如何在实时数据库中获取特定的密钥

Question

我目前在从firebase中删除特定数据时遇到问题。所以基本上我有一个循环视图，其中显示了我的数据，每个数据显示中都有一个按钮，那就是编辑按钮。每当我尝试单击"编辑"按钮时，它都会让我进入另一个活动，该活动具有在回收视图中显示的相同数据，并且会显示另一个按钮，即"删除"按钮。但每当我尝试单击删除按钮时，它都会删除子项中的所有数据。我只需要删除在意图发生时通过的选定ID/Data。编辑

EditResearch.java

package com.example.citeresearchrepository.AdminPackage;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Toast;
import com.example.citeresearchrepository.Model.ResearchRepository;
import com.example.citeresearchrepository.R;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.OnFailureListener;
import com.google.android.gms.tasks.OnSuccessListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.storage.FirebaseStorage;
import com.google.firebase.storage.OnProgressListener;
import com.google.firebase.storage.StorageReference;
import com.google.firebase.storage.UploadTask;
public class EditResearchActivity extends AppCompatActivity {
EditText editfilehandler_et,editrepo_title,editrepo_description,editrepo_currentdate;
Button editrepo_savebtn;
ImageView backbtn_editresearch;
DatabaseReference databaseReference;
FirebaseDatabase firebaseDatabase;
StorageReference storageReference;
String researchtitle,researchdate,researchname,researchdescription;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_edit_research);
editfilehandler_et = findViewById(R.id.editfilehandler_et);
editrepo_title = findViewById(R.id.editrepo_title);
editrepo_description = findViewById(R.id.editrepo_description);
editrepo_currentdate = findViewById(R.id.editrepo_currentdate);
editrepo_savebtn = findViewById(R.id.editrepo_savebtn);
backbtn_editresearch = findViewById(R.id.backbtn_editresearch);
Intent intent = getIntent();
researchtitle = intent.getStringExtra("researchtitle");
researchdate = intent.getStringExtra("researchdate");
researchname = intent.getStringExtra("researchname");
researchdescription = intent.getStringExtra("researchdescription");
databaseReference = FirebaseDatabase.getInstance().getReference("ResearchRepository");
storageReference = FirebaseStorage.getInstance().getReference();
editfilehandler_et.setText(researchname);
editrepo_title.setText(researchtitle);
editrepo_currentdate.setText(researchdate);
editrepo_description.setText(researchdescription);
editrepo_savebtn.setEnabled(false);
editfilehandler_et.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
selectPDF();
}
});
/* Update Files */
backbtn_editresearch.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(getApplicationContext(), AdminResearchRepoActivity.class));
}
});
}
private void selectPDF(){
Intent intent = new Intent();
intent.setType("application/pdf");
intent.setAction(intent.ACTION_GET_CONTENT);
startActivityForResult(Intent.createChooser(intent, "PDF FILE SELECTED"), 12);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable final Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if(requestCode==12 && resultCode == RESULT_OK && data!=null && data.getData()!=null){
editrepo_savebtn.setEnabled(true);
editfilehandler_et.setText(data.getDataString().substring(data.getDataString().lastIndexOf("/") + 1));
editrepo_savebtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
deletePreviousImage();
uploadResearch(data.getData());
}
});
}
}
private void deleteSelectedRow(){
firebaseDatabase = FirebaseDatabase.getInstance();
databaseReference = firebaseDatabase.getReference("ResearchRepository");
databaseReference.removeValue();
}
private void uploadResearch(Uri data) {
final String filecapture = editfilehandler_et.getText().toString();
final String researchtitle = editrepo_title.getText().toString();
final String researchdescription = editrepo_description.getText().toString();
final String researchtimeline = editrepo_currentdate.getText().toString();
final ProgressDialog progressDialog = new ProgressDialog(this);
progressDialog.setTitle("File Uploading...");
progressDialog.show();
StorageReference reference = storageReference.child("ResearchRepository" +System.currentTimeMillis() + ".pdf");
reference.putFile(data).addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() {
@Override
public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {
Task<Uri> uriTask = taskSnapshot.getStorage().getDownloadUrl();
while(!uriTask.isComplete());
Uri uri = uriTask.getResult();
ResearchRepository researchRepository = new ResearchRepository(filecapture,researchtitle,researchdescription,researchtimeline,uri.toString());
databaseReference.child(databaseReference.push().getKey()).setValue(researchRepository);
Toast.makeText(EditResearchActivity.this, "File Uploaded", Toast.LENGTH_SHORT).show();
progressDialog.dismiss();
editfilehandler_et.setText("");
editrepo_title.setText("");
editrepo_currentdate.setText("");
editrepo_description.setText("");
startActivity(new Intent(getApplicationContext(), AdminResearchRepoActivity.class));
}
}).addOnProgressListener(new OnProgressListener<UploadTask.TaskSnapshot>() {
@Override
public void onProgress(@NonNull UploadTask.TaskSnapshot snapshot) {
double progress = (100*snapshot.getBytesTransferred())/snapshot.getTotalByteCount();
progressDialog.setMessage("File Uploading..."+(int)progress+"%");
}
});
}
private void deletePreviousImage(){
StorageReference reference = FirebaseStorage.getInstance().getReference().child(researchtitle);
reference.delete().addOnSuccessListener(new OnSuccessListener<Void>() {
@Override
public void onSuccess(Void aVoid) {
Toast.makeText(EditResearchActivity.this, "Previous File Deleted", Toast.LENGTH_SHORT).show();
}
}).addOnFailureListener(new OnFailureListener() {
@Override
public void onFailure(@NonNull Exception e) {
Toast.makeText(EditResearchActivity.this, e.getMessage(), Toast.LENGTH_SHORT).show();
}
});
}
}

