如何使用RecyclerView从Firebase获取密钥

Question

I can get key and show in Log.d but it don't show in RecyclerView. What's wrong with it?

HistoryActivity.java it contains my recyclerView:

public class HistoryActivity extends AppCompatActivity {

    FirebaseFirestore mFirestore;
    FirebaseAuth firebaseAuth;
    FirebaseDatabase database;

    RecyclerView mHisList;
    ArrayList<PreviousLst> history;
    adt_rv_HisList adtRvHisList;

    TextView ptName;
    TextView ptPort;

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

        getSupportActionBar().setSubtitle("History");

        Intent it = getIntent();
        String patName = it.getStringExtra("nm");
        String patID = it.getStringExtra("idpat");
        String portNum = it.getStringExtra("pNum");
        String regisDate = it.getStringExtra("rdate");

        ptName = findViewById(R.id.txName);
        ptPort = findViewById(R.id.portpassValue);

        ptName.setText(patName);
        ptPort.setText(portNum);

        history = new ArrayList<>();

        setupRecyclerView();
        setupFireBase();
        loadDataFromDatabase(portNum);

    }

    private void setupFireBase() {

        mFirestore = FirebaseFirestore.getInstance();
        firebaseAuth = FirebaseAuth.getInstance();
        database = FirebaseDatabase.getInstance();

    }

    private void setupRecyclerView() {
        mHisList = findViewById(R.id.rv_prev_lst);
        mHisList.setHasFixedSize(true);
        mHisList.setLayoutManager(new LinearLayoutManager(this));
        mHisList.setAdapter(adtRvHisList);
    }

    public void loadDataFromDatabase(String portNum) {
        if(history.size()>0)
            history.clear();

        DatabaseReference myRef;
        DatabaseReference passref;

        switch (portNum){

            case "Huang-Yai0002":
                String p2 = "NETEKG-Huang-Yai0002";
                myRef = database.getReference("MACHINE");
                passref = myRef.child(p2).child("value");

                passref.addValueEventListener(new ValueEventListener(){
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {

                        for (DataSnapshot postSnapshot: dataSnapshot.getChildren()) {

                            String keydate = postSnapshot.getKey();
                            Log.d(TAG, "Child are: " + keydate );
                            PreviousLst previousLst = new PreviousLst(keydate);
                            history.add(previousLst);
                        }
                        adtRvHisList = new adt_rv_HisList(HistoryActivity.this, history);
                        mHisList.setAdapter(adtRvHisList);
                    }
                    @Override
                    public void onCancelled(DatabaseError error) {
                        Log.w(TAG, "Failed to read value.", error.toException());
                    }
                });
                break;

            case "Huang-Yai0003":
                String p3 = "NETEKG-Huang-Yai0003";
                myRef = database.getReference("MACHINE");
                passref = myRef.child(p3).child("value");

                passref.addValueEventListener(new ValueEventListener(){
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {

                        for (DataSnapshot postSnapshot: dataSnapshot.getChildren()) {
                            String keydate = postSnapshot.getKey();
                            Log.d(TAG, "Child are: " + keydate );
                            PreviousLst previousLst = new PreviousLst(postSnapshot.getKey());
                            history.add(previousLst);
                        }
                        adtRvHisList = new adt_rv_HisList(HistoryActivity.this, history);
                        mHisList.setAdapter(adtRvHisList);
                    }
                    @Override
                    public void onCancelled(DatabaseError error) {

                        Log.w(TAG, "Failed to read value.", error.toException());
                    }
                });
                break;
            default:
                Log.d(TAG, "Value is: " + portNum);
                Toast.makeText(getApplicationContext(),"Error...",Toast.LENGTH_LONG).show();
                break;

        }
    }
}

adt_rv_HisList.java Adapter:

public class adt_rv_HisList extends RecyclerView.Adapter<adtrvHisListViewHolder> {
    HistoryActivity historyActivity;
    ArrayList<PreviousLst> history;


    public adt_rv_HisList(HistoryActivity historyActivity, ArrayList<PreviousLst> history) {
        this.history = history;
        this.historyActivity = historyActivity;
    }

    @NonNull
    @Override
    public adtrvHisListViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        View v = LayoutInflater.from(historyActivity.getBaseContext()).inflate(R.layout.hislist_item, viewGroup, false);
        return new adtrvHisListViewHolder(v);
    }

    @Override
    public void onBindViewHolder(@NonNull adtrvHisListViewHolder holder, int position) {

        holder.hdate.setText(history.get(position).getHisDate());

        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                dialogView();
            }
        });
    }

    private void dialogView() {
        final Dialog dia = new Dialog(historyActivity);
        dia.setContentView(R.layout.dialog_ask_view);
        dia.show();

        Button pvgraph = (Button)dia.findViewById(R.id.bt_pvgraph);
        Button pvhr = (Button)dia.findViewById(R.id.bt_pvhrate);
        Button cc = (Button)dia.findViewById(R.id.btn_cancel);

        cc.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                dia.dismiss();
            }
        });

        pvgraph.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                dia.dismiss();
                Intent it = new Intent(historyActivity, ViewgraphActivity.class);
                historyActivity.startActivity(it);
            }
        });

        pvhr.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                dia.dismiss();
                Intent it = new Intent(historyActivity, ViewHRActivity.class);
                historyActivity.startActivity(it);
            }
        });
    }

    @Override
    public int getItemCount() {
        return 0;
    }
}

adtrvHisListViewHolder.java Contains the ViewHolder :

public class adtrvHisListViewHolder extends RecyclerView.ViewHolder {

    public TextView hdate;

    public adtrvHisListViewHolder(View itemView) {
        super(itemView);

        hdate = itemView.findViewById(R.id.his_date);
    }
}

PreviousLst.java is Model class for my recyclerView:

public class PreviousLst {
    String HisDate;

    public PreviousLst(String HisDate){
        this.HisDate = HisDate;
    }

    public PreviousLst(){

    }

    public String getHisDate() {
        return HisDate;
    }
    public void setHisDate(String hisDate) {
        HisDate = hisDate;
    }
}

This is my key that I get and show in Log.d

• D/ContentValues: Child are: HEART RATE
• D/ContentValues: Child are:LEAD 1
• Child are: LEAD 2
• Child are: LEAD 3
• Child are: LEAD 4
• Child are: LEAD 5
• Child are: LEAD 6

but it don't shoe in App. enter image description here

Answer 1

@Override
public int getItemCount() {
    //return 0;
      replace it with history.size();
}

the added lines tells the adapter how many items, the adapter has to bind the items to the recycler view. By default it is 0, means the adapter class will never call the binView method to show the items at view side