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  2. Reading Firebase data and populating recyclerview

Reading Firebase data and populating recyclerview

由 社会主义新天地 提交于 2021-01-29 10:32:11

问题


I'm trying to read the data from Firebase and display it in a recyclerview with a card layout. I have a seperate activity for writing to Firebase and a fragment that actually displays the data in the app.

The app builds fine and runs, but crashes when I try to look at the fragment containing the recyclerView.

1) Fragment displays RecyclerView

package com.nikelspot.alpha;

import android.support.annotation.NonNull;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;

import com.google.firebase.auth.FirebaseAuth;
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;
import java.util.List;

import static android.content.ContentValues.TAG;

public class FragExplore extends Fragment {

    public FragExplore() {
        //required empty default constructor
    }

    public DatabaseReference comBaseRef;
    public FirebaseAuth mAuth;
    public List<ComicBase> list = new ArrayList<>();
    public RecyclerView recView;
    private RecyclerView.Adapter adapter;

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater,
                             ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.frag_explore,
                container, false);

        recView = rootView.findViewById(R.id.rec_view_buy);
        recView.setLayoutManager(new LinearLayoutManager(getActivity()));

        mAuth = FirebaseAuth.getInstance();
        comBaseRef = FirebaseDatabase.getInstance().getReference();

        comBaseRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                ComicBase comicBase = dataSnapshot.getValue(ComicBase.class);
                list.add(comicBase);

                adapter = new RecViewAdapter(getActivity(), list);
                recView.setAdapter(adapter);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
            }
        });
        return rootView;
    }
}

2) RecyclerViewAdapter java

package com.nikelspot.alpha;

import android.content.Context;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.List;

public class RecViewAdapter extends RecyclerView.Adapter<RecViewAdapter.ViewHolder> {

    public Context context;
    public List<ComicBase> list;

    public RecViewAdapter(Context context, List<ComicBase> List) {
        this.list = List;
        this.context = context;
    }

    // Create new views (invoked by the layout manager)
    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        // create a new view
        View comicView = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.recycler_items, null);

        // create ViewHolder
        ViewHolder viewHolder = new ViewHolder(comicView);
        return viewHolder;
    }

    // Replace the contents of a view (invoked by the layout manager)
    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        ComicBase comicBase = list.get(position);
        holder.comTitleHolder.setText(comicBase.getComTitle());
    }

    @Override
    public int getItemCount() {
        return list.size();
    }

    // inner class to hold a reference to each item of RecyclerView
    public class ViewHolder extends RecyclerView.ViewHolder {

        public TextView comTitleHolder;
        public ViewHolder(View comView) {
            super(comView);
            comTitleHolder = comView.findViewById(R.id.com_title);
        }
    }
}

3) Updated Getters/Setters java

package com.nikelspot.alpha;

public class ComicBase {

    private String comTitle, comIssue, comGrade, comPrice;

    public ComicBase(){
    //No-argument constructor
    //can leave empty
    }


    public ComicBase(String comTitle,
                     String comIssue,
                     String comGrade,
                     String comPrice){
        this.comTitle = comTitle;
        this.comIssue = comIssue;
        this.comGrade = comGrade;
        this.comPrice = comPrice;
    }

    public String getComTitle() {
        return comTitle;
    }

    public void setComTitle(String comTitle) {
        this.comTitle = comTitle;
    }

    public String getComIssue() {
        return comIssue;
    }

    public void getComIssue(String comIssue) {
        this.comIssue = comIssue;
    }

    public String getComGrade() {
        return comGrade;
    }

    public void setComGrade(String comGrade) {
        this.comGrade = comGrade;
    }

    public String getComPrice() {
        return comPrice;
    }

    public void setComPrice(String comPrice) {
        this.comPrice = comPrice;
    }
}

4) Card View XML

<?xml version="1.0" encoding="utf-8"?>

<android.support.v7.widget.CardView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/cardview1"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    card_view:cardElevation="5dp"
    card_view:contentPadding="5dp"
    card_view:cardCornerRadius="5dp"
    card_view:cardMaxElevation="5dp">

    <android.support.constraint.ConstraintLayout
        android:id="@+id/constraintLayout"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#ECEFF1"
        android:padding="10dp">

