Android RecyclerView + CursorLoader + ContentProvider + "Load More"

Question

I have created one Activity in that I am implementing CursorLoader for load data from Database.

I have done that thing for all records of that Table but I want to load 30-30 records like Load More Functionality

I have tried to create query and its loading first 30 records but I cant able to understand how can I request for new records.

My Activity Code is Like:

public class ProductListActivity extends AppCompatActivity         implements LoaderManager.LoaderCallbacks<Cursor> {      /**      * Records in list      */     int offset = 0;      /**      * For Current Activity *      */     Context mContext;      /**      * Activity Binding      */     ActivityProductListBinding activityProductListBinding;      /**      * Product Adapter      */     ProductListAdapter productListAdapter;      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);          /**          * DataBinding with XML          */         activityProductListBinding = DataBindingUtil.setContentView(this, R.layout.activity_product_list);          /**          * Getting Context          */         mContext = getApplicationContext();          /***          * TOOLBAR Settings...          */         setSupportActionBar(activityProductListBinding.toolbar);         activityProductListBinding.toolbarTitleTextview.setText(R.string.string_title_products);         getSupportActionBar().setDisplayHomeAsUpEnabled(true);         getSupportActionBar().setDisplayShowTitleEnabled(false);          final ActionBar ab = getSupportActionBar();         if (ab != null)             ab.setDisplayHomeAsUpEnabled(true);          /**          * RecyclerView Setup          */         GridLayoutManager manager = new GridLayoutManager(this, 2);         activityProductListBinding.productListRecyclerView.setLayoutManager(manager);          /**          * First Time init Loader          */         getSupportLoaderManager().initLoader(1, null, this);     }      @Override     public Loader<Cursor> onCreateLoader(int id, Bundle args) {         final Uri CONTENT_URI = KOOPSContentProvider.CONTENT_URI_PRODUCT.buildUpon()                 .appendQueryParameter(KOOPSContentProvider.QUERY_PARAMETER_OFFSET,                         String.valueOf(offset))                 .build();         return new CursorLoader(this, CONTENT_URI ,null, null, null, null);     }      @Override     public void onLoadFinished(Loader<Cursor> loader, Cursor data) {         //When the loader has loaded some data (either initially, or the         //datasource has changed and a new cursor is being provided),         //Then we'll swap out the cursor in our recyclerview's adapter         // and we'll create the adapter if necessary         Log.d(LogUtils.TAG, "Cursor : " + data.getCount());         if (productListAdapter == null) {             productListAdapter = new ProductListAdapter(this, data);             activityProductListBinding.productListRecyclerView.setAdapter(productListAdapter);         }     }      @Override     public void onLoaderReset(Loader<Cursor> loader) {         //If the loader is reset, we need to clear out the         //current cursor from the adapter.         productListAdapter.reQuery(null);     } } 

UPDATE:

I have added EndlessRecyclerViewScrollListener

activityProductListBinding.productListRecyclerView.addOnScrollListener(new EndlessRecyclerViewScrollListener(manager) {             @Override             public void onLoadMore(int page, int totalItemsCount) {                 // Triggered only when new data needs to be appended to the list                 // Add whatever code is needed to append new items to the bottom of the list                 offset = limit * page;                 /**                  * Adding Bundle in Loader and then Call                  */                 getSupportLoaderManager().initLoader(LOADER_ID, productQueryData, ProductListActivity.this);             }         }); 

I have tried to MergeCursor in adapter but getting error:

FATAL EXCEPTION: main  Process: com.kevalam.koopsv3, PID: 25021  java.lang.IllegalStateException: Observer android.database.MergeCursor$1@570f82d is already registered.     at android.database.Observable.registerObserver(Observable.java:49)     at android.database.AbstractCursor.registerDataSetObserver(AbstractCursor.java:358)     at android.database.CursorWrapper.registerDataSetObserver(CursorWrapper.java:222)     at android.database.MergeCursor.<init>(MergeCursor.java:50)     at com.kevalam.koops.adapter.ProductListAdapter.mergeCursor(ProductListAdapter.java:71)     at com.kevalam.koops.ui.ProductListActivity.onLoadFinished(ProductListActivity.java:161)     at com.kevalam.koops.ui.ProductListActivity.onLoadFinished(ProductListActivity.java:38) 

