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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 static androidx.core.util.Preconditions.checkArgument;
     20 
     21 import android.view.MotionEvent;
     22 import android.view.View;
     23 
     24 import androidx.annotation.NonNull;
     25 import androidx.annotation.Nullable;
     26 import androidx.recyclerview.widget.GridLayoutManager;
     27 import androidx.recyclerview.widget.LinearLayoutManager;
     28 import androidx.recyclerview.widget.RecyclerView;
     29 
     30 /**
     31  * Provides a means of controlling when and where band selection can be initiated.
     32  *
     33  * <p>
     34  * Two default implementations are provided: {@link EmptyArea}, and {@link NonDraggableArea}.
     35  *
     36  * @see SelectionTracker.Builder#withBandPredicate(BandPredicate)
     37  */
     38 public abstract class BandPredicate {
     39 
     40     /**
     41      * @return true if band selection can be initiated in response to the {@link MotionEvent}.
     42      */
     43     public abstract boolean canInitiate(MotionEvent e);
     44 
     45     private static boolean hasSupportedLayoutManager(@NonNull RecyclerView recyclerView) {
     46         RecyclerView.LayoutManager lm = recyclerView.getLayoutManager();
     47         return lm instanceof GridLayoutManager
     48                 || lm instanceof LinearLayoutManager;
     49     }
     50 
     51     /**
     52      * A BandPredicate that allows initiation of band selection only in areas of RecyclerView
     53      * that map to {@link RecyclerView#NO_POSITION}. In most cases, this will be the empty areas
     54      * between views.
     55      *
     56      * <p>
     57      * Use this implementation to permit band selection only in empty areas
     58      * surrounding view items. But be advised that if there is no empy area around
     59      * view items, band selection cannot be initiated.
     60      */
     61     public static final class EmptyArea extends BandPredicate {
     62 
     63         private final RecyclerView mRecyclerView;
     64 
     65         /**
     66          * @param recyclerView the owner RecyclerView
     67          */
     68         public EmptyArea(@NonNull RecyclerView recyclerView) {
     69             checkArgument(recyclerView != null);
     70 
     71             mRecyclerView = recyclerView;
     72         }
     73 
     74         @Override
     75         public boolean canInitiate(@NonNull MotionEvent e) {
     76             if (!hasSupportedLayoutManager(mRecyclerView)
     77                     || mRecyclerView.hasPendingAdapterUpdates()) {
     78                 return false;
     79             }
     80 
     81             View itemView = mRecyclerView.findChildViewUnder(e.getX(), e.getY());
     82             int position = itemView != null
     83                     ? mRecyclerView.getChildAdapterPosition(itemView)
     84                     : RecyclerView.NO_POSITION;
     85 
     86             return position == RecyclerView.NO_POSITION;
     87         }
     88     }
     89 
     90     /**
     91      * A BandPredicate that allows initiation of band selection in any area that is not
     92      * draggable as determined by consulting
     93      * {@link ItemDetailsLookup.ItemDetails#inDragRegion(MotionEvent)}. By default empty
     94      * areas (those with a position that maps to {@link RecyclerView#NO_POSITION}
     95      * are considered non-draggable.
     96      *
     97      * <p>
     98      * Use this implementation in order to permit band selection in
     99      * otherwise empty areas of a View. This is useful especially in
    100      * list layouts where there is no empty space surrounding the list items,
    101      * and individual list items may contain extra white space (like
    102      * in a list of varying length words).
    103      *
    104      * @see ItemDetailsLookup.ItemDetails#inDragRegion(MotionEvent)
    105      */
    106     public static final class NonDraggableArea extends BandPredicate {
    107 
    108         private final RecyclerView mRecyclerView;
    109         private final ItemDetailsLookup mDetailsLookup;
    110 
    111         /**
    112          * Creates a new instance.
    113          *
    114          * @param recyclerView the owner RecyclerView
    115          * @param detailsLookup provides access to item details.
    116          */
    117         public NonDraggableArea(
    118                 @NonNull RecyclerView recyclerView, @NonNull ItemDetailsLookup detailsLookup) {
    119 
    120             checkArgument(recyclerView != null);
    121             checkArgument(detailsLookup != null);
    122 
    123             mRecyclerView = recyclerView;
    124             mDetailsLookup = detailsLookup;
    125         }
    126 
    127         @Override
    128         public boolean canInitiate(@NonNull MotionEvent e) {
    129             if (!hasSupportedLayoutManager(mRecyclerView)
    130                     || mRecyclerView.hasPendingAdapterUpdates()) {
    131                 return false;
    132             }
    133 
    134             @Nullable ItemDetailsLookup.ItemDetails details = mDetailsLookup.getItemDetails(e);
    135             return (details == null) || !details.inDragRegion(e);
    136         }
    137     }
    138 }
    139