Adding Cloud Firestore Documents Into an ArrayAdapter

问题

Im trying to add cloud database Documents into an ArrayAdapter for my card stack. I have the Collection "Users" and Document "userID" which contains the users name and gender. Im trying to add the users name to a card stack. So far Iv been able to add the users to a list but cannot get them into my cards.

When I run the app I get this error: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference

This error occurs at Name_On_Card.setText(strangers); in the CardAdapter.java Ill add the code to my CardAdapter and MainActivity Im using

Model.java

public class Model {
  public String name_on_card;
  public ImageView card_image;

public Model(TextView name_on_card, ImageView card_image) {
}
public String getName_on_card() {
    return name_on_card;
}
public void setName_on_card(String name_on_card) {
    this.name_on_card = name_on_card;
}
public ImageView getCard_image() {
    return card_image;
}

public void setCard_image(ImageView card_image) {
    this.card_image = card_image;
}}

CardAdapter.java

public class CardAdpater extends BaseCardAdapter {
private List<Model> modelList;
private Context context;

public CardAdpater(List<Model> modelList, Context context) {
    this.modelList = modelList;
    this.context = context;
}
@Override
public int getCount() {
    return modelList.size();
}
@Override
public int getCardLayoutId() {
    return R.layout.card_item;
}
@Override
public void onBindData(int position, View cardview) {
    if (modelList == null || modelList.size() == 0);
    {
        ImageView imageView = cardview.findViewById(R.id.card_image);
        TextView textView = cardview.findViewById(R.id.name_on_card);
        Model model = modelList.get(position);
        textView.setText(model.getName_on_card());
        imageView.setImageResource(R.drawable.ic_launcher_background);
    }}}

MainActivity.java

public class MainActivity extends AppCompatActivity {
public static final String TAG = MainActivity.class.getSimpleName();
TextView Name_On_Card;
FirebaseAuth mAuth;
FirebaseFirestore dataBase;
String userID;
ImageView Image_On_Card;
private SwipeCardsView swipeCardsView;
private List<Model> modelList = new ArrayList<>();

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

    mAuth = FirebaseAuth.getInstance();
    dataBase = FirebaseFirestore.getInstance();
    userID = mAuth.getCurrentUser().getUid();
    Image_On_Card = findViewById(R.id.card_image);
    Name_On_Card = findViewById(R.id.name_on_card);

    //SwipeCards
    swipeCardsView = findViewById(R.id.swipeCardsView);
    swipeCardsView.retainLastCard(false);
    swipeCardsView.enableSwipe(true);

    getUserDB();
    getData();
    }
    // Method for getting Users from database
    private void getUserDB () {
        dataBase.collection("Users").get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
            @Override
            public void onComplete(@NonNull Task<QuerySnapshot> task) {
                if (task.isSuccessful()) {
                    List<String> list = new ArrayList<>();
                    for (QueryDocumentSnapshot document : task.getResult()) {
                        list.add(document.getString("Name"));
                    }
                    Log.d(TAG, list.toString());

                    String strangers = list.toString();
                    Name_On_Card.setText(strangers);

                } else {
                    Log.d(TAG, "Error getting documents: ", task.getException());
                }
            }});
        }
    // CardAdpater method
     private void getData() {
       modelList.add(new Model(Name_On_Card,Image_On_Card));
          CardAdpater cardAdpater = new CardAdpater(modelList,this);
         swipeCardsView.setAdapter(cardAdpater);
      }
    //LogOut OnClick
    public void LogOut(View view) {
    FirebaseAuth.getInstance().signOut();
    startActivity(new Intent(getApplicationContext(), Login.class));
    finish();
    }
    private class CardStackTransformer implements ViewPager.PageTransformer {
        @Override
        public void transformPage(@NonNull View page, float position) {
        }}}

card_item.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">

<RelativeLayout
   android:layout_width="match_parent"
   android:layout_height="match_parent">

   <ImageView
       android:id="@+id/card_image"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       android:src="@mipmap/ic_launcher_round"
        />
   <TextView
       android:id="@+id/name_on_card"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:layout_alignParentBottom="true"
       android:layout_centerHorizontal="true"
       android:gravity="center"
       android:paddingBottom="55dp"
       android:text="Name Holder">
   </TextView>
</RelativeLayout>

来源：https://stackoverflow.com/questions/60081740/adding-cloud-firestore-documents-into-an-arrayadapter