1
2/*
3 * Copyright (C) 2016 The Android Open Source Project
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
8 *
9 *      http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18package com.example.android.supportv7.widget;
19
20import android.view.LayoutInflater;
21import android.view.View;
22import android.view.ViewGroup;
23import android.widget.TextView;
24
25import androidx.core.util.Pair;
26import androidx.recyclerview.widget.DividerItemDecoration;
27import androidx.recyclerview.widget.LinearLayoutManager;
28import androidx.recyclerview.widget.RecyclerView;
29
30import com.example.android.supportv7.Cheeses;
31import com.example.android.supportv7.R;
32
33import java.util.ArrayList;
34import java.util.List;
35
36/**
37 * A sample Stable Id RecyclerView activity.
38 *
39 * Stable Ids guarantee that items that remain onscreen due to a data set change are rebound to the
40 * same views. This sample visually identifies views (independent from their data) to demonstrate
41 * how RecyclerView does this rebinding. In addition, you can observe how RecyclerView recycles
42 * items in response to a scroll or fling.
43 *
44 * Tapping an item will send it's data to the top of the list. RecyclerView will detect that the
45 * data with that stable ID has moved position, and move the View accordingly, even though the only
46 * signal sent to the RecyclerView was notifyDataSetChanged().
47 *
48 * Compared to DiffUtil or SortedList, stable Ids are often easier to use, but are less efficient,
49 * and can only look at attached views to try and form reasonable animations for an update. Note
50 * that notifyDataSetChanged() will still always cause every visible item to be rebound, since
51 * RecyclerView isn't told what *inside the item* may have changed.
52 *
53 * It is suggested instead to use DiffUtil or SortedList to dispatch minimal updates from your
54 * data set to the RecyclerView. SortedList allows you to express operations like moving or removing
55 * an item very efficiently, without RecyclerView needing to find and compare the state of each
56 * child before and after an operation. DiffUtil can compute minimal alterations (such as inserts
57 * and moves) from lists that you pass it - useful if your data source or server doesn't provide
58 * delta updates. Both DiffUtil and SortedList allow you to avoid rebinding each item when a small
59 * change occurs.
60 */
61public class StableIdActivity extends BaseLayoutManagerActivity<LinearLayoutManager> {
62    @Override
63    protected LinearLayoutManager createLayoutManager() {
64        return new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);
65    }
66
67    @Override
68    protected RecyclerView.Adapter createAdapter() {
69        return new StableIdAdapter(Cheeses.sCheeseStrings);
70    }
71
72    @Override
73    protected void onRecyclerViewInit(RecyclerView recyclerView) {
74        recyclerView.addItemDecoration(
75                new DividerItemDecoration(this, mLayoutManager.getOrientation()));
76    }
77
78    static class StableIdAdapter extends RecyclerView.Adapter<StableIdAdapter.ViewHolder> {
79        List<Pair<Integer, String>> mData = new ArrayList<>();
80
81        public static class ViewHolder extends RecyclerView.ViewHolder {
82            static int sHolderNumber = 0;
83
84            private final TextView mHolderNumberView;
85            private final TextView mDataView;
86
87            public ViewHolder(View itemView) {
88                super(itemView);
89                mHolderNumberView = (TextView) itemView.findViewById(R.id.holder_number_text);
90                mDataView = (TextView) itemView.findViewById(R.id.data_text);
91
92                // Just for demonstration, we visually uniquely identify which ViewHolder is which,
93                // so rebinding / moving due to stable IDs can be observed:
94                mHolderNumberView.setText("View Nr: " + sHolderNumber++);
95            }
96        }
97
98        StableIdAdapter(String[] strings) {
99            // comment out this line to dispatch updates without using stable IDs -
100            // this prevents RecyclerView from knowing what changed, so animations don't run
101            setHasStableIds(true);
102
103
104            for (int i = 0; i < 20; i++) {
105                mData.add(new Pair<>(500 + i, strings[i]));
106            }
107        }
108
109        @Override
110        public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
111            LayoutInflater inflater = LayoutInflater.from(parent.getContext());
112            final ViewHolder viewHolder = new ViewHolder(
113                    inflater.inflate(R.layout.stable_id_item, parent, false));
114
115            viewHolder.itemView.setOnClickListener(new View.OnClickListener() {
116                @Override
117                public void onClick(View v) {
118                    final int pos = viewHolder.getAdapterPosition();
119                    if (pos != RecyclerView.NO_POSITION) {
120                        // swap item to top, and notify data set changed
121                        Pair<Integer, String> d = mData.remove(pos);
122                        mData.add(0, d);
123
124                        notifyDataSetChanged();
125                    }
126                }
127            });
128            return viewHolder;
129        }
130
131        @Override
132        public void onBindViewHolder(ViewHolder holder, int position) {
133            holder.mDataView.setText(mData.get(position).second);
134        }
135
136        @Override
137        public long getItemId(int position) {
138            return mData.get(position).first;
139        }
140
141        @Override
142        public int getItemCount() {
143            return mData.size();
144        }
145    }
146}
147