        <TextView
            android:id="@+id/com_title_show"
            android:layout_width="80dp"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:textColor="#000"
            android:textSize="20sp"
            card_view:layout_constraintBottom_toBottomOf="parent"
            card_view:layout_constraintEnd_toStartOf="@+id/com_issue_show"
            card_view:layout_constraintHorizontal_bias="0.5"
            card_view:layout_constraintStart_toStartOf="parent"
            card_view:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/com_issue_show"
            android:layout_width="80dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="8dp"
            android:textColor="#000"
            android:textSize="20sp"
            card_view:layout_constraintBottom_toBottomOf="parent"
            card_view:layout_constraintEnd_toStartOf="@+id/com_price_show"
            card_view:layout_constraintHorizontal_bias="0.5"
            card_view:layout_constraintStart_toEndOf="@+id/com_title_show"
            card_view:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/com_grade_show"
            android:layout_width="80dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="8dp"
            android:gravity="center"
            android:textColor="#000"
            android:textSize="20sp"
            card_view:layout_constraintBottom_toBottomOf="parent"
            card_view:layout_constraintEnd_toEndOf="parent"
            card_view:layout_constraintStart_toEndOf="@+id/com_price_show"
            card_view:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/com_price_show"
            android:layout_width="80dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="8dp"
            android:gravity="center"
            android:textColor="#000"
            android:textSize="20sp"
            card_view:layout_constraintBottom_toBottomOf="parent"
            card_view:layout_constraintEnd_toStartOf="@+id/com_grade_show"
            card_view:layout_constraintHorizontal_bias="0.5"
            card_view:layout_constraintStart_toEndOf="@+id/com_issue_show"
            card_view:layout_constraintTop_toTopOf="parent" />

    </android.support.constraint.ConstraintLayout>

</android.support.v7.widget.CardView>

5) Updated StackTrace

06-18 19:40:41.811 16590-16590/com.nikelspot.alpha E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.nikelspot.alpha, PID: 16590
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at com.nikelspot.alpha.RecViewAdapter.onBindViewHolder(RecViewAdapter.java:38)
    at com.nikelspot.alpha.RecViewAdapter.onBindViewHolder(RecViewAdapter.java:13)
    at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:6673)
    at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:6714)
    at android.support.v7.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:5647)
    at android.support.v7.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:5913)
    at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5752)
    at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5748)
    at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2232)
    at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1559)
    at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1519)
    at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:614)
    at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3812)
    at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:3225)
    at android.view.View.measure(View.java:22024)
    at android.support.constraint.ConstraintLayout.internalMeasureChildren(ConstraintLayout.java:1212)
    at android.support.constraint.ConstraintLayout.onMeasure(ConstraintLayout.java:1552)
    at android.view.View.measure(View.java:22024)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6584)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
    at android.view.View.measure(View.java:22024)
    at android.support.constraint.ConstraintLayout.internalMeasureChildren(ConstraintLayout.java:1212)
    at android.support.constraint.ConstraintLayout.onMeasure(ConstraintLayout.java:1552)
    at android.view.View.measure(View.java:22024)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6584)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
    at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:141)
    at android.view.View.measure(View.java:22024)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6584)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1514)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:806)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:685)
    at android.view.View.measure(View.java:22024)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6584)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
    at android.view.View.measure(View.java:22024)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6584)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1514)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:806)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:685)
    at android.view.View.measure(View.java:22024)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6584)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
    at com.android.internal.policy.DecorView.onMeasure(DecorView.java:746)
    at android.view.View.measure(View.java:22024)
    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2434)
    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1522)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1775)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1410)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6816)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:911)
06-18 19:40:41.812 16590-16590/com.nikelspot.alpha E/AndroidRuntime:     at android.view.Choreographer.doCallbacks(Choreographer.java:723)
    at android.view.Choreographer.doFrame(Choreographer.java:658)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:897)
    at android.os.Handler.handleCallback(Handler.java:789)
    at android.os.Handler.dispatchMessage(Handler.java:98)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6665)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:772)

回答1:


  1. In Your activity

public class ApprovedMeetingsActivity extends AppCompatActivity {

DatabaseReference rootRef, pendingMeetingsRef;
ListView pendingMeetingslist;
List<Meeting> meetings = new ArrayList<>();
MeetingsAdapter meetingsAdapter;

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

    pendingMeetingslist = findViewById(R.id.list);

    rootRef = FirebaseDatabase.getInstance().getReference();

    pendingMeetingsRef = rootRef.child("approved_meetings");

    loadListFromFirebase();
}

private void loadListFromFirebase() {

    pendingMeetingsRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                meetings.add(postSnapshot.getValue(Meeting.class));

                meetingsAdapter = new MeetingsAdapter(ApprovedMeetingsActivity.this, meetings, "startmeet");
                pendingMeetingslist.setAdapter(meetingsAdapter);