Edited (ADAPTER Code):

public class ProductListAdapter extends RecyclerView.Adapter<ProductListAdapter.ViewHolder> {      // Because RecyclerView.Adapter in its current form doesn't natively      // support cursors, we wrap a CursorAdapter that will do all the job     // for us.     CursorAdapter mCursorAdapter;      Activity mContext;     Random rnd;      public ProductListAdapter(AppCompatActivity context, Cursor c) {          mContext = context;         rnd = new Random();          mCursorAdapter = new CursorAdapter(mContext, c, 0) {              @Override             public View newView(Context context, Cursor cursor, ViewGroup parent) {                 // Inflate the view here                 LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);                 return inflater.inflate(R.layout.row_product_layout_grid, parent, false);             }              @Override             public void bindView(View view, Context context, Cursor cursor) {                 String productName = cursor.getString(cursor.getColumnIndex(PRODUCT_NAME));                  // Binding operations                 ((TextView) view.findViewById(R.id.sub_product_name_text_view)).setText(productName);                  int color = Color.argb(200, rnd.nextInt(256), rnd.nextInt(256), rnd.nextInt(256));                  String url = "http://dummyimage.com/300/" + color + "/ffffff&text=" + (cursor.getPosition() + 1);                  Picasso                         .with(context)                         .load(url)                         .placeholder(R.mipmap.ic_launcher) // can also be a drawable                         .into((ImageView) view.findViewById(R.id.sub_product_image_view));             }         };     }      public void mergeCursor(Cursor c) {         if (mCursorAdapter != null) {             Cursor[] cursorArray = {mCursorAdapter.getCursor(), c};             MergeCursor mergeCursor = new MergeCursor(cursorArray);             reQuery(mergeCursor);         }     }      public void reQuery(Cursor c) {         if (mCursorAdapter != null) {             mCursorAdapter.changeCursor(c);             mCursorAdapter.notifyDataSetChanged();             notifyDataSetChanged();         }     }      @Override     public int getItemCount() {         return mCursorAdapter.getCount();     }      @Override     public void onBindViewHolder(ViewHolder holder, int position) {         // Passing the binding operation to cursor loader         mCursorAdapter.getCursor().moveToPosition(position); //EDITED: added this line as suggested in the comments below, thanks :)         mCursorAdapter.bindView(holder.view, mContext, mCursorAdapter.getCursor());     }      @Override     public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {         // Passing the inflater job to the cursor-adapter         View v = mCursorAdapter.newView(mContext, mCursorAdapter.getCursor(), parent);         return new ViewHolder(v);     }      public static class ViewHolder extends RecyclerView.ViewHolder {         View view;          public ViewHolder(View itemView) {             super(itemView);             view = itemView.findViewById(R.id.product_row_card_view);         }     } } 

Anybody can help please, Thanks in advance.

Answer 1

Update 01.10.2017 Google announced new library for paging, more info here https://developer.android.com/topic/libraries/architecture/paging.html

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Here is working sample with pagination based on cursoradapter+recyclerview+provider.

I give you step by step with code + bonus with gif preview.

But IMHO pagination on cursor adapter has nonsense because db is handling all heavy stuff with load more data :)

Step 1. create database:

public class CustomSqliteOpenHelper extends SQLiteOpenHelper {      private static final String TAG = "CustomSqliteOpenHelper";      public CustomSqliteOpenHelper(Context context) {         super(context, "db.db", null, 1);     }      @Override     public void onOpen(SQLiteDatabase db) {         super.onOpen(db);     }      @Override     public void onCreate(SQLiteDatabase db) {         db.execSQL(TableItems.CREATE_TABLE);     }      @Override     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {         db.execSQL(TableItems.DROP_TABLE);         onCreate(db);     }  } 

Step 2. create table

public class TableItems {     public static final String NAME = TableItems.class.getSimpleName().toLowerCase();     public static final String _ID = "_id";     public static final String TEXT = "text";      public static final String CREATE_TABLE =             "CREATE TABLE " + NAME +                     " ( " +                     _ID + " integer primary key autoincrement, " +                     TEXT + " text " +                     " ); ";      public static final String DROP_TABLE = "DROP TABLE IF EXISTS " + NAME;     public static String[] Columns = new String[]{_ID, TEXT}; } 

