[Carousel] Add a layout listener to recyclerview to refresh keyline state upon size change

PiperOrigin-RevId: 551280769

Author: imhappi

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

@@ -40,6 +40,7 @@
 import android.util.AttributeSet;
 import android.util.Log;
 import android.view.View;
+import android.view.View.OnLayoutChangeListener;
 import android.view.ViewGroup;
 import android.view.accessibility.AccessibilityEvent;
 import androidx.annotation.IntDef;
@@ -115,14 +116,18 @@ public class CarouselLayoutManager extends LayoutManager
 
   private CarouselOrientationHelper orientationHelper;
 
-  /**
-   * Aligns large items to the start of the carousel.
-   */
+  private final OnLayoutChangeListener recyclerViewSizeChangeListener =
+      (v, left, top, right, bottom, oldLeft, oldTop, oldRight, oldBottom) -> {
+        // If RV dimen values have changed, refresh the keyline state.
+        if (left != oldLeft || top != oldTop || right != oldRight || bottom != oldBottom) {
+          v.post(this::refreshKeylineState);
+        }
+      };
+
+  /** Aligns large items to the start of the carousel. */
   public static final int ALIGNMENT_START = 0;
 
-  /**
-   * Aligns large items to the center of the carousel.
-   */
+  /** Aligns large items to the center of the carousel. */
   public static final int ALIGNMENT_CENTER = 1;
 
   /**
@@ -226,9 +231,14 @@ public void setCarouselStrategy(@NonNull CarouselStrategy carouselStrategy) {
   @Override
   public void onAttachedToWindow(RecyclerView view) {
     super.onAttachedToWindow(view);
-    // TODO: b/291123558 - Keylines should be also be refreshed when
-    // there's any change affecting dimens of the RecyclerView.
     refreshKeylineState();
+    view.addOnLayoutChangeListener(recyclerViewSizeChangeListener);
+  }
+
+  @Override
+  public void onDetachedFromWindow(RecyclerView view, Recycler recycler) {
+    super.onDetachedFromWindow(view, recycler);
+    view.removeOnLayoutChangeListener(recyclerViewSizeChangeListener);
   }
 
   @Override
@@ -241,16 +251,11 @@ public void onLayoutChildren(Recycler recycler, State state) {
 
     boolean isRtl = isLayoutRtl();
 
+    boolean isInitialLoad = keylineStateList == null;
     // If a keyline state hasn't been created, use the first child as a representative of how each
     // child would like to be measured and allow the strategy to create a keyline state.
-    boolean isInitialLoad = keylineStateList == null;
     if (isInitialLoad) {
-      View firstChild = recycler.getViewForPosition(0);
-      measureChildWithMargins(firstChild, 0, 0);
-      KeylineState keylineState =
-          carouselStrategy.onFirstChildMeasuredWithMargins(this, firstChild);
-      keylineStateList =
-          KeylineStateList.from(this, isRtl ? KeylineState.reverse(keylineState) : keylineState);
+      recalculateKeylineStateList(recycler);
     }
 
     // Ensure our scroll limits are initialized and valid for the data set size.
@@ -277,12 +282,21 @@ public void onLayoutChildren(Recycler recycler, State state) {
     // Ensure currentFillStartPosition is valid if the number of items in the adapter has changed.
     currentFillStartPosition = MathUtils.clamp(currentFillStartPosition, 0, state.getItemCount());
 
-    updateCurrentKeylineStateForScrollOffset();
+    updateCurrentKeylineStateForScrollOffset(keylineStateList);
 
     detachAndScrapAttachedViews(recycler);
     fill(recycler, state);
   }
 
+  private void recalculateKeylineStateList(Recycler recycler) {
+    View firstChild = recycler.getViewForPosition(0);
+    measureChildWithMargins(firstChild, 0, 0);
+    KeylineState keylineState = carouselStrategy.onFirstChildMeasuredWithMargins(this, firstChild);
+    keylineStateList =
+        KeylineStateList.from(
+            this, isLayoutRtl() ? KeylineState.reverse(keylineState) : keylineState);
+  }
+
   /**
    * Recalculates the {@link KeylineState} and {@link KeylineStateList} for the current strategy.
    */
@@ -683,7 +697,8 @@ private static KeylineRange getSurroundingKeylineRange(
    *
    * <p>This method should be called any time a change in the scroll offset occurs.
    */
-  private void updateCurrentKeylineStateForScrollOffset() {
+  private void updateCurrentKeylineStateForScrollOffset(
+      @NonNull KeylineStateList keylineStateList) {
     if (maxScroll <= minScroll) {
       // We don't have enough items in the list to scroll and we should use the keyline state
       // that aligns items to the start of the container.
@@ -697,9 +712,9 @@ private void updateCurrentKeylineStateForScrollOffset() {
   }
 
