java - 我无法解决尝试在空对象引用上调用虚拟方法 'java.lang.String com.google.firebase.auth.FirebaseUser.getUid()'

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 3 年前。

我在我的处理程序上面临上述问题，该处理程序每​​次都会检查您是否登录，但我面临这个问题，我该如何解决？

伙计们，我已经尝试了几种方法，但我仍然遇到同样的问题，这是每次都会检查的启动屏幕，因此应用程序崩溃了。

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 FirebaseUser 上获取 UID，该 UID 为 null