Reanimated Layout Animations: Auto-Morphing Views

WHY IT EXISTS: React Native layout changes normally snap instantly. Measuring views and manually driving width, height, or position through JavaScript shared values is fragile because you must await layout events, handle race conditions, and keep measurements in sync with flex changes. Reanimated layout animations exist to remove that burden by letting the native side detect geometry changes and interpolate between them automatically.

THE MENTAL MODEL: Treat layout animations as an automatic diff for view geometry. Instead of thinking about animating width or top, picture two snapshots of a view's bounding box: the frame before React Native recalculates layout and the frame after. Reanimated bridges the gap by morphing the view from the old origin and size to the new ones on the UI thread. You are not declaring target values; you are telling the engine to animate whatever the next layout pass produces.

HOW IT WORKS: You assign a layout prop such as Layout.springify() to an Animated.View. When the component mounts, unmounts, or its shadow node layout changes due to style updates, sibling additions, or conditional rendering, Reanimated's native plugin intercepts the before and after metrics. It records the previous bounds and the new bounds, then runs an animation entirely in native code to transition between those states. Because the work stays off the JavaScript thread, it remains smooth even during heavy React renders. Entering and exiting transitions can also be customized separately, but the core layout animation specifically handles positional and dimensional changes between renders.

WHEN TO USE IT: Use layout animations whenever React state causes views to move or resize and you want that transition to feel physical. Three places this shows up: first, an accordion that grows in height and pushes the content below it downward; second, a filterable list where items change order and need to glide to their new positions; third, a message bubble that expands as text wraps to a new line. If the change is state-driven rather than gesture-driven, layout animations give you declarative polish without manual measurement code.

WHEN NOT TO USE IT: Avoid layout animations on components that also use gesture handlers or manual shared values to control position, scale, or rotation. Both systems attempt to write to the same underlying transform matrix, which produces snapping, jitter, or ignored inputs. You should also skip them when layout changes fire on every frame, such as during a continuous drag, because starting a new layout transition each frame creates overlapping animations and visual noise. For purely cosmetic prop changes like border radius or opacity that do not affect layout, standard worklets are simpler.

ONE CANONICAL EXAMPLE: Consider a task list where tapping a row reveals a detail panel beneath the title. Without layout animations, you would need to measure the panel height after mount, store it in a shared value, and animate the container height from zero to that measured value. With Reanimated, you simply wrap the detail panel in an Animated.View and set its layout prop to Layout.springify(). When the panel mounts and the parent row's height increases, Reanimated automatically springs the row to its new bounds and shifts every subsequent list item downward in a single smooth motion.