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      1 /*
      2  * Copyright (C) 2017 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 package androidx.room.integration.testapp.database;
     17 
     18 import androidx.annotation.NonNull;
     19 import androidx.paging.DataSource;
     20 import androidx.paging.ItemKeyedDataSource;
     21 import androidx.room.InvalidationTracker;
     22 
     23 import java.util.Collections;
     24 import java.util.List;
     25 import java.util.Set;
     26 
     27 /**
     28  * Sample Room keyed data source.
     29  */
     30 public class LastNameAscCustomerDataSource extends ItemKeyedDataSource<String, Customer> {
     31     private final CustomerDao mCustomerDao;
     32     @SuppressWarnings("FieldCanBeLocal")
     33     private final InvalidationTracker.Observer mObserver;
     34     private SampleDatabase mDb;
     35 
     36     public static Factory<String, Customer> factory(final SampleDatabase db) {
     37         return new Factory<String, Customer>() {
     38             @Override
     39             public DataSource<String, Customer> create() {
     40                 return new LastNameAscCustomerDataSource(db);
     41             }
     42         };
     43     }
     44 
     45     /**
     46      * Create a DataSource from the customer table of the given database
     47      */
     48     private LastNameAscCustomerDataSource(SampleDatabase db) {
     49         mDb = db;
     50         mCustomerDao = db.getCustomerDao();
     51         mObserver = new InvalidationTracker.Observer("customer") {
     52             @Override
     53             public void onInvalidated(@NonNull Set<String> tables) {
     54                 invalidate();
     55             }
     56         };
     57         db.getInvalidationTracker().addWeakObserver(mObserver);
     58     }
     59 
     60     @Override
     61     public boolean isInvalid() {
     62         mDb.getInvalidationTracker().refreshVersionsSync();
     63         return super.isInvalid();
     64     }
     65 
     66     @NonNull
     67     public static String getKeyStatic(@NonNull Customer customer) {
     68         return customer.getLastName();
     69     }
     70 
     71     @NonNull
     72     @Override
     73     public String getKey(@NonNull Customer customer) {
     74         return getKeyStatic(customer);
     75     }
     76 
     77     @Override
     78     public void loadInitial(@NonNull LoadInitialParams<String> params,
     79             @NonNull LoadInitialCallback<Customer> callback) {
     80         String customerName = params.requestedInitialKey;
     81         List<Customer> list;
     82         if (customerName != null) {
     83             // initial keyed load - load before 'customerName',
     84             // and load after last item in before list
     85             int pageSize = params.requestedLoadSize / 2;
     86             String key = customerName;
     87             list = mCustomerDao.customerNameLoadBefore(key, pageSize);
     88             Collections.reverse(list);
     89             if (!list.isEmpty()) {
     90                 key = getKey(list.get(list.size() - 1));
     91             }
     92             list.addAll(mCustomerDao.customerNameLoadAfter(key, pageSize));
     93         } else {
     94             list = mCustomerDao.customerNameInitial(params.requestedLoadSize);
     95         }
     96 
     97         if (params.placeholdersEnabled && !list.isEmpty()) {
     98             String firstKey = getKey(list.get(0));
     99             String lastKey = getKey(list.get(list.size() - 1));
    100 
    101             // only bother counting if placeholders are desired
    102             final int position = mCustomerDao.customerNameCountBefore(firstKey);
    103             final int count = position + list.size() + mCustomerDao.customerNameCountAfter(lastKey);
    104             callback.onResult(list, position, count);
    105         } else {
    106             callback.onResult(list);
    107         }
    108     }
    109 
    110     @Override
    111     public void loadAfter(@NonNull LoadParams<String> params,
    112             @NonNull LoadCallback<Customer> callback) {
    113         callback.onResult(mCustomerDao.customerNameLoadAfter(params.key, params.requestedLoadSize));
    114     }
    115 
    116     @Override
    117     public void loadBefore(@NonNull LoadParams<String> params,
    118             @NonNull LoadCallback<Customer> callback) {
    119         List<Customer> list = mCustomerDao.customerNameLoadBefore(
    120                 params.key, params.requestedLoadSize);
    121         Collections.reverse(list);
    122         callback.onResult(list);
    123     }
    124 }
    125 
    126