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https://github.com/M66B/FairEmail.git
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Compile paging inline
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M66B
231
app/src/main/java/androidx/paging/PagedStorageDiffHelper.java
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231
app/src/main/java/androidx/paging/PagedStorageDiffHelper.java
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/*
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* Copyright (C) 2017 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package androidx.paging;
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import androidx.annotation.NonNull;
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import androidx.annotation.Nullable;
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import androidx.recyclerview.widget.DiffUtil;
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import androidx.recyclerview.widget.ListUpdateCallback;
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/**
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* Methods for computing and applying DiffResults between PagedLists.
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*
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* To minimize the amount of diffing caused by placeholders, we only execute DiffUtil in a reduced
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* 'diff space' - in the range (computeLeadingNulls..size-computeTrailingNulls).
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*
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* This allows the diff of a PagedList, e.g.:
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* 100 nulls, placeholder page, (empty page) x 5, page, 100 nulls
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*
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* To only inform DiffUtil about single loaded page in this case, by pruning all other nulls from
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* consideration.
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*
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* @see PagedStorage#computeLeadingNulls()
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* @see PagedStorage#computeTrailingNulls()
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*/
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class PagedStorageDiffHelper {
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private PagedStorageDiffHelper() {
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}
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static <T> DiffUtil.DiffResult computeDiff(
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final PagedStorage<T> oldList,
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final PagedStorage<T> newList,
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final DiffUtil.ItemCallback<T> diffCallback) {
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final int oldOffset = oldList.computeLeadingNulls();
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final int newOffset = newList.computeLeadingNulls();
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final int oldSize = oldList.size() - oldOffset - oldList.computeTrailingNulls();
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final int newSize = newList.size() - newOffset - newList.computeTrailingNulls();
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return DiffUtil.calculateDiff(new DiffUtil.Callback() {
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@Nullable
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@Override
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public Object getChangePayload(int oldItemPosition, int newItemPosition) {
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T oldItem = oldList.get(oldItemPosition + oldOffset);
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T newItem = newList.get(newItemPosition + newList.getLeadingNullCount());
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if (oldItem == null || newItem == null) {
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return null;
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}
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return diffCallback.getChangePayload(oldItem, newItem);
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}
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@Override
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public int getOldListSize() {
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return oldSize;
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}
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@Override
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public int getNewListSize() {
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return newSize;
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}
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@Override
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public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
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T oldItem = oldList.get(oldItemPosition + oldOffset);
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T newItem = newList.get(newItemPosition + newList.getLeadingNullCount());
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if (oldItem == newItem) {
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return true;
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}
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//noinspection SimplifiableIfStatement
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if (oldItem == null || newItem == null) {
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return false;
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}
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return diffCallback.areItemsTheSame(oldItem, newItem);
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}
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@Override
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public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
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T oldItem = oldList.get(oldItemPosition + oldOffset);
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T newItem = newList.get(newItemPosition + newList.getLeadingNullCount());
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if (oldItem == newItem) {
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return true;
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}
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//noinspection SimplifiableIfStatement
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if (oldItem == null || newItem == null) {
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return false;
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}
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return diffCallback.areContentsTheSame(oldItem, newItem);
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}
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}, true);
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}
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private static class OffsettingListUpdateCallback implements ListUpdateCallback {
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private final int mOffset;
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private final ListUpdateCallback mCallback;
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OffsettingListUpdateCallback(int offset, ListUpdateCallback callback) {
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mOffset = offset;
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mCallback = callback;
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}
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@Override
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public void onInserted(int position, int count) {
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mCallback.onInserted(position + mOffset, count);
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}
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@Override
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public void onRemoved(int position, int count) {
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mCallback.onRemoved(position + mOffset, count);
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}
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@Override
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public void onMoved(int fromPosition, int toPosition) {
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mCallback.onMoved(fromPosition + mOffset, toPosition + mOffset);
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}
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@Override
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public void onChanged(int position, int count, Object payload) {
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mCallback.onChanged(position + mOffset, count, payload);
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}
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}
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/**
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* TODO: improve diffing logic
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*
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* This function currently does a naive diff, assuming null does not become an item, and vice
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* versa (so it won't dispatch onChange events for these). It's similar to passing a list with
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* leading/trailing nulls in the beginning / end to DiffUtil, but dispatches the remove/insert
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* for changed nulls at the beginning / end of the list.