AdminResearchRepoActivity.java

package com.example.citeresearchrepository.AdminPackage;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.Toast;
import com.example.citeresearchrepository.AdminAdapter.AdminRepoAdapter;
import com.example.citeresearchrepository.Model.ResearchRepository;
import com.example.citeresearchrepository.R;
import com.example.citeresearchrepository.ViewHolder.AdminResearchRepositoryViewHolder;
import com.firebase.ui.database.FirebaseRecyclerAdapter;
import com.firebase.ui.database.FirebaseRecyclerOptions;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
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.ArrayList;
public class AdminResearchRepoActivity extends AppCompatActivity {
ImageView adminrepo_backbtn;
RecyclerView reporecycler;
FloatingActionButton addresearch_btn;
FirebaseDatabase firebaseDatabase;
DatabaseReference databaseReference;
AdminRepoAdapter adminRepoAdapter;
ArrayList<ResearchRepository> researchRepositoryArrayList = new ArrayList<>();

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_admin_research_repo);
//      Buttons
adminrepo_backbtn = findViewById(R.id.backbtn_adminrepo);
addresearch_btn = findViewById(R.id.addresearch_btn);
addresearch_btn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(getApplicationContext(), AddResearchActivity.class));
}
});
adminrepo_backbtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(getApplicationContext(), WelcomeAdminActivity.class));
}
});
//      Recycler
reporecycler = findViewById(R.id.reporecycler);
reporecycler.setLayoutManager(new LinearLayoutManager(this));
//      Firebase Connection
firebaseDatabase = FirebaseDatabase.getInstance();
databaseReference = FirebaseDatabase.getInstance().getReference().child("ResearchRepository");
databaseReference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
researchRepositoryArrayList = new ArrayList<ResearchRepository>();
for (DataSnapshot dataSnapshot: snapshot.getChildren()){
ResearchRepository researchRepository = dataSnapshot.getValue(ResearchRepository.class);
researchRepositoryArrayList.add(researchRepository);
}
adminRepoAdapter = new AdminRepoAdapter(AdminResearchRepoActivity.this,researchRepositoryArrayList);
reporecycler.setAdapter(adminRepoAdapter);
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
Toast.makeText(AdminResearchRepoActivity.this, error.getMessage(), Toast.LENGTH_SHORT).show();
}
});
}
}

