputConfirmPassword.setError("Password not matched");
            inputConfirmPassword.requestFocus();
            inputPassword.setText("");
            inputConfirmPassword.setText("");
            pb.setVisibility(View.GONE);
        }
        else{
            pb.setVisibility(View.VISIBLE);
            doRegister(username,email,password);
        }
    }

    private void doRegister(String username,String email, String password) {
        pb.setVisibility(View.VISIBLE);
        mAuth.createUserWithEmailAndPassword(email, password).addOnSuccessListener(task -> {
            if(task != null ){
                if(mAuth.getCurrentUser() != null){
                    userID=mAuth.getCurrentUser().getUid();
                }

//                firebaseMethods.registerNewEmail(username,email,password);
                setupFirebaseAuth();
                sendVerificationEmail();
//                firebaseMethods.addNewUser(email, username);
            }

        }).addOnFailureListener(e -> {
            if(e instanceof FirebaseAuthUserCollisionException){
                btnRegister.setEnabled(true);
                inputEmail.setError("Email Already Registered");
                pb.setVisibility(View.GONE);
                inputEmail.requestFocus();
            }
            else{
                btnRegister.setEnabled(true);
                pb.setVisibility(View.GONE);
                Toast.makeText(activity_register.this, "Oops! Something Went wrong", Toast.LENGTH_SHORT).show();
            }
        });
    }

    private void sendVerificationEmail() {
        mAuth.getCurrentUser().sendEmailVerification().addOnCompleteListener(task -> {
            if(task != null && task.isSuccessful()){
                btnRegister.setEnabled(true);
                pb.setVisibility(View.GONE);
                Toast.makeText(activity_register.this, "Email has been sent to your email address", Toast.LENGTH_SHORT).show();
                //fixing the bug
                mAuth.signOut();
            }
            else {
                btnRegister.setEnabled(true);
                pb.setVisibility(View.GONE);
                Toast.makeText(getApplicationContext(), "Oops! failed to send verification email",Toast.LENGTH_SHORT).show();
            }
        });
    }


    /*
    ------------------------------------ Firebase ---------------------------------------------
     */

    /**
     * Setup the firebase auth object
     */
    private void setupFirebaseAuth(){
        Log.d(TAG, "setupFirebaseAuth: setting up firebase auth.");

        mAuth = FirebaseAuth.getInstance();
        mFirebaseDatabase = FirebaseDatabase.getInstance();
        myRef = mFirebaseDatabase.getReference();

        //cannot get into this part of code
        mAuthListener = new FirebaseAuth.AuthStateListener() {
            @Override
            public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
                FirebaseUser user=firebaseAuth.getCurrentUser();
                if (user != null) {
                    // User is signed in
                    Log.d(TAG, "onAuthStateChanged:signed_in:"   user.getUid());

                    myRef.addValueEventListener(new ValueEventListener() {
                        @Override
                        public void onDataChange(DataSnapshot dataSnapshot) {
                            //1st check: Make sure the username is not already in use
                            if(firebaseMethods.checkIfUsernameExists(username, dataSnapshot)){
                                //to randomly generate key to make sure username is unique
                                append = myRef.push().getKey().substring(3,10);
                                Log.d(TAG, "onDataChange: username already exists. Appending random string to name: "   append);
                            }
                            username = username   append;

                            //add new user to the database
//                            firebaseMethods.addNewUser(email, username);
                            Toast.makeText(activity_register.this, "SignUp successful", Toast.LENGTH_SHORT).show();
                        }

                        @Override
                        public void onCancelled(DatabaseError databaseError) {
                            Toast.makeText(activity_register.this, "unsuccessful", Toast.LENGTH_SHORT).show();
                        }
                    });
                    finish();

                } else {
                    // User is signed out
                    Toast.makeText(activity_register.this, "unsuccessful", Toast.LENGTH_SHORT).show();
                    Log.d(TAG, "onAuthStateChanged:signed _out");
                }
                // ...
            }
        };
    }

    @Override
    public void onStart() {
        super.onStart();
        mAuth.addAuthStateListener(mAuthListener);
    }

    @Override
    public void onStop() {
        super.onStop();
        if (mAuthListener != null) {
            mAuth.removeAuthStateListener(mAuthListener);
        }
    }

}

我期望將用戶資料存盤在實時資料庫中。但是在我進入注冊活動后，我得到了一個空指標例外。我想這是因為空用戶。但是我應該得到一個非空用戶，因為在用戶單擊注冊按鈕并驗證所有欄位之后，我正在實作該方法。

uj5u.com熱心網友回復：

您的代碼流程是錯誤的。您將 AuthListener 添加到onStart()asmAuth.addAuthStateListener(mAuthListener);但mAuthListener稍后在中對其進行初始化doRegiter()，這意味著在將其添加到時onStart()，它沒有被初始化并且 null 會給出錯誤Null Pointer Exception。

對于解決方案，您應該在將其添加到 as 之前呼叫setUpFirebaseAuth該onStart函式mAuth：

@Override
public void onStart() {
    super.onStart();
    setupFirebaseAuth();
    mAuth.addAuthStateListener(mAuthListener);
}

轉載請註明出處，本文鏈接：https://www.uj5u.com/ruanti/522384.html

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