(user = firebaseAuth.getCurrentUser();)Firebase 用戶在第一次調(diào)用后返回 null 。當(dāng)?shù)谝淮伟惭b應(yīng)用程序時(shí)，它firebaseAuth.getCurrentUser()會(huì)返回用戶，但是當(dāng)它從第一個(gè)活動(dòng)移動(dòng)到另一個(gè)活動(dòng)時(shí)，firebaseAuth.getCurrentUser()每次都會(huì)返回 null 之后調(diào)用 sigh Out 按鈕。package com.example.firebaselogin;import androidx.annotation.NonNull;import androidx.appcompat.app.AppCompatActivity;import android.app.ProgressDialog;import android.content.Intent;import android.os.Bundle;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.firebase.auth.AuthResult;import com.google.firebase.auth.FirebaseAuth;import com.google.firebase.auth.FirebaseUser;public class logIn extends AppCompatActivity {    EditText userName, pwd;    TextView signUpHere;    Button loginButton;    private FirebaseAuth firebaseAuth;    //private FirebaseAuth.AuthStateListener listener;    ProgressDialog progressDialog;    FirebaseUser user;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_log_in);        firebaseAuth = FirebaseAuth.getInstance();        progressDialog = new ProgressDialog(this);        user = firebaseAuth.getCurrentUser();        userName = findViewById(R.id.userName);        pwd = findViewById(R.id.pwd);        signUpHere = findViewById(R.id.signUpHere);        loginButton = findViewById(R.id.loginButton);當(dāng)?shù)趂irebaseAuth.getCurrentUser()一次被調(diào)用時(shí)，它是返回 (2019-08-29 00:08:14.561 8165-8165/com.example.firebaselogin I/Userrrr: com.google.firebase.auth.internal.zzk@44ffb65) 但在下一個(gè)活動(dòng)觸發(fā)注銷后， firebaseAuth.getCurrentUser() 每次都會(huì)返回 null 2019-08-29 00:08:24.651 8165-8165/com.example.firebaselogin I/Userrrr: null``