Step 3. create provider

import android.content.ContentProvider; import android.content.ContentUris; import android.content.ContentValues; import android.content.UriMatcher; import android.database.Cursor; import android.database.SQLException; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.database.sqlite.SQLiteQueryBuilder; import android.net.Uri; import android.support.annotation.NonNull; import android.util.Log;  import com.example.pagingproject.BuildConfig;  public class RequestProvider extends ContentProvider {     private static final String TAG = "RequestProvider";      private SQLiteOpenHelper mSqliteOpenHelper;     private static final UriMatcher sUriMatcher;      public static final String AUTHORITY = BuildConfig.APPLICATION_ID + ".db";      private static final int             TABLE_ITEMS = 0;      static {         sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);         sUriMatcher.addURI(AUTHORITY, TableItems.NAME + "/offset/" + "#", TABLE_ITEMS);     }      public static Uri urlForItems(int limit) {         return Uri.parse("content://" + AUTHORITY + "/" + TableItems.NAME + "/offset/" + limit);     }      @Override     public boolean onCreate() {         mSqliteOpenHelper = new CustomSqliteOpenHelper(getContext());         return true;     }      @Override     synchronized public Cursor query(@NonNull Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {          SQLiteDatabase db = mSqliteOpenHelper.getReadableDatabase();         SQLiteQueryBuilder sqb = new SQLiteQueryBuilder();         Cursor c = null;         String offset;          switch (sUriMatcher.match(uri)) {             case TABLE_ITEMS: {                 sqb.setTables(TableItems.NAME);                 offset = uri.getLastPathSegment();                 break;             }              default:                 throw new IllegalArgumentException("uri not recognized!");         }          int intOffset = Integer.parseInt(offset);          String limitArg = intOffset + ", " + 30;         Log.d(TAG, "query: " + limitArg);         c = sqb.query(db, projection, selection, selectionArgs, null, null, sortOrder, limitArg);          c.setNotificationUri(getContext().getContentResolver(), uri);          return c;     }      @Override     public String getType(@NonNull Uri uri) {         return BuildConfig.APPLICATION_ID + ".item";     }      @Override     public Uri insert(@NonNull Uri uri, ContentValues values) {         String table = "";         switch (sUriMatcher.match(uri)) {             case TABLE_ITEMS: {                 table = TableItems.NAME;                 break;             }         }          long result = mSqliteOpenHelper.getWritableDatabase().insertWithOnConflict(table, null, values, SQLiteDatabase.CONFLICT_IGNORE);          if (result == -1) {             throw new SQLException("insert with conflict!");         }          Uri retUri = ContentUris.withAppendedId(uri, result);         return retUri;     }      @Override     public int delete(@NonNull Uri uri, String selection, String[] selectionArgs) {         return -1;     }      @Override     public int update(@NonNull Uri uri, ContentValues values, String selection, String[] selectionArgs) {         return -1;     } } 

Step 4. create an abstract cursor adapters, I took sample from StackOverflow custom-cursor-recyclerView-adapter

import android.content.Context; import android.database.Cursor; import android.database.DataSetObserver; import android.support.v7.widget.RecyclerView; import android.view.ViewGroup;  /**  * Created by skyfishjy on 10/31/14.  */  public abstract class CursorRecyclerViewAdapter<VH extends RecyclerView.ViewHolder> extends RecyclerView.Adapter<VH> {      protected Context mContext;      private Cursor mCursor;      private boolean mDataValid;      private int mRowIdColumn;      private DataSetObserver mDataSetObserver;      public CursorRecyclerViewAdapter(Context context, Cursor cursor) {         mContext = context;         mCursor = cursor;         mDataValid = cursor != null;         mRowIdColumn = mDataValid ? mCursor.getColumnIndex("_id") : -1;         mDataSetObserver = new NotifyingDataSetObserver(this);         if (mCursor != null) {             mCursor.registerDataSetObserver(mDataSetObserver);         }     }      public Cursor getCursor() {         return mCursor;     }      @Override     public int getItemCount() {         if (mDataValid && mCursor != null) {             return mCursor.getCount();         }         return 0;     }      @Override     public long getItemId(int position) {         if (mDataValid && mCursor != null && mCursor.moveToPosition(position)) {             return mCursor.getLong(mRowIdColumn);         }         return 0;     }      @Override     public void setHasStableIds(boolean hasStableIds) {         super.setHasStableIds(true);     }      public static final String TAG = CursorRecyclerViewAdapter.class.getSimpleName();      public abstract void onBindViewHolder(VH viewHolder, Cursor cursor);      @Override     public VH onCreateViewHolder(ViewGroup parent, int viewType) {         return null;     }      @Override     public void onBindViewHolder(VH viewHolder, int position) {         if (!mDataValid) {             throw new IllegalStateException("this should only be called when the cursor is valid");         }         if (!mCursor.moveToPosition(position)) {             throw new IllegalStateException("couldn't move cursor to position " + position);         }         onBindViewHolder(viewHolder, mCursor);     }      /**      * Change the underlying cursor to a new cursor. If there is an existing cursor it will be      * closed.      */     public void changeCursor(Cursor cursor) {         Cursor old = swapCursor(cursor);         if (old != null) {             old.close();         }     }      /**      * Swap in a new Cursor, returning the old Cursor.  Unlike      * {@link #changeCursor(Cursor)}, the returned old Cursor is <em>not</em>      * closed.      */     public Cursor swapCursor(Cursor newCursor) {         if (newCursor == mCursor) {             return null;         }         final Cursor oldCursor = mCursor;         if (oldCursor != null && mDataSetObserver != null) {             oldCursor.unregisterDataSetObserver(mDataSetObserver);         }         mCursor = newCursor;         if (mCursor != null) {             if (mDataSetObserver != null) {                 mCursor.registerDataSetObserver(mDataSetObserver);             }             mRowIdColumn = newCursor.getColumnIndexOrThrow("_id");             mDataValid = true;             notifyDataSetChanged();         } else {             mRowIdColumn = -1;             mDataValid = false;             notifyDataSetChanged();             //There is no notifyDataSetInvalidated() method in RecyclerView.Adapter         }         return oldCursor;     }      public void setDataValid(boolean mDataValid) {         this.mDataValid = mDataValid;     }      private class NotifyingDataSetObserver extends DataSetObserver {         private RecyclerView.Adapter adapter;          public NotifyingDataSetObserver(RecyclerView.Adapter adapter) {             this.adapter = adapter;         }          @Override         public void onChanged() {             super.onChanged();             ((CursorRecyclerViewAdapter) adapter).setDataValid(true);             adapter.notifyDataSetChanged();         }          @Override         public void onInvalidated() {             super.onInvalidated();             ((CursorRecyclerViewAdapter) adapter).setDataValid(false);         }     } } 

