我无法解决对空对象引用调用虚拟方法'java.lang.String com.google.firebase.auth.FirebaseUser.getUid（）'的尝试

Question

我在处理程序上遇到上述问题，该处理程序每​​次都会检查您是否登录，但我遇到了该如何解决呢？

我尝试了几种方法，但是我仍然遇到相同的问题，即启动屏幕每次都会检查，因此应用程序崩溃。

这是我的欢迎屏幕

```public class WelcomeScreen extends AppCompatActivity {

    private ImageView logo;
    private FirebaseAuth firebaseAuth;
    private FirebaseDatabase firebaseDatabase;
    private static int SPLASH_TIME_OUT = 5000;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setFullscreen ();
        setContentView (R.layout.welcomescreen);
        firebaseAuth = FirebaseAuth.getInstance ();
        final String user_id = firebaseAuth.getCurrentUser ().getUid ();
         final FirebaseUser firebaseUser = firebaseAuth.getInstance ().getCurrentUser ();
        firebaseDatabase = FirebaseDatabase.getInstance ();
       final DatabaseReference databaseReference = firebaseDatabase.getReference ().child ("Users").child (user_id);





        logo= findViewById (R.id.logoocaap);

        Animation animation = AnimationUtils.loadAnimation (this,R.anim.splashscreen);
        logo.startAnimation (animation);



       new Handler ().postDelayed (new Runnable () {
           @Override
           public void run() {


               //check if there's internet connection


               checkConnection();



               if(firebaseUser != null)
               {

                   databaseReference.addValueEventListener (new ValueEventListener () {
                       @Override
                       public void onDataChange(@NonNull DataSnapshot dataSnapshot) {```

Answer 1

首先检查FirebaseUser是否为null，然后尝试获取UID。检查以下内容：

firebaseAuth = FirebaseAuth.getInstance ();
final FirebaseUser firebaseUser = firebaseAuth.getCurrentUser();
String user_id = "";

if(firebaseUser != null)
    user_id = firebaseUser.getUid ();

当前，您尝试在UID的{​​{1}}上获得FirebaseUser

Answer 2

在Firebase控制台中启用登录方法以进行测试以启用登录

更新如下规则

{
  "rules": {
    ".read": true,
    ".write": true
  }
}

然后使用回调函数调用FirebaseAuth.getInstance ().signInAnanymous()，并在成功方法中获取当前用户

示例：

 FirebaseAuth.getInstance ().signInAnonymously().addOnSuccessListener(this, new OnSuccessListener<AuthResult>() {
            @Override
            public void onSuccess(AuthResult authResult) {
                Log.e("TAG", "success sign");
                // do your stuff
            }
        })
                .addOnFailureListener(this, new OnFailureListener() {
                    @Override
                    public void onFailure(@NonNull Exception exception) {
                        Log.e("TAG", "failed sign");
                    }
                });
    }