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      1 /*
      2  * Copyright 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 
     17 package androidx.recyclerview.selection;
     18 
     19 import android.util.SparseArray;
     20 import android.view.View;
     21 
     22 import androidx.annotation.NonNull;
     23 import androidx.annotation.Nullable;
     24 import androidx.recyclerview.widget.RecyclerView;
     25 import androidx.recyclerview.widget.RecyclerView.OnChildAttachStateChangeListener;
     26 
     27 import java.util.HashMap;
     28 import java.util.Map;
     29 
     30 /**
     31  * An {@link ItemKeyProvider} that provides stable ids by way of cached
     32  * {@link RecyclerView.Adapter} stable ids. Items enter the cache as they are laid out by
     33  * RecyclerView, and are removed from the cache as they are recycled.
     34  *
     35  * <p>
     36  * There are trade-offs with this implementation as it necessarily auto-boxes {@code long}
     37  * stable id values into {@code Long} values for use as selection keys. The core Selection API
     38  * uses a parameterized key type to permit other keys (such as Strings or URIs).
     39  */
     40 public final class StableIdKeyProvider extends ItemKeyProvider<Long> {
     41 
     42     private final SparseArray<Long> mPositionToKey = new SparseArray<>();
     43     private final Map<Long, Integer> mKeyToPosition = new HashMap<Long, Integer>();
     44     private final RecyclerView mRecyclerView;
     45 
     46     /**
     47      * Creates a new key provider that uses cached {@code long} stable ids associated
     48      * with the RecyclerView items.
     49      *
     50      * @param recyclerView the owner RecyclerView
     51      */
     52     public StableIdKeyProvider(@NonNull RecyclerView recyclerView) {
     53 
     54         // Since this provide is based on stable ids based on whats laid out in the window
     55         // we can only satisfy "window" scope key access.
     56         super(SCOPE_CACHED);
     57 
     58         mRecyclerView = recyclerView;
     59 
     60         mRecyclerView.addOnChildAttachStateChangeListener(
     61                 new OnChildAttachStateChangeListener() {
     62                     @Override
     63                     public void onChildViewAttachedToWindow(View view) {
     64                         onAttached(view);
     65                     }
     66 
     67                     @Override
     68                     public void onChildViewDetachedFromWindow(View view) {
     69                         onDetached(view);
     70                     }
     71                 }
     72         );
     73 
     74     }
     75 
     76     private void onAttached(@NonNull View view) {
     77         RecyclerView.ViewHolder holder = mRecyclerView.findContainingViewHolder(view);
     78         int position = holder.getAdapterPosition();
     79         long id = holder.getItemId();
     80         if (position != RecyclerView.NO_POSITION && id != RecyclerView.NO_ID) {
     81             mPositionToKey.put(position, id);
     82             mKeyToPosition.put(id, position);
     83         }
     84     }
     85 
     86     private void onDetached(@NonNull View view) {
     87         RecyclerView.ViewHolder holder = mRecyclerView.findContainingViewHolder(view);
     88         int position = holder.getAdapterPosition();
     89         long id = holder.getItemId();
     90         if (position != RecyclerView.NO_POSITION && id != RecyclerView.NO_ID) {
     91             mPositionToKey.delete(position);
     92             mKeyToPosition.remove(id);
     93         }
     94     }
     95 
     96     @Override
     97     public @Nullable Long getKey(int position) {
     98         return mPositionToKey.get(position, null);
     99     }
    100 
    101     @Override
    102     public int getPosition(@NonNull Long key) {
    103         if (mKeyToPosition.containsKey(key)) {
    104             return mKeyToPosition.get(key);
    105         }
    106         return RecyclerView.NO_POSITION;
    107     }
    108 }
    109