approachLayout

Creates an approach layout intended to help gradually approach the destination layout calculated in the lookahead pass.

Common

fun Modifier.approachLayout(
    isMeasurementApproachInProgress: (lookaheadSize: IntSize) -> Boolean,
    isPlacementApproachInProgress:
        Placeable.PlacementScope.(lookaheadCoordinates: LayoutCoordinates) -> Boolean =
        defaultPlacementApproachInProgress,
    approachMeasure:
        ApproachMeasureScope.(measurable: Measurable, constraints: Constraints) -> MeasureResult,
): Modifier

Creates an approach layout intended to help gradually approach the destination layout calculated in the lookahead pass. This can be particularly helpful when the destination layout is anticipated to change drastically and would consequently result in visual disruptions.

In order to create a smooth approach, an interpolation (often through animations) can be used in approachMeasure to interpolate the measurement or placement from a previously recorded size and/or position to the destination/target size and/or position. The destination size is available in ApproachMeasureScope as ApproachMeasureScope.lookaheadSize. And the target position can also be acquired in ApproachMeasureScope during placement by using LookaheadScope.localLookaheadPositionOf with the layout's Placeable.PlacementScope.coordinates. The sample code below illustrates how that can be achieved.

isMeasurementApproachInProgress signals whether the measurement is in progress of approaching destination size. It will be queried after the destination has been determined by the lookahead pass, before approachMeasure is invoked. The lookahead size is provided to isMeasurementApproachInProgress for convenience in deciding whether the destination size has been reached.

isMeasurementApproachInProgress indicates whether the position is currently approaching destination defined by the lookahead, hence it's a signal to the system for whether additional approach placements are necessary. isPlacementApproachInProgress will be invoked after the destination position has been determined by lookahead pass, and before the placement phase in approachMeasure.

Once both isMeasurementApproachInProgress and isPlacementApproachInProgress return false, the system may skip approach pass until additional approach passes are necessary as indicated by isMeasurementApproachInProgress and isPlacementApproachInProgress.

IMPORTANT: It is important to be accurate in isPlacementApproachInProgress and isMeasurementApproachInProgress. A prolonged indication of incomplete approach will prevent the system from potentially skipping approach pass when possible.