            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

}

  1. Getters and setters

public class Meeting {

String id;
String user;
String training;
String trainer;
String location;
String trainee;

public Meeting() {
    //Empty Constructor For Firebase
}


public void setallmeetings(String id, String user, String training, String trainer, String location)
{
    this.id = id;
    this.user = user; //Parameterized for Program-Inhouse objects.
    this.training = training;
    this.trainer = trainer;
    this.location = location;
}

//Getters and Setters
public String getId()
{
    return id;
}
public void setId(String id)
{
    this.id = id;
}
public String getUser()
{
    return user;
}
public void setUser(String user)
{
    this.user = user;
}
public String getTraining()
{
    return training;
}
public void setTraining(String training)
{
    this.training = training;
}
public String getTrainer()
{
    return trainer;
}
public void setTrainer(String trainer)
{
    this.trainer = trainer;
}
public String getLocation()
{
    return location;
}
public void setLocation(String location)
{
    this.location = location;
}
public String getTrainee()
{
    return trainee;
}
public void setTrainee(String trainee)
{
    this.trainee = trainee;
}
  1. Then finally in adapter set the data

public class MeetingsAdapter extends BaseAdapter {

private List<Meeting> listData;
private LayoutInflater layoutInflater;
Context context;
String text;
List<String> ids = new ArrayList<>();
DatabaseReference rootRef, pendingMeetingsRef, canceledMeetingsRef;

SendMsgViewModel sendMsgViewModel;
CompositeSubscription subscription = new CompositeSubscription();
Float lat , lng ;
Location currentLocation;
private SimpleLocation location;

public MeetingsAdapter(Context context, List<Meeting> listData, String text) {

    this.listData = listData;
    layoutInflater = LayoutInflater.from(context);
    this.context = context;
    this.text = text;
}

@Override
public int getCount() {
    return listData.size();
}

@Override
public Object getItem(int position) {
    return listData.get(position);
}

@Override
public long getItemId(int position) {
    return position;
}

@Override
public View getView(final int position, View convertView, ViewGroup parent) {
    ViewHolder holder;
    if (convertView == null) {
        convertView = layoutInflater.inflate(R.layout.item_meeting_list, null);
        holder = new ViewHolder();
        holder.meeting = convertView.findViewById(R.id.training_txt);
        holder.trainer = convertView.findViewById(R.id.trainer_txt);
        holder.location = convertView.findViewById(R.id.location_txt);
        holder.cancelMeetBtn = convertView.findViewById(R.id.cancel_meet_btn);
        holder.startMeetBtn = convertView.findViewById(R.id.start_meet_btn);

        if(text.equals("hidebtn")){
            holder.cancelMeetBtn.setVisibility(View.GONE);
            holder.startMeetBtn.setVisibility(View.GONE);
        }
        else if(text.equals("startmeet")){
            holder.cancelMeetBtn.setVisibility(View.GONE);
            holder.startMeetBtn.setVisibility(View.VISIBLE);
        }
        else {
            holder.cancelMeetBtn.setVisibility(View.VISIBLE);
            holder.startMeetBtn.setVisibility(View.GONE);
        }

        convertView.setTag(holder);
    } else {
        holder = (ViewHolder) convertView.getTag();
    }
    sendMsgViewModel = new SendMsgViewModel(new SendMsgInteractorImpl(), AndroidSchedulers.mainThread());
    location = new SimpleLocation(context);

    final PermissionListener permissionlistener = new PermissionListener() {
        @Override
        public void onPermissionGranted() {
            Toast.makeText(context, "Permission Granted", Toast.LENGTH_SHORT).show();

            NotifyData notifydata = new NotifyData(String.valueOf(location.getLatitude()),
                    String.valueOf(location.getLongitude()));

            subscription.add(sendMsgViewModel.sendMsg("key=AIzaSyCJT3Osi3pHf3K6nr_LRs1Xx0m0M5fID04",
                    new Message("cDjrAZSBTP4:APA91bG1hbHafiCuLRW_yy1OLbySkTXd0BPIvT5jA9xzZn4dW-4Cy0WRoqGKM9E6GSMumCd63Uu6xiksPYB1EmcOjn6v_jlZWsZ41I2z6laQtYlu7j57vimQVYOVXBNe1d8eBIqIZAfi",
                            notifydata,""))
                    .subscribeOn(Schedulers.io())
                    .observeOn(AndroidSchedulers.mainThread())
                    .subscribe(new Observer<Message>() {
                @Override
                public void onCompleted() {

