为什么我的 onBindViewHolder () 根本没有运行，即使我的所有其他回收器视图方法都运行了？

Question

I have created a recycler view that is supposed to display data in a text view and an image view. But the onBindViewHolder () for my adapter does not run. All the other methods in my adapter run. I cannot find the reason why the onBindViewHolder () does not run, everything else seems to be working fine it's just my data is not displayed in the card views for my recycler view. Any help would be appreciated thanks.

Adapter code:

package com.myapps.myapplication;

import android.content.Context;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import androidx.recyclerview.widget.RecyclerView;
import androidx.cardview.widget.CardView;

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

private Context context;
private Cursor cursor;

public captionedImagesAdapter (Context context, Cursor cursor) {
    this.context = context;
    this.cursor = cursor;
}

public captionedImagesAdapter.ViewHolder onCreateViewHolder (ViewGroup parent, int viewType) {
    LayoutInflater inflater = LayoutInflater.from(context);
    CardView cv = (CardView) inflater.inflate(R.layout.card_view, parent, false);

    return new ViewHolder (cv);
}

public void onBindViewHolder(ViewHolder holder, int position) {
    if (cursor.moveToPosition(position)) {
        return;
    }

    String info_text = cursor.getString (0);
    byte [] info_image = cursor.getBlob(1);

    Bitmap bitmap = MyDatabaseHelper.getImages(info_image);

    holder.textView.setText(info_text);
    holder.imageView.setImageBitmap(bitmap);
}

public int getItemCount() {
    return cursor.getCount();
}

public static class ViewHolder extends RecyclerView.ViewHolder {
    private ImageView imageView;
    private TextView textView;

    public ViewHolder(CardView view) {
        super(view);
        imageView = view.findViewById(R.id.info_image);
        textView = view.findViewById(R.id.info_text);
    }
}

}

Database code:

package com.myapps.myapplication;

import android.content.ContentValues;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Log;

import java.io.ByteArrayOutputStream;
import java.util.ArrayList;

public class MyDatabaseHelper extends SQLiteOpenHelper {

private static final String DB_NAME = "starbuzz";
private static final int DB_VERSION = 5;
private Context context;
private ArrayList <Bitmap> bitmapArray;
private byte [] byteArray;

public MyDatabaseHelper(Context context) {
    super(context, DB_NAME, null, DB_VERSION);
    this.context = context;
}

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL("CREATE TABLE GROCERY_ITEMS (" + "_id INTEGER PRIMARY KEY AUTOINCREMENT, " + "NAME TEXT, " + "IMAGE_RESOURCE_ID BLOB);");

    upgradeDatabase(db);
}

public void upgradeDatabase (SQLiteDatabase db) {
    convertToBitmap();
    byteArray = convertToByte();
    addItems(db);
}

public void convertToBitmap () {
    Bitmap faan = BitmapFactory.decodeResource(context.getResources(), R.drawable.faan);
    Bitmap milk = BitmapFactory.decodeResource (context.getResources(), R.drawable.milk);
    Bitmap egg = BitmapFactory.decodeResource (context.getResources(), R.drawable.egg);
    Bitmap toilet_tissue = BitmapFactory.decodeResource (context.getResources(), R.drawable.toilet_tissue);
    Bitmap kitchen_tissue = BitmapFactory.decodeResource (context.getResources(), R.drawable.kitchen_tissue);
    Bitmap bread = BitmapFactory.decodeResource (context.getResources(), R.drawable.bread);
    Bitmap potatoe = BitmapFactory.decodeResource (context.getResources(), R.drawable.potatoe);
    Bitmap onion = BitmapFactory.decodeResource (context.getResources(), R.drawable.onion);
    Bitmap flour = BitmapFactory.decodeResource (context.getResources(), R.drawable.flour);
    Bitmap tomatoe = BitmapFactory.decodeResource (context.getResources(), R.drawable.tomatoe);
    Bitmap corriandor = BitmapFactory.decodeResource (context.getResources(), R.drawable.corriandor);

