为什么我无法将数组的第一个和最后一个记录记录到Firestore

Question

我正在尝试注册20个用户，并在Firebase Firestore上为每个用户创建一个文档。我的程序成功注册了20个用户，但在为他们创建文档时失败了。每次创建18个，19个文档，但它几乎总是跳过为第一个成员和我的数组的最后一个成员创建一个文档。 StudentCreator只是一个包含父数组的文件，学生数组包含20个项目。这是来自studentCreator.java的数组

public static String parent_names[]={ "Ahmet Lola", "Hüseyin Kutlutürk", "Ümit Uğrak", "Veysel Karani", "Serkan Gotar", "Dündar Zalim", "Kadir Berkay", "Uğur Özdemir", "Bünyamin Akgün", "Kaptan Price", "Selim Tekiner", "Gökçe Yılan", "Talip Özkan", "Abdurrahman Tarikçi", "Selim Kirlier", "Hasan Can Doğan", "Erdem Gökşen", "Fatoş Ünal", "Nurgül Birtek", "Yuan Hui"};

这里的主要代码：

    public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";
private FirebaseAuth mAuth;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    final Intent LoginActivity = new Intent(this,LoginActivity.class);
    final Intent TeacherActivity = new Intent(this,TeacherActivity.class);
    final Intent ParentActivity = new Intent(this,ParentActivity.class);
    final Intent ManagerActivity = new Intent(this,ManagerActivity.class);


    for (int i = 0; i < 20; i++)
    {
        mAuth = FirebaseAuth.getInstance();
        final String username = StudentCreator.parent_names[i].replaceAll(" ", "") + StudentCreator.student_numbers[i];
        final String email = username + "@onurmail.com";
        final String password = "123456";

        final String student_name = StudentCreator.student_names[i];
        final String parent_name = StudentCreator.parent_names[i];
        //Registration is successul here.
        mAuth.createUserWithEmailAndPassword(email, password)
                .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        if (task.isSuccessful()) {
                            // Sign in success, update UI with the signed-in user's information
                            Log.d("User Registered", "createUserWithEmail:success");

                            final FirebaseUser user = mAuth.getCurrentUser();
                            final String user_id = user.getUid();
                            //I get valid userId's for 20 users.
                            //CREATE STUDENT OBJECT AND FIREBASE INSTANCES
                            final FirebaseFirestore db = FirebaseFirestore.getInstance();

                            final Map<String, Object> student = new HashMap<>();
                            student.put("student_name", student_name);
                            student.put("parent_name", parent_name);
                            //My first element of array comes here and prints its parent name and student name perfectly but cant see anything about it on database.
                            //PUT STUDENT TO THE DB
                            db.collection("TED_Ankara")
                                    .document(parent_name)
                                    .set(student)
                                    .addOnCompleteListener(new OnCompleteListener<Void>() {
                                        @Override
                                        public void onComplete(@NonNull Task<Void> task) {
                                            if (task.isSuccessful()) {
                                                Toast.makeText(getApplicationContext(), "User  inserted sucessfully: "+parent_name,
                                                        Toast.LENGTH_SHORT).show();

                                            }
                                            else {
                                                Toast.makeText(getApplicationContext(), "User cannot be inserted: "+parent_name,
                                                        Toast.LENGTH_SHORT).show();
                                            }

                                        }
                                    });

                            //PUT STUDENT TO THE DB



                        } else {
                            // If sign in fails, display a message to the user.
                            Log.w(TAG, "createUserWithEmail:failure", task.getException());
                            Toast.makeText(getApplicationContext(), "Authentication failed.",
                                    Toast.LENGTH_SHORT).show();
                        }

                    }

                });

    }
  }
}

请帮忙。我对addOnCompleteListener和firebaseAuth的用法持怀疑态度。但我不确定。谢谢你的帮助。

编辑：添加没有for循环的第一个成员没有任何问题。所以我猜问题是关于for循环。