用户在Rx android和Firebase实时数据库实施中仅调用一次

import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import io.reactivex.Single;
import io.reactivex.android.schedulers.AndroidSchedulers;
import io.reactivex.schedulers.Schedulers;

public class MainActivity extends AppCompatActivity {

    private DatabaseReference databaseReference;

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

        // 获取Firebase实时数据库的引用
        databaseReference = FirebaseDatabase.getInstance().getReference();

        // 使用RxJava控制只调用一次
        Single<DataSnapshot> single = Single.create(emitter -> {
            // 监听数据变化，仅调用一次
            databaseReference.addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    emitter.onSuccess(dataSnapshot);
                }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {
                    emitter.onError(databaseError.toException());
                }
            });
        });

        // 在后台线程执行数据库操作
        single.subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(dataSnapshot -> {
                    // 处理数据
                    // ...
                }, throwable -> {
                    // 处理错误
                    // ...
                });
    }
}