[Carousel] Prevent scrolling if there's less items than focal keylines

PiperOrigin-RevId: 625466841

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

@@ -784,6 +784,10 @@ private static KeylineRange getSurroundingKeylineRange(
  keylines.get(startMinDistanceIndex), keylines.get(endMinDistanceIndex));
  }
 
+ private KeylineState getKeylineStartingState(KeylineStateList keylineStateList) {
+ return isLayoutRtl() ? keylineStateList.getEndState() : keylineStateList.getStartState();
+ }
+
  /**
  * Update the current keyline state by shifting it in response to any change in scroll offset.
  *
@@ -794,8 +798,7 @@ private void updateCurrentKeylineStateForScrollOffset(
  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.
- this.currentKeylineState =
- isLayoutRtl() ? keylineStateList.getEndState() : keylineStateList.getStartState();
+ this.currentKeylineState = getKeylineStartingState(keylineStateList);
  } else {
  this.currentKeylineState =
  keylineStateList.getShiftedState(scrollOffset, minScroll, maxScroll);
@@ -1454,6 +1457,12 @@ private int scrollBy(int distance, Recycler recycler, State state) {
  recalculateKeylineStateList(recycler);
  }
 
+ // If the number of items is equal or less than the number of focal items, we should not be able
+ // to scroll.
+ if (getItemCount() <= getKeylineStartingState(keylineStateList).getTotalVisibleFocalItems()) {
+ return 0;
+ }
+
  // Calculate how much the carousel should scroll and update the scroll offset.
  int scrolledBy = calculateShouldScrollBy(distance, scrollOffset, minScroll, maxScroll);
  scrollOffset += scrolledBy;

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

@@ -52,6 +52,7 @@
 final class KeylineState {
 
  private final float itemSize;
+ private int totalVisibleFocalItems;
  private final List<Keyline> keylines;
  private final int firstFocalKeylineIndex;
  private final int lastFocalKeylineIndex;
@@ -65,6 +66,11 @@ private KeylineState(
  this.keylines = Collections.unmodifiableList(keylines);
  this.firstFocalKeylineIndex = firstFocalKeylineIndex;
  this.lastFocalKeylineIndex = lastFocalKeylineIndex;
+ for (int i = firstFocalKeylineIndex; i <= lastFocalKeylineIndex; i++) {
+ if (keylines.get(i).cutoff == 0) {
+ this.totalVisibleFocalItems += 1;
+ }
+ }
  }
 
  /**
@@ -81,6 +87,11 @@ List<Keyline> getKeylines() {
  return keylines;
  }
 
+ /** Returns the number of focal items in the keyline state. */
+ int getTotalVisibleFocalItems() {
+ return totalVisibleFocalItems;
+ }
+
  /** Returns the first focal keyline in the list. */
  Keyline getFirstFocalKeyline() {
  return keylines.get(firstFocalKeylineIndex);

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

@@ -614,6 +614,18 @@ public void testRequestChildRectangleOnScreen_doesntScrollIfChildIsFocal() throw
  assertThat(layoutManager.scrollOffset).isEqualTo(0);
  }
 
+ @Test
+ public void testSingleItem_shouldNotScrollWithPadding() throws Throwable {
+ recyclerView.setPadding(50, 0, 50, 0);
+ recyclerView.setClipToPadding(false);
+ setAdapterItems(recyclerView, layoutManager, adapter, createDataSetWithSize(1));
+ int originalLeft = recyclerView.getChildAt(0).getLeft();
+
+ scrollHorizontallyBy(recyclerView, layoutManager, 100);
+
+ assertThat(recyclerView.getChildAt(0).getLeft()).isEqualTo(originalLeft);
+ }
+
  /**
  * Assigns explicit sizes to fixtures being used to construct the testing environment.
  *