为什么我不能在方法之外调用变量？[副本]

Question

在这个解决方案中，我可以调用void中的变量。当我试图在void之外调用它时，数据是空的。

public class FormSendActivity extends AppCompatActivity {

// form edit text
EditText email ;
EditText perihal;
EditText deskripsi;

TextView tes;

// variabel untuk menyimpan data dari edit text menjadi string
public String emails;
public String perihals;
public String deskripsis;

//variabel untuk menampung datauser sesuai login
public String getnama;
public String getusername;

FirebaseAuth firebaseAuth;
public String uid ;

Button kirim;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_form_send);


    email = (EditText) findViewById(R.id.editText);
    perihal = (EditText) findViewById(R.id.editText2);
    deskripsi = (EditText) findViewById(R.id.editText4);
    kirim = (Button) findViewById(R.id.button);
    tes = (TextView) findViewById(R.id.textView3);

    firebaseAuth = firebaseAuth.getInstance();
    uid = firebaseAuth.getCurrentUser().getUid();

    dapatdatauser(uid);  // here i call the method of bottom, and put in to a variabel
    tes.setText(getusername); //  here i put the variabel to textview to test

    kirim.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            emails = email.getText().toString();
            perihals = perihal.getText().toString();
            deskripsis = deskripsi.getText().toString();

            Sendmail sendmail = new Sendmail(emails,perihals,deskripsis);
            FirebaseDatabase.getInstance().getReference("Sendmail")
                    .child(getusername).child("Outbox").push()
                    .setValue(sendmail).addOnCompleteListener(new OnCompleteListener<Void>() {
                @Override
                public void onComplete(@NonNull Task<Void> task) {
                    if (task.isSuccessful()){
                        Toast.makeText(FormSendActivity.this,"Data sudah terkirim !!", Toast.LENGTH_SHORT).show();
                        Intent i = new Intent(FormSendActivity.this, MainActivity.class);
                        finish();
                    }else {
                        Toast.makeText(FormSendActivity.this,"Data gagal di kirim !!", Toast.LENGTH_SHORT).show();
                    }
                }
            });
        }
    });


}

public void dapatdatauser(String iduser){
    // Mendapatkan DataUsers Berdasarkan uid sesuai login
    DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
    DatabaseReference query = reference.child("DataUsers").child(iduser);
    ValueEventListener valueEventListener = new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            // Memasukkan data kedalam variabel username
            getusername = dataSnapshot.child("username").getValue(String.class);

        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    };
    query.addListenerForSingleValueEvent(valueEventListener);
}} 

public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        // Memasukkan data kedalam variabel username
        getusername = dataSnapshot.child("username").getValue(String.class);

    }

但我只想知道，为什么我的代码一开始就不能工作？谢谢。

Answer 1

但是我只想知道，为什么我的代码中的第一个函数不是？

您无法获得getusername值，因为它是异步操作。数据尚未从数据库加载完毕，这就是无法访问的原因。