                }

                @Override
                public void onError(Throwable e) {

                }

                @Override
                public void onNext(Message message) {

                }
            }));
        }

        @Override
        public void onPermissionDenied(ArrayList<String> deniedPermissions) {
            Toast.makeText(context, "Permission Denied\n" + deniedPermissions.toString(), Toast.LENGTH_SHORT).show();
        }


    };

    rootRef = FirebaseDatabase.getInstance().getReference();

    pendingMeetingsRef = rootRef.child("requested_meetings");
    canceledMeetingsRef = rootRef.child("canceled_meetings");

    for(int i=0; i < listData.size(); i++) {
        ids.add(listData.get(position).getId());
    }

    holder.meeting.setText(listData.get(position).getTraining());
    holder.trainer.setText(listData.get(position).getTrainer());
    holder.location.setText(listData.get(position).getLocation());

    holder.cancelMeetBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            new MaterialDialog.Builder(context)
                    .title("Cancel Meeting")
                    .backgroundColor(context.getResources().getColor(R.color.white))
                    .titleColor(context.getResources().getColor(R.color.black))
                    .contentColor(context.getResources().getColor(R.color.textColor))
                    .content("Are you sure you want to cancel this Meeting ?")
                    .positiveText("Yes")
                    .negativeText("No")
                    .onNegative(new MaterialDialog.SingleButtonCallback() {
                        @Override
                        public void onClick(@NonNull MaterialDialog dialog, @NonNull DialogAction which) {
                            dialog.dismiss();
                        }
                    })
                    .onPositive(new MaterialDialog.SingleButtonCallback() {
                        @Override
                        public void onClick(@NonNull MaterialDialog dialog, @NonNull DialogAction which) {
                            dialog.dismiss();

                            Meeting meet = new Meeting();
                            String id = canceledMeetingsRef.push().getKey();
                            meet.setId(id);
                            meet.setUser(listData.get(position).getUser());
                            meet.setTraining(listData.get(position).getTraining());
                            meet.setTrainer(listData.get(position).getTrainer());
                            meet.setLocation(listData.get(position).getLocation());
                            canceledMeetingsRef.child(id).setValue(meet);

                            listData.remove(position);

                            pendingMeetingsRef.child(ids.get(position)).removeValue();
                            ids.remove(position);
                            notifyDataSetChanged();
                            Toast.makeText(context,"Meeting successfully cancelled", Toast.LENGTH_SHORT).show();
                        }
                    })
                    .show();
        }
    });

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

            if (!location.hasLocationEnabled()) {
                // ask the user to enable location access
                SimpleLocation.openSettings(context);
                return;
            }

            new MaterialDialog.Builder(context)
                    .title("Start Meeting")
                    .backgroundColor(context.getResources().getColor(R.color.white))
                    .titleColor(context.getResources().getColor(R.color.black))
                    .contentColor(context.getResources().getColor(R.color.textColor))
                    .content("Are you sure you want to start this Meeting ?")
                    .positiveText("Yes")
                    .negativeText("No")
                    .onNegative(new MaterialDialog.SingleButtonCallback() {
                        @Override
                        public void onClick(@NonNull MaterialDialog dialog, @NonNull DialogAction which) {
                            dialog.dismiss();
                        }
                    })
                    .onPositive(new MaterialDialog.SingleButtonCallback() {
                        @Override
                        public void onClick(@NonNull MaterialDialog dialog, @NonNull DialogAction which) {
                            dialog.dismiss();

                            location.beginUpdates();

                            TedPermission.with(context)
                                    .setPermissionListener(permissionlistener)
                                    .setDeniedMessage("If you reject permission,you can not use this service\n\nPlease turn on permissions at [Setting] > [Permission]")
                                    .setPermissions(Manifest.permission.ACCESS_COARSE_LOCATION, Manifest.permission.ACCESS_FINE_LOCATION)
                                    .check();
                        }
                    })
                    .show();
        }


    });

    return convertView;
}

static class ViewHolder {
    TextView meeting, trainer, location;
    ImageView cancelMeetBtn;
    LinearLayout startMeetBtn;
}


void updateLocation(Location location) {
    currentLocation = location;
    lat = (float) currentLocation.getLatitude();
    lng = (float) currentLocation.getLongitude();
}

}



来源：https://stackoverflow.com/questions/50918372/reading-firebase-data-and-populating-recyclerview

标签
android
firebase
firebase-realtime-database
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