    bitmapArray = new ArrayList <Bitmap> ();

    bitmapArray.add(faan);
    bitmapArray.add (milk);
    bitmapArray.add (egg);
    bitmapArray.add (toilet_tissue);
    bitmapArray.add (kitchen_tissue);
    bitmapArray.add (bread);
    bitmapArray.add (potatoe);
    bitmapArray.add (onion);
    bitmapArray.add (flour);
    bitmapArray.add (tomatoe);
    bitmapArray.add (corriandor);

}

public byte [] convertToByte () {

    ByteArrayOutputStream stream = new ByteArrayOutputStream ();

    for (Bitmap bitmap : bitmapArray) {
        bitmap.compress (Bitmap.CompressFormat.PNG, 0, stream);
    }

    return stream.toByteArray();
}

public static Bitmap getImages (byte [] image) {
    return BitmapFactory.decodeByteArray(image, 0, image.length);
}

public void addItems (SQLiteDatabase db) {

    byte faan = byteArray [0];
    byte milk = byteArray [1];
    byte egg = byteArray [2];
    byte toilet_tissue = byteArray [3];
    byte kitchen_tissue = byteArray [4];
    byte bread = byteArray [5];
    byte potatoe = byteArray [6];
    byte onion = byteArray [7];
    byte flour = byteArray [8];
    byte tomatoe = byteArray [9];
    byte corriandor = byteArray [10];

    insertItems (db, "Faan", faan);
    insertItems (db, "Milk", milk);
    insertItems (db, "Egg", egg);
    insertItems (db, "Toilet Tissue", toilet_tissue);
    insertItems (db, "Kitchen Tissue", kitchen_tissue);
    insertItems (db, "Bread", bread);
    insertItems (db, "Potatoe", potatoe);
    insertItems (db, "Onion", onion);
    insertItems (db, "Flour", flour);
    insertItems (db, "Tomatoe", tomatoe);
    insertItems (db, "Corriandor", corriandor);

}

public void insertItems (SQLiteDatabase db, String name, byte image) {
    ContentValues contentValues = new ContentValues();
    contentValues.put ("NAME", name);
    contentValues.put ("IMAGE_RESOURCE_ID", image);

    db.insert ("GROCERY_ITEMS", null, contentValues);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("CREATE TABLE GROCERY_ITEMS (" + "_id INTEGER PRIMARY KEY AUTOINCREMENT, " + "NAME TEXT, " + "IMAGE_RESOURCE_ID BLOB);");

    upgradeDatabase(db);
}
}

RecyclerView code:

package com.myapps.myapplication;

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.GridLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

public class grocery_item extends AppCompatActivity {

SQLiteDatabase db;
Cursor cursor;

protected void onCreate (Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.item_grocery);

    accessDataBase();

    RecyclerView groceryRecycler = (RecyclerView) findViewById(R.id.grocery_recycler_view);

    captionedImagesAdapter adapter = new captionedImagesAdapter (this, cursor);
    GridLayoutManager layoutManager = new GridLayoutManager(this, 2, GridLayoutManager.VERTICAL, false);
    groceryRecycler.setLayoutManager(layoutManager);
    groceryRecycler.setAdapter (adapter);
}

public void accessDataBase () {
    MyDatabaseHelper databaseHelper = new MyDatabaseHelper(this);

    try {

        db = databaseHelper.getReadableDatabase();

        cursor = db.query ("GROCERY_ITEMS", new String[] {"NAME", "IMAGE_RESOURCE_ID"}, null, null, null, null, null);

    } catch (SQLiteException e) {
        e.printStackTrace();
    }
}
}

Answer 1

You're returning from onBindViewHolder() immediately:

 if (cursor.moveToPosition(position)) { return; }

moveToPosition() returns true on success.