Step 5. create your own adapter with extending(inheriting) previous class

import android.content.Context; import android.database.Cursor; import android.support.v7.widget.RecyclerView; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup;  /**  * Created by deadfish on 2016-01-28.  */ public class CustomCursorRecyclerViewAdapter extends CursorRecyclerViewAdapter {      public CustomCursorRecyclerViewAdapter(Context context, Cursor cursor) {         super(context, cursor);     }      @Override     public long getItemId(int position) {         return super.getItemId(position);     }      @Override     public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {         View v = LayoutInflater.from(mContext).inflate(android.R.layout.simple_list_item_1, parent, false);         return new CustomViewHolder(v);     }      @Override     public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, Cursor cursor) {         CustomViewHolder holder = (CustomViewHolder) viewHolder;         cursor.moveToPosition(cursor.getPosition());         holder.setData(cursor);     }      @Override     public int getItemCount() {         return super.getItemCount();     }      @Override     public int getItemViewType(int position) {         return 0;     } } 

Step 6. create custom viewHolder

import android.database.Cursor; import android.support.v7.widget.RecyclerView; import android.view.View; import android.widget.TextView;  public class CustomViewHolder extends RecyclerView.ViewHolder {      public TextView textView1;      public CustomViewHolder(View itemView) {         super(itemView);         textView1 = (TextView) itemView.findViewById(android.R.id.text1);     }      public void setData(Cursor c) {         textView1.setText(c.getString(c.getColumnIndex("text")));     } } 

