ConstraintSet

ConstraintSet is a component in the Android ConstraintLayout library that represents a complete set of constraints for views within a ConstraintLayout. It provides a programmatic way to capture, modify, and apply constraint configurations at runtime, enabling dynamic updates to a user interface without inflating new layouts.

A ConstraintSet stores the constraints for each view by its id, including connections between views, margins, bias, dimension behavior, and visibility. It can be created by cloning an existing layout using clone(ConstraintLayout) or by inflating from a layout resource with clone(Context, int). Once populated, constraints can be modified with a range of methods such as connect, clear, setMargin, setVisibility, setGoneMargin, setHorizontalBias, setVerticalBias, centerHorizontally, and centerVertically. After changes are made, the constraints are applied to a ConstraintLayout by calling applyTo.

Typical usage involves preparing two configurations that represent different UI states. For example, one ConstraintSet can encode a compact state and another an expanded state. You can switch between them at runtime, often with transitions or animations, by applying the target ConstraintSet to the layout. This enables smooth transitions between layouts in response to user actions, device orientation changes, or data updates. ConstraintSet is also commonly used with TransitionManager to animate constraint changes without rebuilding the view hierarchy.

Relation to MotionLayout: MotionLayout uses ConstraintSets as part of its transition framework, but ConstraintSet can be employed independently with ConstraintLayout to implement state changes and animations without leveraging MotionLayout. Limitations: ConstraintSet is a data structure for constraints and requires a ConstraintLayout to render the resulting layout; it does not by itself manage layout rendering or complex behaviors.