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*
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* Note: if lists mutate between diffing the snapshot and dispatching the diff here, then we
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* handle this by passing the snapshot to the callback, and dispatching those changes
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* immediately after dispatching this diff.
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*/
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static <T> void dispatchDiff(ListUpdateCallback callback,
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final PagedStorage<T> oldList,
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final PagedStorage<T> newList,
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final DiffUtil.DiffResult diffResult) {
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final int trailingOld = oldList.computeTrailingNulls();
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final int trailingNew = newList.computeTrailingNulls();
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final int leadingOld = oldList.computeLeadingNulls();
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final int leadingNew = newList.computeLeadingNulls();
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if (trailingOld == 0
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&& trailingNew == 0
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&& leadingOld == 0
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&& leadingNew == 0) {
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// Simple case, dispatch & return
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diffResult.dispatchUpdatesTo(callback);
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return;
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}
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// First, remove or insert trailing nulls
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if (trailingOld > trailingNew) {
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int count = trailingOld - trailingNew;
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callback.onRemoved(oldList.size() - count, count);
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} else if (trailingOld < trailingNew) {
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callback.onInserted(oldList.size(), trailingNew - trailingOld);
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}
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// Second, remove or insert leading nulls
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if (leadingOld > leadingNew) {
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callback.onRemoved(0, leadingOld - leadingNew);
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} else if (leadingOld < leadingNew) {
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callback.onInserted(0, leadingNew - leadingOld);
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}
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// apply the diff, with an offset if needed
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if (leadingNew != 0) {
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diffResult.dispatchUpdatesTo(new OffsettingListUpdateCallback(leadingNew, callback));
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} else {
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diffResult.dispatchUpdatesTo(callback);
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}
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}
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/**
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* Given an oldPosition representing an anchor in the old data set, computes its new position
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* after the diff, or a guess if it no longer exists.
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*/
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static int transformAnchorIndex(@NonNull DiffUtil.DiffResult diffResult,
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@NonNull PagedStorage oldList, @NonNull PagedStorage newList, final int oldPosition) {
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final int oldOffset = oldList.computeLeadingNulls();
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// diffResult's indices starting after nulls, need to transform to diffutil indices
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// (see also dispatchDiff(), which adds this offset when dispatching)
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int diffIndex = oldPosition - oldOffset;
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final int oldSize = oldList.size() - oldOffset - oldList.computeTrailingNulls();
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// if our anchor is non-null, use it or close item's position in new list
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if (diffIndex >= 0 && diffIndex < oldSize) {
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// search outward from old position for position that maps
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for (int i = 0; i < 30; i++) {
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int positionToTry = diffIndex + (i / 2 * (i % 2 == 1 ? -1 : 1));
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// reject if (null) item was not passed to DiffUtil, and wouldn't be in the result
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if (positionToTry < 0 || positionToTry >= oldList.getStorageCount()) {
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continue;
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}
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try {
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int result = diffResult.convertOldPositionToNew(positionToTry);
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if (result != -1) {
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// also need to transform from diffutil output indices to newList
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return result + newList.getLeadingNullCount();
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}
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} catch (IndexOutOfBoundsException e) {
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// Rare crash, just give up the search for the old item
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break;
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}
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}
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}
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// not anchored to an item in new list, so just reuse position (clamped to newList size)
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return Math.max(0, Math.min(oldPosition, newList.size() - 1));
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}
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}
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