AdminRepoAdapter.java

package com.example.citeresearchrepository.AdminAdapter;
import android.content.Context;
import android.content.Intent;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import com.example.citeresearchrepository.AdminPackage.EditResearchActivity;
import com.example.citeresearchrepository.Model.ResearchRepository;
import com.example.citeresearchrepository.R;
import java.lang.reflect.Array;
import java.util.ArrayList;
public class AdminRepoAdapter extends RecyclerView.Adapter<AdminRepoAdapter.AdminViewHolder>  {
Context context;
ArrayList<ResearchRepository> researchRepositories;
public AdminRepoAdapter(Context c, ArrayList<ResearchRepository> repositories){
context = c;
researchRepositories = repositories;
}
@NonNull
@Override
public AdminViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
return new AdminViewHolder(LayoutInflater.from(context).inflate(R.layout.admineditrepo_row,parent,false));
}
@Override
public void onBindViewHolder(@NonNull AdminViewHolder holder, final int position) {
holder.researchtitle_view.setText(researchRepositories.get(position).getResearchtitle());
holder.researchdate_view.setText(researchRepositories.get(position).getResearchtimeline());
holder.researchname_view.setText(researchRepositories.get(position).getFilecapture());
holder.researchdescription_view.setText(researchRepositories.get(position).getResearchdescription());
holder.btnpdf_edit.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(context, EditResearchActivity.class);
intent.putExtra("researchtitle",researchRepositories.get(position).getResearchtitle());
intent.putExtra("researchdate",researchRepositories.get(position).getResearchtimeline());
intent.putExtra("researchname",researchRepositories.get(position).getFilecapture());
intent.putExtra("researchdescription",researchRepositories.get(position).getResearchdescription());
v.getContext().startActivity(intent);
}
});
}
@Override
public int getItemCount() {
return researchRepositories.size();
}
class AdminViewHolder extends RecyclerView.ViewHolder{
public TextView researchtitle_view,researchdate_view,researchname_view,researchdescription_view,researchtitle_url;
public Button btnpdf_edit;
public AdminViewHolder (@NonNull View itemView) {
super(itemView);
researchtitle_view = itemView.findViewById(R.id.researchtitle_view);
researchdate_view = itemView.findViewById(R.id.researchdate_view);
researchname_view = itemView.findViewById(R.id.researchname_view);
researchdescription_view = itemView.findViewById(R.id.researchdescription_view);
researchtitle_url = itemView.findViewById(R.id.researchtitle_view);
btnpdf_edit = itemView.findViewById(R.id.btnpdf_edit);
}
}
}

ResearchRepository.class

package com.example.citeresearchrepository.Model;
public class ResearchRepository {
public String filecapture;
public String researchtitle;
public String researchdescription;
public String researchtimeline;
public String url;
public ResearchRepository() {
}
public ResearchRepository(String filecapture, String researchtitle, String researchdescription, String researchtimeline, String url) {
this.filecapture = filecapture;
this.researchtitle = researchtitle;
this.researchdescription = researchdescription;
this.researchtimeline = researchtimeline;
this.url = url;
}
public String getFilecapture() {
return filecapture;
}
public void setFilecapture(String filecapture) {
this.filecapture = filecapture;
}
public String getResearchtitle() {
return researchtitle;
}
public void setResearchtitle(String researchtitle) {
this.researchtitle = researchtitle;
}
public String getResearchdescription() {
return researchdescription;
}
public void setResearchdescription(String researchdescription) {
this.researchdescription = researchdescription;
}
public String getResearchtimeline() {
return researchtimeline;
}
public void setResearchtimeline(String researchtimeline) {
this.researchtimeline = researchtimeline;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
}

这是我的实时数据库：https://i.stack.imgur.com/lML0i.png我只想删除红框。

Answer 1

据我所见，您正在将一个实例仅发送到ResearchRepository节点，而不是要删除的特定子节点。您需要跟踪推送到ResearchRepository节点的唯一ID，并在意图中传递它；

添加代码以传递要删除的ResearchRepository子级的唯一ID。然后在出现删除代码的新活动中执行此操作。

String childToDelete; //retrieve the value from the intent
DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference("ResearchRepository").child(childToDelete);
databaseReference.removeValue();

