Updating the scroll calculation from recyclerView to avoid view inflation

> Updating the LayoutManager's scroll calculation instead of a separate
  implementation to better support recyclerView's calculations
> Caching the view sizes during layout to avoid view-inflation for
  unknown types
> Fixing scrollbar jump during scroll when widget list is expanded
> Fixing scrollbar never reaching end when onboarding card is displayed
  in work tab

Bug: 240343082
Test: Verified on device that new views are not inflated
Change-Id: Ied11ccf65b053691c5c126c4bf8de306ec24786d

src/com/android/launcher3/util/ScrollableLayoutManager.java

@@ -0,0 +1,183 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.android.launcher3.util;
+
+import android.content.Context;
+import android.util.SparseIntArray;
+import android.view.View;
+
+import androidx.annotation.NonNull;
+import androidx.recyclerview.widget.GridLayoutManager;
+import androidx.recyclerview.widget.RecyclerView;
+import androidx.recyclerview.widget.RecyclerView.Adapter;
+import androidx.recyclerview.widget.RecyclerView.State;
+import androidx.recyclerview.widget.RecyclerView.ViewHolder;
+
+/**
+ * Extension of {@link GridLayoutManager} with support for smooth scrolling
+ */
+public class ScrollableLayoutManager extends GridLayoutManager {
+
+    // keyed on item type
+    protected final SparseIntArray mCachedSizes = new SparseIntArray();
+
+    private RecyclerView mRv;
+
+    /**
+     * Precalculated total height keyed on the item position. This is always incremental.
+     * Subclass can override {@link #incrementTotalHeight} to incorporate the layout logic.
+     * For example all-apps should have same values for items in same row,
+     *     sample values: 0, 10, 10, 10, 10, 20, 20, 20, 20
+     * whereas widgets will have strictly increasing values
+     *     sample values: 0, 10, 50, 60, 110
+     */
+
+    //
+    private int[] mTotalHeightCache = new int[1];
+    private int mLastValidHeightIndex = 0;
+
+    public ScrollableLayoutManager(Context context) {
+        super(context, 1, GridLayoutManager.VERTICAL, false);
+    }
+
+    @Override
+    public void onAttachedToWindow(RecyclerView view) {
+        super.onAttachedToWindow(view);
+        mRv = view;
+    }
+
+    @Override
+    public void layoutDecorated(@NonNull View child, int left, int top, int right, int bottom) {
+        super.layoutDecorated(child, left, top, right, bottom);
+        mCachedSizes.put(
+                mRv.getChildViewHolder(child).getItemViewType(), child.getMeasuredHeight());
+    }
+
+    @Override
+    public void layoutDecoratedWithMargins(@NonNull View child, int left, int top, int right,
+            int bottom) {
+        super.layoutDecoratedWithMargins(child, left, top, right, bottom);
+        mCachedSizes.put(
+                mRv.getChildViewHolder(child).getItemViewType(), child.getMeasuredHeight());
+    }
+
+    @Override
+    public int computeVerticalScrollExtent(State state) {
+        return mRv == null ? 0 : mRv.getHeight();
+    }
+
+    @Override
+    public int computeVerticalScrollOffset(State state) {
+        Adapter adapter = mRv == null ? null : mRv.getAdapter();
+        if (adapter == null) {
+            return 0;
+        }
+        if (adapter.getItemCount() == 0 || getChildCount() == 0) {
+            return 0;
+        }
+        View child = getChildAt(0);
+        ViewHolder holder = mRv.findContainingViewHolder(child);
+        if (holder == null) {
+            return 0;
+        }
+        int itemPosition = holder.getLayoutPosition();
+        if (itemPosition < 0) {
+            return 0;
+        }
+        return getPaddingTop() + getItemsHeight(adapter, itemPosition) - getDecoratedTop(child);
+    }
+
+    @Override
+    public int computeVerticalScrollRange(State state) {
+        Adapter adapter = mRv == null ? null : mRv.getAdapter();
+        return adapter == null ? 0 : getItemsHeight(adapter, adapter.getItemCount());
+    }
+
+    /**
+     * Returns the sum of the height, in pixels, of this list adapter's items from index
+     * 0 (inclusive) until {@code untilIndex} (exclusive). If untilIndex is same as the itemCount,
+     * it returns the full height of all the items.
+     *
+     * <p>If the untilIndex is larger than the total number of items in this adapter, returns the
+     * sum of all items' height.
+     */
+    private int getItemsHeight(Adapter adapter, int untilIndex) {
+        final int totalItems = adapter.getItemCount();
+        if (mTotalHeightCache.length < (totalItems + 1)) {
+            mTotalHeightCache = new int[totalItems + 1];
+            mLastValidHeightIndex = 0;
+        }
+        if (untilIndex > totalItems) {
+            untilIndex = totalItems;
+        } else if (untilIndex < 0) {
+            untilIndex = 0;
+        }
+        if (untilIndex <= mLastValidHeightIndex) {
+            return mTotalHeightCache[untilIndex];
+        }
+
+        int totalItemsHeight = mTotalHeightCache[mLastValidHeightIndex];
+        for (int i = mLastValidHeightIndex; i < untilIndex; i++) {
+            totalItemsHeight = incrementTotalHeight(adapter, i, totalItemsHeight);
+            mTotalHeightCache[i + 1] = totalItemsHeight;
+        }
+        mLastValidHeightIndex = untilIndex;
+        return totalItemsHeight;
+    }
+
+    /**
+     * The current implementation assumes a linear list with every item taking up the whole row.
+     * Subclasses should override this method to account for any spanning logic
+     */
+    protected int incrementTotalHeight(Adapter adapter, int position, int heightUntilLastPos) {
+        return heightUntilLastPos + mCachedSizes.get(adapter.getItemViewType(position));
+    }
+
+    private void invalidateScrollCache() {
+        mLastValidHeightIndex = 0;
+    }
+
+    @Override
+    public void onItemsAdded(RecyclerView recyclerView, int positionStart, int itemCount) {
+        super.onItemsAdded(recyclerView, positionStart, itemCount);
+        invalidateScrollCache();
+    }
+
+    @Override
+    public void onItemsChanged(RecyclerView recyclerView) {
+        super.onItemsChanged(recyclerView);
+        invalidateScrollCache();
+    }
+
+    @Override
+    public void onItemsRemoved(RecyclerView recyclerView, int positionStart, int itemCount) {
+        super.onItemsRemoved(recyclerView, positionStart, itemCount);
+        invalidateScrollCache();
+    }
+
+    @Override
+    public void onItemsMoved(RecyclerView recyclerView, int from, int to, int itemCount) {
+        super.onItemsMoved(recyclerView, from, to, itemCount);
+        invalidateScrollCache();
+    }
+
+    @Override
+    public void onItemsUpdated(RecyclerView recyclerView, int positionStart, int itemCount,
+            Object payload) {
+        super.onItemsUpdated(recyclerView, positionStart, itemCount, payload);
+        invalidateScrollCache();
+    }
+}