将Firestore数据提取到自定义对象中 [英] Fetching firestore data into a custom object

问题描述

说onSucces方法下的Toast可以正常工作，但是onSucces之外的Toast不能正常工作

Toast under onSucces method is working but Toast outside onSucces is not working is says

"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()'"

"java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.example.collegecommune.User.getName()' on a null object reference"

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

I am trying to fetch current user data from the firestore and store it in custom class User. I wanted to store documentSnapshot.toObject(User.class) in currentUser.

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();

}

我最近尝试了以下代码: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);
}

推荐答案

通过查看当前的实现，我可以说-您的 onSuccess 调用是异步的&提取数据需要时间&更新 currentUser 对象.到那时，您在 onSuccess 块之外的吐司将执行&尝试从当时的 null 对象的 currentUser 对象中获取数据.因此，它将引发 nullPointetException

By looking at current implementation I can say - your onSuccess call is asynchronous & it'll take time to fetch data & update currentUser object . Till that time your toast which is outside the onSuccess block will execute & try to fetch data from currentUser object which will be null at that point of time.. therefore it throws nullPointetException

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