如果这是你的目的，那就应该这样做。

编辑1：-我明白你的意思。请按照我现在展示的方法，它会对你起作用。

编辑你的课程如下所示：-

AdminRepoAdapter.java

public class AdminRepoAdapter extends RecyclerView.Adapter<AdminRepoAdapter.AdminViewHolder>  {
Context context;
Map<String,ResearchRepository> researchRepositories;
ArrayList<ResearchRepository> researchRepositoriesHolder;
public AdminRepoAdapter(Context c, Map<String,ResearchRepository> repositories){
context = c;
researchRepositories = repositories;
researchRepositoriesHolder = new ArrayList<>(researchRepositories.values());
}
@NonNull
@Override
public AdminViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
return new AdminViewHolder(LayoutInflater.from(context).inflate(R.layout.admineditrepo_row,parent,false));
}
@Override
public void onBindViewHolder(@NonNull AdminViewHolder holder, final int position) {
holder.researchtitle_view.setText(researchRepositoriesHolder.get(position).getResearchtitle());
holder.researchdate_view.setText(researchRepositoriesHolder.get(position).getResearchtimeline());
holder.researchname_view.setText(researchRepositoriesHOlder.get(position).getFilecapture());
holder.researchdescription_view.setText(researchRepositoriesHolder.get(position).getResearchdescription());
holder.btnpdf_edit.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Map.Entry<String,ResearchRepository> entry = null; //Just for initialization
for (Map.Entry<String,ResearchRepository> var : researchRepositories.entrySet()) {
if(var.getValue() == researchRepositoriesHolder.get(position)){
entry = var;
break;
}
}
Intent intent = new Intent(context, EditResearchActivity.class);
intent.putExtra("researchtitle",entry.getValue().getResearchtitle());
intent.putExtra("researchdate",entry.getValue().getResearchtimeline());
intent.putExtra("researchname",entry.getValue().getFilecapture());
intent.putExtra("researchdescription",entry.getValue().getResearchdescription());
intent.putExtra("childNodeKey",entry.getKey());
v.getContext().startActivity(intent);
}
});
}
@Override
public int getItemCount() {
return researchRepositoriesHolder.size();
}
class AdminViewHolder extends RecyclerView.ViewHolder{
public TextView researchtitle_view,researchdate_view,researchname_view,researchdescription_view,researchtitle_url;
public Button btnpdf_edit;
public AdminViewHolder (@NonNull View itemView) {
super(itemView);
researchtitle_view = itemView.findViewById(R.id.researchtitle_view);
researchdate_view = itemView.findViewById(R.id.researchdate_view);
researchname_view = itemView.findViewById(R.id.researchname_view);
researchdescription_view = itemView.findViewById(R.id.researchdescription_view);
researchtitle_url = itemView.findViewById(R.id.researchtitle_view);
btnpdf_edit = itemView.findViewById(R.id.btnpdf_edit);
}
}
}

AdminResearchRepoActivity.java

public class AdminResearchRepoActivity extends AppCompatActivity {
ImageView adminrepo_backbtn;
RecyclerView reporecycler;
FloatingActionButton addresearch_btn;
FirebaseDatabase firebaseDatabase;
DatabaseReference databaseReference;
AdminRepoAdapter adminRepoAdapter;
Map<String, ResearchRepository> researchRepositoryMap;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_admin_research_repo);
//      Buttons
adminrepo_backbtn = findViewById(R.id.backbtn_adminrepo);
addresearch_btn = findViewById(R.id.addresearch_btn);
addresearch_btn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(getApplicationContext(), AddResearchActivity.class));
}
});
adminrepo_backbtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(getApplicationContext(), WelcomeAdminActivity.class));
}
});
//      Recycler
reporecycler = findViewById(R.id.reporecycler);
reporecycler.setLayoutManager(new LinearLayoutManager(this));
//      Firebase Connection
firebaseDatabase = FirebaseDatabase.getInstance();
databaseReference = FirebaseDatabase.getInstance().getReference().child("ResearchRepository");
databaseReference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
researchRepositoryMap = (Map)snapshot.getValue()
adminRepoAdapter = new AdminRepoAdapter(AdminResearchRepoActivity.this,researchRepositoryMap);
reporecycler.setAdapter(adminRepoAdapter);
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
Toast.makeText(AdminResearchRepoActivity.this, error.getMessage(), Toast.LENGTH_SHORT).show();
}
});
}
}

通过这种方式，当您将意向从AdminRepoAdapter传递到EditResearchActivity时，您将在意向中将密钥存储为"childNodeKey"。然后，您可以按照我在编辑之前提到的程序，使用您从这里获得的密钥进行删除。