RangeMaintainingScrollPhysics class

Scroll physics that attempt to keep the scroll position in range when the contents change dimensions suddenly.

If the scroll position is already out of range, this attempts to maintain the amount of overscroll or underscroll already present.

If the scroll activity is animating the scroll position, sudden changes to the scroll dimensions are allowed to happen (so as to prevent animations from jumping back and forth between in-range and out-of-range values).

These physics should be combined with other scroll physics, e.g. BouncingScrollPhysics or ClampingScrollPhysics, to obtain a complete description of typical scroll physics. See applyTo.

Implementation details

Specifically, these physics perform two adjustments.

The first is to maintain overscroll when the position is out of range.

The second is to enforce the boundary when the position is in range.

If the current velocity is non-zero, neither adjustment is made. The assumption is that there is an ongoing animation and therefore further changing the scroll position would disrupt the experience.

If the extents haven't changed, then the overscroll adjustment is not made. The assumption is that if the position is overscrolled, it is intentional, otherwise the position could not have reached that position. (Consider ClampingScrollPhysics vs BouncingScrollPhysics for example.)

If the position itself changed since the last animation frame, then the overscroll is not maintained. The assumption is similar to the previous case: the position would not have been placed out of range unless it was intentional.

In addition, if the position changed and the boundaries were and still are finite, then the boundary isn't enforced either, for the same reason. However, if any of the boundaries were or are now infinite, the boundary is enforced, on the assumption that infinite boundaries indicate a lazy-loading scroll view, which cannot enforce boundaries while the full list has not loaded.

If the range was out of range, then the boundary is not enforced even if the range is not maintained. If the range is maintained, then the distance between the old position and the old boundary is applied to the new boundary to obtain the new position.

If the range was in range, and the boundary is to be enforced, then the new position is obtained by deferring to the other physics, if any, and then clamped to the new range.

Inheritance

Constructors

RangeMaintainingScrollPhysics({ScrollPhysics parent})
Creates scroll physics that maintain the scroll position in range.
const

Properties

allowImplicitScrolling bool
Whether a viewport is allowed to change its scroll position implicitly in response to a call to RenderObject.showOnScreen. [...]
read-only, inherited
dragStartDistanceMotionThreshold double
The minimum amount of pixel distance drags must move by to start motion the first time or after each time the drag motion stopped. [...]
read-only, inherited
hashCode int
The hash code for this object. [...]
read-only, inherited
maxFlingVelocity double
Scroll fling velocity magnitudes will be clamped to this value.
read-only, inherited
minFlingDistance double
The minimum distance an input pointer drag must have moved to to be considered a scroll fling gesture. [...]
read-only, inherited
minFlingVelocity double
The minimum velocity for an input pointer drag to be considered a scroll fling. [...]
read-only, inherited
parent ScrollPhysics
If non-null, determines the default behavior for each method. [...]
final, inherited
runtimeType Type
A representation of the runtime type of the object.
read-only, inherited
spring SpringDescription
The spring to use for ballistic simulations.
read-only, inherited
tolerance Tolerance
The tolerance to use for ballistic simulations.
read-only, inherited

Methods

adjustPositionForNewDimensions({ScrollMetrics oldPosition, ScrollMetrics newPosition, bool isScrolling, double velocity}) double
Describes what the scroll position should be given new viewport dimensions. [...]
override
applyBoundaryConditions(ScrollMetrics position, double value) double
Determines the overscroll by applying the boundary conditions. [...]
inherited
applyPhysicsToUserOffset(ScrollMetrics position, double offset) double
Used by DragScrollActivity and other user-driven activities to convert an offset in logical pixels as provided by the DragUpdateDetails into a delta to apply (subtract from the current position) using ScrollActivityDelegate.setPixels. [...]
inherited
applyTo(ScrollPhysics ancestor) RangeMaintainingScrollPhysics
If parent is null then return a ScrollPhysics with the same runtimeType where the parent has been replaced with the ancestor. [...]
override
buildParent(ScrollPhysics ancestor) ScrollPhysics
If parent is null then return ancestor, otherwise recursively build a ScrollPhysics that has ancestor as its parent. [...]
@protected, inherited
carriedMomentum(double existingVelocity) double
Returns the velocity carried on repeated flings. [...]
inherited
createBallisticSimulation(ScrollMetrics position, double velocity) Simulation
Returns a simulation for ballistic scrolling starting from the given position with the given velocity. [...]
inherited
noSuchMethod(Invocation invocation) → dynamic
Invoked when a non-existent method or property is accessed. [...]
inherited
recommendDeferredLoading(double velocity, ScrollMetrics metrics, BuildContext context) bool
Provides a heuristic to determine if expensive frame-bound tasks should be deferred. [...]
inherited
shouldAcceptUserOffset(ScrollMetrics position) bool
Whether the scrollable should let the user adjust the scroll offset, for example by dragging. [...]
inherited
toString() String
Returns a string representation of this object.
inherited

Operators

operator ==(Object other) bool
The equality operator. [...]
inherited