解决Firestore注册用户时调用collection方法的空指针异常问题

数据老陈

2026-7-15

Firebase注册时保存用户信息到Firestore触发空指针异常

我已经实现了Firebase的账号注册功能，但注册成功后无法将用户详细信息存入Firestore，出现以下空指针异常：

FATAL EXCEPTION: main
Process: com.example.loginapp, PID: 4826
java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.firebase.firestore.CollectionReference com.google.firebase.firestore.FirebaseFirestore.collection(java.lang.String)' on a null object reference

Register.java

package com.example.loginapp;

import static android.content.ContentValues.TAG;

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

import android.content.Intent;
import android.os.Bundle;
import android.text.TextUtils;
import android.util.Log;
import android.view.View;
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.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.android.material.textfield.TextInputEditText;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.firestore.DocumentReference;
import com.google.firebase.firestore.FirebaseFirestore;

import java.util.HashMap;
import java.util.Map;

public class Register extends AppCompatActivity {

    TextInputEditText editTextEmail,editTextPassword;
    EditText nameEditText;
    Button buttonReg;
    ProgressBar progressBar;
    TextView textView;
    FirebaseAuth mAuth;
    FirebaseFirestore fStore;

    public void onStart() {
        super.onStart();
        // Check if user is signed in (non-null) and update UI accordingly.
        FirebaseUser currentUser = mAuth.getCurrentUser();
        if(currentUser != null){
            Intent intent = new Intent(getApplicationContext(), MainActivity.class);
            startActivity(intent);
            finish();
        }
    }

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

        editTextEmail = findViewById(R.id.email);
        editTextPassword = findViewById(R.id.password);
        nameEditText = findViewById(R.id.regi_name);
        buttonReg = findViewById(R.id.btn_register);
        progressBar = findViewById(R.id.progressBar);

        mAuth = FirebaseAuth.getInstance();

        textView = findViewById(R.id.loginNow);

        textView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(getApplicationContext(), Login.class);
                startActivity(intent);
                finish();
            }
        });

        buttonReg.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                progressBar.setVisibility(View.VISIBLE);
                String email, password;

                email = String.valueOf(editTextEmail.getText());
                password = String.valueOf(editTextPassword.getText());

                if (TextUtils.isEmpty(email)){
                    Toast.makeText(Register.this, "Enter Email | NO Email", Toast.LENGTH_SHORT).show();
                    return;
                }

                if (TextUtils.isEmpty(password)){
                    Toast.makeText(Register.this, "Enter Password", Toast.LENGTH_SHORT).show();
                    return;
                }

                mAuth.createUserWithEmailAndPassword(email, password)
                        .addOnCompleteListener(new OnCompleteListener<AuthResult>() {
                            @Override
                            public void onComplete(@NonNull Task<AuthResult> task) {
                                progressBar.setVisibility(View.GONE);

                                if (task.isSuccessful()) {
                                    Toast.makeText(Register.this, "Account successfully created",
                                            Toast.LENGTH_SHORT).show();
                                    // save the user details to DB
                                    FirebaseUser user = mAuth.getCurrentUser();
                                    FirebaseUser currentFirebaseUser = FirebaseAuth.getInstance().getCurrentUser() ;
                                    DocumentReference df = fStore.collection("User").document(user.getUid());
                                    Map<String, Object>userInfo = new HashMap<>();
                                    userInfo.put("Name",nameEditText.getText().toString());
                                    userInfo.put("UserEmail",editTextEmail.getText().toString());
                                     // access level
                                    userInfo.put("isAdmin", "0");

                                    df.set(userInfo);

                                    Intent intent = new Intent(getApplicationContext(), Login.class);
                                    startActivity(intent);
                                    finish();

                                } else {
                                    // If sign in fails, display a message to the user.
                                    Log.w(TAG, "createUserWithEmail:failure", task.getException());
                                    Toast.makeText(Register.this, "Authentication failed.",
                                            Toast.LENGTH_SHORT).show();
                                }
                            }
                        });

            }
        });
    }
}

activity_register.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="15dp"
    android:gravity="center"
    tools:context=".Register">

    <TextView
        android:text="@string/register"
        android:textSize="28sp"
        android:textStyle="bold"
        android:gravity="center"
        android:layout_marginBottom="15dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

    <com.google.android.material.textfield.TextInputLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <com.google.android.material.textfield.TextInputEditText
            android:id="@+id/regi_name"
            android:hint="@string/name"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"/>
    </com.google.android.material.textfield.TextInputLayout>
    <com.google.android.material.textfield.TextInputLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <com.google.android.material.textfield.TextInputEditText
            android:id="@+id/email"
            android:hint="@string/email"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"/>
    </com.google.android.material.textfield.TextInputLayout>


    <com.google.android.material.textfield.TextInputLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <com.google.android.material.textfield.TextInputEditText
            android:id="@+id/password"
            android:hint="@string/password"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"/>
    </com.google.android.material.textfield.TextInputLayout>

    <ProgressBar
        android:id="@+id/progressBar"
        android:visibility="gone"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

    <Button
        android:id="@+id/btn_register"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/btn_register"
        android:layout_margin="10dp"/>
    <TextView
        android:id="@+id/loginNow"
        android:text="@string/click_to_login"
        android:textSize="20sp"
        android:textStyle="bold"
        android:gravity="center"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
</LinearLayout>

解决方法

初始化FirebaseFirestore实例
空指针的核心原因是你只声明了FirebaseFirestore fStore;但没有初始化。在onCreate方法里，给mAuth初始化之后添加一行代码：
```
fStore = FirebaseFirestore.getInstance();
```
位置就在mAuth = FirebaseAuth.getInstance();下方。
简化冗余代码
你在保存用户信息时重复获取了FirebaseUser实例（user和currentFirebaseUser），可以删掉其中一个，比如保留FirebaseUser user = mAuth.getCurrentUser();即可。

添加数据保存结果监听
建议给df.set(userInfo)添加完成监听，以便知道用户信息是否成功存入Firestore，代码示例：

df.set(userInfo).addOnCompleteListener(new OnCompleteListener<Void>() {
    @Override
    public void onComplete(@NonNull Task<Void> task) {
        if(task.isSuccessful()){
            Toast.makeText(Register.this, "用户信息保存成功", Toast.LENGTH_SHORT).show();
        }else{
            Toast.makeText(Register.this, "用户信息保存失败: "+task.getException().getMessage(), Toast.LENGTH_SHORT).show();
        }
    }
});

内容的提问来源于stack exchange，提问作者Noor

解决Firestore注册用户时调用collection方法的空指针异常问题

Register.java #

activity_register.xml #

解决方法 #

Register.java

activity_register.xml

解决方法