[Carousel] Add a11y focus scrolling support

PiperOrigin-RevId: 505783943

lib/java/com/google/android/material/carousel/CarouselAccessibilityDelegate.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2023 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
+ *
+ *     https://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.google.android.material.carousel;
+
+import android.graphics.Rect;
+import androidx.recyclerview.widget.RecyclerView;
+import androidx.recyclerview.widget.RecyclerViewAccessibilityDelegate;
+import android.view.View;
+import android.view.ViewGroup;
+import android.view.accessibility.AccessibilityEvent;
+import androidx.annotation.NonNull;
+
+/** A class that handles accessibility for CarouselLayoutManager. */
+final class CarouselAccessibilityDelegate extends RecyclerViewAccessibilityDelegate {
+
+  public CarouselAccessibilityDelegate(@NonNull RecyclerView recyclerView) {
+    super(recyclerView);
+  }
+
+  @Override
+  public boolean onRequestSendAccessibilityEvent(
+      @NonNull ViewGroup host, @NonNull View child, @NonNull AccessibilityEvent event) {
+    switch (event.getEventType()) {
+        // Allow every child in the carousel an opportunity to bring itself into the focal range
+        // when focused by accessibility.
+      case AccessibilityEvent.TYPE_VIEW_ACCESSIBILITY_FOCUSED:
+        RecyclerView rv = (RecyclerView) host;
+        Rect rect = new Rect(0, 0, child.getWidth(), child.getHeight());
+        rv.getLayoutManager()
+            .requestChildRectangleOnScreen(
+                (RecyclerView) host,
+                child,
+                rect,
+                /* immediate= */ true,
+                /* focusedChildVisible= */ false);
+        return true;
+      default:
+        return super.onRequestSendAccessibilityEvent(host, child, event);
+    }
+  }
+}

lib/java/com/google/android/material/carousel/CarouselLayoutManager.java

@@ -35,6 +35,7 @@
 import android.util.AttributeSet;
 import android.view.View;
 import android.view.ViewGroup;
+import android.view.accessibility.AccessibilityEvent;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.RestrictTo;
@@ -120,6 +121,18 @@ public CarouselLayoutManager(
     // TODO(b/238620200): Add and obtain carousel attrs set on RecyclerView
   }
 
+  @Override
+  public void onAttachedToWindow(RecyclerView view) {
+    super.onAttachedToWindow(view);
+    view.setAccessibilityDelegateCompat(new CarouselAccessibilityDelegate(view));
+  }
+
+  @Override
+  public void onDetachedFromWindow(RecyclerView view, Recycler recycler) {
+    super.onDetachedFromWindow(view, recycler);
+    view.setAccessibilityDelegateCompat(null);
+  }
+
   @Override
   public LayoutParams generateDefaultLayoutParams() {
     return new LayoutParams(
@@ -724,6 +737,15 @@ private int addEnd(int value, int amount) {
     return isLayoutRtl() ? value - amount : value + amount;
   }
 
+  @Override
+  public void onInitializeAccessibilityEvent(@NonNull AccessibilityEvent event) {
+    super.onInitializeAccessibilityEvent(event);
+    if (getChildCount() > 0) {
+      event.setFromIndex(getPosition(getChildAt(0)));
+      event.setToIndex(getPosition(getChildAt(getChildCount() - 1)));
+    }
+  }
+
   /**
    * Gets the scroll offset for a position in the adapter.
    *
@@ -768,6 +790,30 @@ public int scrollHorizontallyBy(int dx, Recycler recycler, State state) {
     return canScrollHorizontally() ? scrollBy(dx, recycler, state) : 0;
   }
 
+  @Override
+  public boolean requestChildRectangleOnScreen(
+      @NonNull RecyclerView parent,
+      @NonNull View child,
+      @NonNull Rect rect,
+      boolean immediate,
+      boolean focusedChildVisible) {
+    if (keylineStateList == null) {
+      return false;
+    }
+
+    int offsetForChild =
+        getScrollOffsetForPosition(keylineStateList.getDefaultState(), getPosition(child));
+    int dx = offsetForChild - horizontalScrollOffset;
+    if (!focusedChildVisible) {
+      if (dx != 0) {
+        // TODO(b/266816148): Implement smoothScrollBy when immediate is false.
+        parent.scrollBy(dx, 0);
+        return true;
+      }
+    }
+    return false;
+  }
+
   /**
    * Offset child items, respecting min and max scroll offsets, and fill additional space with new
    * items.
@@ -832,6 +878,45 @@ private void offsetChildLeftAndRight(
     child.offsetLeftAndRight((int) (offsetCx - actualCx));
   }
 
+  /**
+   * Calculate the offset of the horizontal scrollbar thumb within the horizontal range. This is the
+   * position of the thumb within the scrollbar track.
+   *
+   * <p>This is also used for accessibility when scrolling to give auditory feedback about the
+   * current scroll position within the total range.
+   *
+   * <p>This method can return an arbitrary unit as long as the unit is shared across {@link
+   * #computeHorizontalScrollExtent(State)} and {@link #computeHorizontalScrollRange(State)}.
+   */
+  @Override
+  public int computeHorizontalScrollOffset(@NonNull State state) {
+    return horizontalScrollOffset;
+  }
+
+  /**
+   * Compute the extent of the horizontal scrollbar thumb. This is the size of the thumb inside the
+   * scrollbar track.
+   *
+   * <p>This method can return an arbitrary unit as long as the unit is shared across {@link
+   * #computeHorizontalScrollExtent(State)} and {@link #computeHorizontalScrollOffset(State)}.
+   */
+  @Override
+  public int computeHorizontalScrollExtent(@NonNull State state) {
+    return (int) keylineStateList.getDefaultState().getItemSize();
+  }
+
+  /**
+   * Compute the horizontal range represented by the horizontal scroll bars. This is the total
+   * length of the scrollbar track within the range.
+   *
+   * <p>This method can return an arbitrary unit as long as the unit is shared across {@link
+   * #computeHorizontalScrollExtent(State)} and {@link #computeHorizontalScrollOffset(State)}.
+   */
+  @Override
+  public int computeHorizontalScrollRange(@NonNull State state) {
+    return maxHorizontalScroll - minHorizontalScroll;
+  }
+
   /**
    * Enables drawing that illustrates keylines and other internal concepts to help debug
    * configurations.