What causes "Cannot have more than one RevealableListItem with the same absolute gravity." in material-components/material-components-android?

Give each RevealableListItem a layout_gravity that matches its intended side: one start, one end — never both the same.

material-components/material-components-android · error · IllegalStateException

Cannot have more than one RevealableListItem with the same a

Error message

Cannot have more than one RevealableListItem with the same absolute gravity.

What it means

After layout, maybeSwapRevealLayoutsForGravity() re-classifies the two registered reveal children by absolute gravity (swapping their left/right slots when their declared gravity disagrees with actual alignment). If the left-aligned reveal view is actually misaligned to the right but an end-gravity reveal view is already registered, moving it would create two end-gravity views — an impossible state — so it throws IllegalStateException (first branch, leftIsMisaligned).

Source

Thrown at lib/java/com/google/android/material/listitem/ListItemLayout.java:975

        || swipeToRevealLayoutRight instanceof RevealableListItem;
  }

  private void maybeSwapRevealLayoutsForGravity() {
    boolean leftIsMisaligned =
        swipeToRevealLayoutLeft != null && isRightAligned(swipeToRevealLayoutLeft);
    boolean rightIsMisaligned =
        swipeToRevealLayoutRight != null && !isRightAligned(swipeToRevealLayoutRight);

    if (leftIsMisaligned && rightIsMisaligned) {
      View temp = swipeToRevealLayoutLeft;
      swipeToRevealLayoutLeft = swipeToRevealLayoutRight;
      swipeToRevealLayoutRight = temp;
      // If we swap, the offset should flip to keep the same active reveal layout.
      revealViewOffset *= -1;
    } else if (leftIsMisaligned) {
      // If there is already an end gravity swipeToRevealLayout, we cannot replace it.
      if (swipeToRevealLayoutRight != null) {
        throw new IllegalStateException(
            "Cannot have more than one RevealableListItem with the same absolute gravity.");
      }
      swipeToRevealLayoutRight = swipeToRevealLayoutLeft;
      swipeToRevealLayoutLeft = null;
      revealViewOffset *= -1;
    } else if (rightIsMisaligned) {
      // If there is already an start gravity swipeToRevealLayout, we cannot replace it.
      if (swipeToRevealLayoutLeft != null) {
        throw new IllegalStateException(
            "Cannot have more than one RevealableListItem with the same absolute gravity.");
      }
      swipeToRevealLayoutLeft = swipeToRevealLayoutRight;
      swipeToRevealLayoutRight = null;
      revealViewOffset *= -1;
    }
  }

  @Override

View on GitHub (pinned to ac7e18efee)

Solutions

Give each RevealableListItem a layout_gravity that matches its intended side: one start, one end — never both the same.
Use start/end (not left/right) gravities so RTL resolution stays consistent with the library's expectation.
Avoid overriding onLayout/placement of reveal children; let ListItemLayout position them.

Example fix

<!-- before: both reveal children effectively end-aligned -->
<RevealLeft  layout_gravity="right" .../>
<RevealRight layout_gravity="end" .../>

<!-- after -->
<RevealLeft  layout_gravity="start" .../>
<RevealRight layout_gravity="end" .../>

Defensive patterns

Strategy: validation

Validate before calling

View l = listItemLayout.findViewById(R.id.reveal_start);
View r = listItemLayout.findViewById(R.id.reveal_end);
if (l != null && r != null
    && sameAbsoluteGravity((ListItemLayout.LayoutParams) l.getLayoutParams(),
                           (ListItemLayout.LayoutParams) r.getLayoutParams())) {
  throw new IllegalStateException("Both reveal children share absolute gravity");
}

Prevention

Use exactly one start and one end gravity on reveal children.
Prefer start/end attributes over left/right for RTL safety.
Test list items under RTL pseudolocales in CI.

When it happens

Trigger: A ListItemLayout with two RevealableListItem children whose layout_gravity values and actual layout alignment conflict (e.g. both effectively end-aligned after layout/RTL resolution); layout direction (RTL locale) changing between inflation and layout.

Common situations: Switching locale to RTL at runtime; hand-authored XML where start/end gravities on the two reveal children do not match their positions; custom onLayout interfering with child placement.

Related errors

AI-assisted analysis of material-components/material-components-android@ac7e18efee (2026-08-14). Data as JSON: /api/errors/1d9a0c7f2c288a9b. Report an issue: GitHub.