Step 7. write code in sample MainActivity

import android.content.ContentValues; import android.database.Cursor; import android.database.MatrixCursor; import android.os.Bundle; import android.os.Handler; import android.support.v4.app.LoaderManager; import android.support.v4.content.CursorLoader; import android.support.v4.content.Loader; import android.support.v7.app.AppCompatActivity; import android.support.v7.widget.LinearLayoutManager; import android.support.v7.widget.RecyclerView; import android.util.Log; import android.widget.Toast;  import com.example.pagingproject.adapters.CustomCursorRecyclerViewAdapter; import com.example.pagingproject.databases.RequestProvider; import com.example.pagingproject.databases.TableItems;  public class MainActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<Cursor> {      public final int offset = 30;     private int page = 0;      private RecyclerView mRecyclerView;     private boolean loadingMore = false;     private Toast shortToast;      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);          LinearLayoutManager mLayoutManager = new LinearLayoutManager(this);         CustomCursorRecyclerViewAdapter mAdapter = new CustomCursorRecyclerViewAdapter(this, null);          mRecyclerView = (RecyclerView) findViewById(R.id.recyclerView);         mRecyclerView.setLayoutManager(mLayoutManager);         mRecyclerView.setAdapter(mAdapter);          int itemsCountLocal = getItemsCountLocal();         if (itemsCountLocal == 0) {             fillTestElements();         }          shortToast = Toast.makeText(this, "", Toast.LENGTH_SHORT);          mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {             @Override             public void onScrolled(RecyclerView recyclerView, int dx, int dy) {                 super.onScrolled(recyclerView, dx, dy);                  LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();                 int lastVisibleItemPosition = layoutManager.findLastVisibleItemPosition();                 int maxPositions = layoutManager.getItemCount();                  if (lastVisibleItemPosition == maxPositions - 1) {                     if (loadingMore)                         return;                      loadingMore = true;                     page++;                     getSupportLoaderManager().restartLoader(0, null, MainActivity.this);                 }             }         });          getSupportLoaderManager().restartLoader(0, null, this);     }      private void fillTestElements() {         int size = 1000;         ContentValues[] cvArray = new ContentValues[size];         for (int i = 0; i < cvArray.length; i++) {             ContentValues cv = new ContentValues();             cv.put(TableItems.TEXT, ("text " + i));             cvArray[i] = cv;         }          getContentResolver().bulkInsert(RequestProvider.urlForItems(0), cvArray);     }      private int getItemsCountLocal() {         int itemsCount = 0;          Cursor query = getContentResolver().query(RequestProvider.urlForItems(0), null, null, null, null);         if (query != null) {             itemsCount = query.getCount();             query.close();         }         return itemsCount;     }      /*loader*/      @Override     public Loader<Cursor> onCreateLoader(int id, Bundle args) {         switch (id) {             case 0:                 return new CursorLoader(this, RequestProvider.urlForItems(offset * page), null, null, null, null);             default:                 throw new IllegalArgumentException("no id handled!");         }     }      @Override     public void onLoadFinished(Loader<Cursor> loader, Cursor data) {         switch (loader.getId()) {             case 0:                 Log.d(TAG, "onLoadFinished: loading MORE");                 shortToast.setText("loading MORE " + page);                 shortToast.show();                  Cursor cursor = ((CustomCursorRecyclerViewAdapter) mRecyclerView.getAdapter()).getCursor();                  //fill all exisitng in adapter                 MatrixCursor mx = new MatrixCursor(TableItems.Columns);                 fillMx(cursor, mx);                  //fill with additional result                 fillMx(data, mx);                  ((CustomCursorRecyclerViewAdapter) mRecyclerView.getAdapter()).swapCursor(mx);                   handlerToWait.postDelayed(new Runnable() {                     @Override                     public void run() {                         loadingMore = false;                     }                 }, 2000);                  break;             default:                 throw new IllegalArgumentException("no loader id handled!");         }     }      private Handler handlerToWait = new Handler();      private void fillMx(Cursor data, MatrixCursor mx) {         if (data == null)             return;          data.moveToPosition(-1);         while (data.moveToNext()) {             mx.addRow(new Object[]{                     data.getString(data.getColumnIndex(TableItems._ID)),                     data.getString(data.getColumnIndex(TableItems.TEXT))             });         }     }      @Override     public void onLoaderReset(Loader<Cursor> loader) {         // TODO: 2016-10-13     }      //      private static final String TAG = "MainActivity";  } 

Step 8. declare provider in AndroidManifest

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"     package="com.example.pagingproject">      <application         android:allowBackup="true"         android:icon="@mipmap/ic_launcher"         android:label="@string/app_name"         android:supportsRtl="true"         android:theme="@style/AppTheme">         <activity android:name=".MainActivity">             <intent-filter>                 <action android:name="android.intent.action.MAIN" />                  <category android:name="android.intent.category.LAUNCHER" />             </intent-filter>         </activity>          <provider             android:name=".databases.RequestProvider"             android:authorities="${applicationId}.db"             android:exported="false" />     </application>  </manifest> 

Step 9. create xml for MainActivity class

<?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:tools="http://schemas.android.com/tools"     android:id="@+id/activity_main"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:paddingBottom="@dimen/activity_vertical_margin"     android:paddingLeft="@dimen/activity_horizontal_margin"     android:paddingRight="@dimen/activity_horizontal_margin"     android:paddingTop="@dimen/activity_vertical_margin"     tools:context="com.example.pagingproject.MainActivity">      <android.support.v7.widget.RecyclerView         android:id="@+id/recyclerView"         android:layout_width="match_parent"         android:layout_height="match_parent" /> </RelativeLayout> 

Test it:

Trigger to load more is every 30th item element, so if index starts from 0, 29 will be the trigger.