如何从Firebase实时数据库中完全删除该值？

Question

我尝试了removeValue和setvalue(null)，但它仍然用null替换基中的值。

import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

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 com.google.firebase.database.ValueEventListener;

import java.util.Map;

public class MainActivity extends AppCompatActivity {

    Button mButtonSee;
    TextView mTextViewPromo;

    DatabaseReference mRef = FirebaseDatabase.getInstance().getReference();
    DatabaseReference mPromoRef =                 
mRef.child("delivery").child("0").child("promokod");

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

        mButtonSee = findViewById(R.id.buttonSee);
        mTextViewPromo = findViewById(R.id.promo);

        mButtonSee.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                mPromoRef.addListenerForSingleValueEvent(new 
ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    String text = dataSnapshot.getValue(String.class);
                    mTextViewPromo.setText(text);
                    mPromoRef.removeValue();
                }

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

                    }

                });

            }
        });

    }
}

因此，我想在单击按钮时从第一个数组中获取一个值，然后删除它，再次从新的第一个数组中获取值。

它的数据库结构：

我的新代码：

public class MainActivity extends AppCompatActivity {


Button mButtonSee;
TextView mTextViewPromo;


DatabaseReference mRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference mPromoRef = mRef.child("delivery");


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


    mButtonSee = findViewById(R.id.buttonSee);
    mTextViewPromo = findViewById(R.id.promo);


    mButtonSee.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            mPromoRef.addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    LinkedList<String> values = new LinkedList<>();
                    boolean isFirst = true;
                    for (DataSnapshot codeSnapshot: dataSnapshot.getChildren()) {
                        if (isFirst) {
                            isFirst = false;
                        }
                        else {
                            String text = codeSnapshot.getValue(String.class);
                            values.add(text);
                        }
                    }
                    mPromoRef.setValue(values);
                }

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

            });

        }
    });

}
}

logcat：2019-02-20 02:11:25.263 163 1-2110/？E/AudioFlinger：内存不足，无法容纳AudioTrack大小=131296

2019-02-20 02:11:25.263 163 1-2110/？E/AudioFlinger:createRecordTrack_l()initCheck失败-12；没有控制块？

2019-02-20 02:11:25.271 265 1-11949/com.google.android.googleQuickSearchbox：搜索E/AudioreCord-JNI：创建AudioRecord实例时出错：初始化检查失败，状态为-12。

2019-02-20 02:11:25.274 265 1-11949/com.google.android.googleQuickSearchbox：search e/android.media.AudioRecord：初始化本机AudioRecord对象时错误代码-20。

2019-02-20 02:11:25.274 265 1-11949/com.google.android.googleQuickSearchBox：Search I/MicrophoneInputStream:mic_started SR:16000 CC:16 SO：6

2019-02-20 02:11:25.275 265 1-11949/com.google.android.googleQuickSearchBox：Search E/ActivityThread：未能找到com.google.android.apps.gsa.testing.ui.audio.Recorded的提供商信息

运行：

Answer 1

null