RecyclerView显示关闭并返回活动后的数据

Question

我正在使用RecyclerView显示从firebase实时数据库获取的数据。当我打开回收者视图活动时，它什么都不显示，但当我转到前一个活动时，再次出现，它就会显示。

这是必须显示数据的活动-

public class BrakesItemActivity extends AppCompatActivity {
private RecyclerView recyclerView;
private FloatingActionButton floatingActionButton;
private FirebaseDatabase database;
private DatabaseReference BrakestransactionDb, brakesDb;
private FirebaseRecyclerOptions<Transaction> options;
private FirebaseRecyclerAdapter<Transaction, TransactionViewHolder> adapter;
int sumofbrakescost = 0;
String sumofbrakescostvalue;
BottomAppBar bottomAppBar;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_last2);
bottomAppBar = findViewById(R.id.bottom_app_bar);
recyclerView = findViewById(R.id.recycler_view);
floatingActionButton = findViewById(R.id.floating_button);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS,
WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS);
setSupportActionBar(bottomAppBar);
floatingActionButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(BrakesItemActivity.this, BInputActivity.class);
startActivity(intent);
}
});
database = FirebaseDatabase.getInstance();
BrakestransactionDb = database.getReference().child("Brakes Items Transaction");
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(BrakesItemActivity.this));
BrakestransactionDb.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot ds : dataSnapshot.getChildren()) {
Map<String, Object> map = (Map<String, Object>) ds.getValue();
Object totalcost = map.get("totalcoststring");
int totalcostvalue = Integer.parseInt(String.valueOf(totalcost));
sumofbrakescost += totalcostvalue;
sumofbrakescostvalue = String.valueOf(sumofbrakescost);
}
brakesDb = database.getReference().child("Department").child("Brakes").child("Cost");
brakesDb.setValue(sumofbrakescostvalue);
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
showTask();
}
private void showTask() {
options = new FirebaseRecyclerOptions.Builder<Transaction>().setQuery(BrakestransactionDb, Transaction.class).build();
adapter = new FirebaseRecyclerAdapter<Transaction, TransactionViewHolder>(options) {
@Override
protected void onBindViewHolder(@NonNull TransactionViewHolder holder, int position, @NonNull Transaction model) {
holder.item_name_card.setText(model.getNameofitemstring());
holder.bought_by_card.setText(model.getBoughtbystring());
holder.bought_from_card.setText(model.getBoughtfromstring());
holder.date_card.setText(model.getDatestring());
holder.time_card.setText(model.getTimestring());
holder.cost_of_one_item_card.setText(model.getCostofoneitemstring());
holder.number_of_items_card.setText(model.getNumberofitemstring());
holder.total_cost_card.setText(model.getTotalcoststring());
}
@NonNull
@Override
public TransactionViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.transaction_row, parent, false);
return new TransactionViewHolder(itemView);
}
};
recyclerView.setAdapter(adapter);
}
@Override
protected void onStart() {
super.onStart();
adapter.startListening();
}
@Override
protected void onStop() {
super.onStop();
adapter.stopListening();
}
@Override
public boolean onContextItemSelected(@NonNull MenuItem item) {
if (item.getTitle().equals("Delete")) {
deleteTransaction(adapter.getRef(item.getOrder()).getKey());
}
return super.onContextItemSelected(item);
}
private void deleteTransaction(String key) {
BrakestransactionDb.child(key).removeValue();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.bottommenu, menu);
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(@NonNull MenuItem item) {
if (item.getItemId() == R.id.delete_all) {
BrakestransactionDb.removeValue();
}
if (item.getItemId() == R.id.home_button) {
Intent intent = new Intent(this, NavActivity.class);
finish();
startActivity(intent);
if (item.getItemId() == R.id.back_item_activity) {
Intent intent1 = new Intent(this, Department.class);
finish();
startActivity(intent1);
}
}
return super.onOptionsItemSelected(item);
}