   /**
-   * Calculates the horizontal distance children should be scrolled by for a given {@code dx}.
+   * Calculates the distance children should be scrolled by for a given {@code delta}.
    *
-   * @param dx the delta, resulting from a gesture or other event, that the list would like to be
+   * @param delta the delta, resulting from a gesture or other event, that the list would like to be
    *     scrolled by
    * @param currentScroll the current horizontal scroll offset that is always between the min and
    *     max horizontal scroll
@@ -724,7 +739,7 @@ private static int calculateShouldScrollBy(
    * Calculates the total offset needed to scroll the first item in the list to the center of the
    * start focal keyline.
    */
-  private int calculateStartScroll(KeylineStateList stateList) {
+  private int calculateStartScroll(@NonNull KeylineStateList stateList) {
     boolean isRtl = isLayoutRtl();
     KeylineState startState = isRtl ? stateList.getEndState() : stateList.getStartState();
     Keyline startFocalKeyline =
@@ -1106,7 +1121,7 @@ public void scrollToPosition(int position) {
     }
     scrollOffset = getScrollOffsetForPosition(position, getKeylineStateForPosition(position));
     currentFillStartPosition = MathUtils.clamp(position, 0, max(0, getItemCount() - 1));
-    updateCurrentKeylineStateForScrollOffset();
+    updateCurrentKeylineStateForScrollOffset(keylineStateList);
     requestLayout();
   }
 
@@ -1211,10 +1226,14 @@ private int scrollBy(int distance, Recycler recycler, State state) {
       return 0;
     }
 
+    if (keylineStateList == null) {
+      recalculateKeylineStateList(recycler);
+    }
+
     // Calculate how much the carousel should scroll and update the scroll offset.
     int scrolledBy = calculateShouldScrollBy(distance, scrollOffset, minScroll, maxScroll);
     scrollOffset += scrolledBy;
-    updateCurrentKeylineStateForScrollOffset();
+    updateCurrentKeylineStateForScrollOffset(keylineStateList);
 
     float halfItemSize = currentKeylineState.getItemSize() / 2F;
     int startPosition = getPosition(getChildAt(0));
@@ -1278,7 +1297,7 @@ public int computeHorizontalScrollOffset(@NonNull State state) {
    */
   @Override
   public int computeHorizontalScrollExtent(@NonNull State state) {
-    return (int) keylineStateList.getDefaultState().getItemSize();
+    return keylineStateList == null ? 0 : (int) keylineStateList.getDefaultState().getItemSize();
   }
 
   /**
@@ -1300,7 +1319,7 @@ public int computeVerticalScrollOffset(@NonNull State state) {
 
   @Override
   public int computeVerticalScrollExtent(@NonNull State state) {
-    return (int) keylineStateList.getDefaultState().getItemSize();
+    return keylineStateList == null ? 0 : (int) keylineStateList.getDefaultState().getItemSize();
   }
 
   @Override

lib/javatests/com/google/android/material/carousel/CarouselLayoutManagerRtlTest.java

@@ -43,6 +43,7 @@
 import org.junit.runner.RunWith;
 import org.robolectric.Robolectric;
 import org.robolectric.RobolectricTestRunner;
+import org.robolectric.annotation.Config;
 
 /** RTL tests for {@link CarouselLayoutManager}. */
 @RunWith(RobolectricTestRunner.class)
@@ -87,17 +88,10 @@ public void testFirstAdapterItem_isDrawnAtRightOfContainer() throws Throwable {
     assertThat(firstChild.getRight()).isEqualTo(DEFAULT_RECYCLER_VIEW_WIDTH);
   }
 
+  @Config(qualifiers = "sw1320dp-w1320dp")
   @Test
   public void testScrollBeyondMaxHorizontalScroll_shouldLimitToMaxScrollOffset() throws Throwable {
     KeylineState keylineState = getTestCenteredKeylineState();
-    layoutManager.setCarouselStrategy(
-        new CarouselStrategy() {
-          @Override
-          KeylineState onFirstChildMeasuredWithMargins(
-              @NonNull Carousel carousel, @NonNull View child) {
-            return keylineState;
-          }
-        });
     setAdapterItems(recyclerView, layoutManager, adapter, createDataSetWithSize(10));
     scrollToPosition(recyclerView, layoutManager, 200);