java - 将 firestore 数据获取到自定义对象中

Question

onSucces 方法下的 Toast 正常工作，但 onSucces 之外的 Toast 不起作用

“java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“java.lang.String com.example.collegecommune.User.getName()””

我正在尝试从 firestore 获取当前用户数据并将其存储在自定义类 User 中。我想将 documentSnapshot.toObject(User.class) 存储在 currentUser 中。

static FirebaseAuth auth = FirebaseAuth.getInstance();
static FirebaseUser cUser = auth.getCurrentUser();
public static User currentUser;
private FirebaseFirestore db = FirebaseFirestore.getInstance();     


protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    fetchProfile();
    //        currentUser = new FirebaseInteract(this).fetchProfile(cUser);

    setupToolbar();
    navItemSelected();
    //        role = currentUser.getRole();
    //        Toast.makeText(this, currentUser.getName() + "", Toast.LENGTH_SHORT).show();

    if (savedInstanceState == null) {
        navigationView.setCheckedItem(R.id.home);
        getSupportFragmentManager().beginTransaction()
                .replace(R.id.fragment_container, new HomeFragment()).commit();
    }

}

public void fetchProfile() {
    db.collection("users").document(cUser.getEmail()).get()
            .addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {

                @Override
                public void onSuccess(DocumentSnapshot documentSnapshot) {
                    currentUser = documentSnapshot.toObject(User.class);
                    Toast.makeText(MainActivity.this, currentUser.getName() + "", Toast.LENGTH_SHORT).show();
                    Toast.makeText(MainActivity.this, currentUser.getSemester() + "", Toast.LENGTH_SHORT).show();
                    Toast.makeText(MainActivity.this, "Successfully fetched user profile", Toast.LENGTH_SHORT).show();
                }
            }).addOnFailureListener(new OnFailureListener() {
        @Override
        public void onFailure(@NonNull Exception e) {
            Toast.makeText(MainActivity.this, e.getMessage() + "", Toast.LENGTH_SHORT).show();
        }

    });
    Toast.makeText(MainActivity.this, currentUser.getName() + "22", Toast.LENGTH_SHORT).show();
    Toast.makeText(MainActivity.this, currentUser.getSemester() + "22", Toast.LENGTH_SHORT).show();

}

我最近尝试过这段代码:它也不起作用。

 public void fetchProfile(String email) {
    final ProgressDialog dialog = new ProgressDialog(activity);
    dialog.setMessage("Fetching your profile...");
    dialog.show();

    db.collection("users").document(email).get()
            .addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
                @Override
                public void onSuccess(DocumentSnapshot documentSnapshot) {
                    User user1 = documentSnapshot.toObject(User.class);
                    Toast.makeText(activity, user1.getEmail() + " 00", Toast.LENGTH_SHORT).show();
                    MainActivity.setCurrentUser(user1);
                    dialog.dismiss();
                }
            }).addOnFailureListener(onFailureListener);
}

Answer 1

通过查看当前的实现，我可以说 - 您的 onSuccess 调用是异步的，并且需要时间来获取数据和更新 currentUser 对象。到那时，位于 onSuccess block 之外的 toast 将执行并尝试从 currentUser 对象中获取数据，此时该对象将为 null time..因此它抛出 nullPointetException