}

---

这是我制作的型号类别-

package com.example.android.zfr.Model;
public class Transaction {
private String nameofitemstring,boughtbystring,boughtfromstring,costofoneitemstring,datestring,
timestring,totalcoststring,numberofitemstring;
public String getNameofitemstring() { return nameofitemstring; }
public void setNameofitemstring(String nameofitemstring) { this.nameofitemstring = nameofitemstring; }
public String getBoughtbystring() {return boughtbystring; }
public void setBoughtbystring(String bought string) {
this.boughtbystring = boughtbystring;
}
public String getBoughtfromstring() { return boughtfromstring; }
public void setBoughtfromstring(String boughtfromstring) { this.boughtfromstring = boughtfromstring; }
public String getCostofoneitemstring() {
return costofoneitemstring;
}
public void setCostofoneitemstring(String costofoneitemstring) { this.costofoneitemstring = costofoneitemstring; }
public String getDatestring() { return datestring; }
public void setDatestring(String datestring) { this.datestring = datestring; }
public String getTimestring() { return timestring; }
public void setTimestring(String timestring) { this.timestring = timestring; }
public String getTotalcoststring() { return totalcoststring; }
public void setTotalcoststring(String totalcoststring) { this.totalcoststring = totalcoststring; }
public String getNumberofitemstring() { return numberofitemstring; }
public void setNumberofitemstring(String numberofitemstring) { this.numberofitemstring = numberofitemstring; }
public Transaction() { }
public Transaction(String nameofitemstring,String boughtbystring,String boughtfromstring,String costofoneitemstring, String timestring,
String datestring ,String totalcoststring , String numberofitemstring ){
this.nameofitemstring=nameofitemstring;
this.boughtbystring=boughtbystring;
this.boughtfromstring=boughtfromstring;
this.costofoneitemstring=costofoneitemstring;
this.datestring=datestring;
this.timestring=timestring;
this.numberofitemstring=numberofitemstring;
this.totalcoststring=totalcoststring;
}

}

---

这是VIEWHOLDER类-

package com.example.android.zfr.ViewHolder;
import android.view.ContextMenu;
import android.view.View;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import com.example.android.zfr.R;
import com.facebook.shimmer.ShimmerFrameLayout;
public class TransactionViewHolder extends RecyclerView.ViewHolder implements 
View.OnCreateContextMenuListener{
public TextView item_name_card,bought_by_card,bought_from_card,date_card,
time_card,cost_of_one_item_card,number_of_items_card,total_cost_card;
public TransactionViewHolder(@NonNull View itemView) {
super(itemView);
item_name_card=itemView.findViewById(R.id.item_name_card);
bought_by_card=itemView.findViewById(R.id.bought_by_card);
bought_from_card=itemView.findViewById(R.id.bought_from_card);
date_card=itemView.findViewById(R.id.date_card);
time_card=itemView.findViewById(R.id.time_card);
cost_of_one_item_card=itemView.findViewById(R.id.cost_of_one_item_card);
number_of_items_card=itemView.findViewById(R.id.number_of_items_card);
total_cost_card=itemView.findViewById(R.id.total_cost_card);
itemView.setOnCreateContextMenuListener(this);
}
@Override
public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) 
{  menu.add(0,0,getAdapterPosition(),"Delete");  }
}

---

请帮忙。

Answer 1

您需要意识到Firebase是异步的，这意味着您的showTask((甚至在数据库能够向您发送数据之前就被调用了。为了避免这个问题，您需要将showTask((放入addValueEventListener中。试试这个：

BrakestransactionDb.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot ds : dataSnapshot.getChildren()) {
Map<String, Object> map = (Map<String, Object>) ds.getValue();
Object totalcost = map.get("totalcoststring");
int totalcostvalue = Integer.parseInt(String.valueOf(totalcost));
sumofbrakescost += totalcostvalue;
sumofbrakescostvalue = String.valueOf(sumofbrakescost);
}
brakesDb = database.getReference().child("Department").child("Brakes").child("Cost");
brakesDb.setValue(sumofbrakescostvalue);
showTask();
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});

Answer 2

它通过放置来工作

recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(BrakesItemActivity.this));

像这样的onDatachange方法：

BrakestransactionDb.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot ds : dataSnapshot.getChildren()) {
Map<String, Object> map = (Map<String, Object>) ds.getValue();
Object totalcost = map.get("totalcoststring");
int totalcostvalue = Integer.parseInt(String.valueOf(totalcost));
sumofbrakescost += totalcostvalue;
sumofbrakescostvalue = String.valueOf(sumofbrakescost);
}
brakesDb = database.getReference().child("Department").child("Brakes").child("Cost");
brakesDb.setValue(sumofbrakescostvalue);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(BrakesItemActivity.this));
}