SpacingUnit class abstract

Abstract base class for spacing units used in margins, padding, and gaps.

SpacingUnit defines units that calculate spacing values (margins, padding, gaps) for elements within a layout container. Spacing units determine the whitespace around and between elements.

Spacing units can reference various layout properties:

  • Fixed pixel values
  • Viewport dimensions
  • Child element sizes
  • Constrained values with min/max bounds

Spacing units support mathematical operations and can be combined to create dynamic spacing expressions that respond to layout context.

Common uses include:

  • Fixed padding/margins (e.g., 8px, 16px)
  • Responsive spacing based on viewport size
  • Gaps between flex items
  • Dynamic padding based on content

Spacing is computed during layout after size constraints are known but before final positioning, allowing spacing to adapt to available space.

Example:

// Fixed spacing
final padding = SpacingUnit.fixed(16.0);

// Responsive spacing: 5% of viewport
final gap = SpacingUnit.viewportSize * 0.05;

// Constrained spacing with min/max
final adaptive = SpacingUnit.constrained(
  spacing: SpacingUnit.viewportSize * 0.02,
  min: SpacingUnit.fixed(8.0),
  max: SpacingUnit.fixed(32.0),
);
Implementers
Available extensions

Constructors

SpacingUnit()
Creates a const spacing unit.
const
SpacingUnit.calc(SpacingUnit a, SpacingUnit b, CalculationOperation operation)
Creates a calculated spacing unit combining two spacing units with an operation.
const
factory
SpacingUnit.childSize([Object? key])
Creates a spacing unit based on a child element's size.
const
factory
SpacingUnit.constrained({required SpacingUnit spacing, SpacingUnit min, SpacingUnit max})
Creates a constrained spacing with min/max bounds.
const
factory
SpacingUnit.fixed(double value)
Creates a fixed spacing with the specified value.
const
factory
SpacingUnit.relative(double factor)
Creates a relative spacing unit with the specified factor.
const
factory

Properties

hashCode → int
The hash code for this object.
no setterinherited
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited

Methods

clamp({SpacingUnit min = const SpacingFixed(0), SpacingUnit max = const SpacingFixed(double.infinity)}) → SpacingUnit

Available on SpacingUnit, provided by the SpacingUnitExtension extension

Constrains this spacing unit within the specified min and max bounds.
computeSpacing({required ParentLayout parent, required LayoutAxis axis, required double viewportSize}) → double
Computes the actual spacing value.
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
toCodeString() → String
Returns a code string representation of this spacing unit.
toString() → String
A string representation of this object.
inherited

Operators

operator *(Object other) → SpacingUnit

Available on SpacingUnit, provided by the SpacingUnitExtension extension

Multiplies two spacing units.
operator +(SpacingUnit other) → SpacingUnit

Available on SpacingUnit, provided by the SpacingUnitExtension extension

Adds two spacing units together.
operator -(SpacingUnit other) → SpacingUnit

Available on SpacingUnit, provided by the SpacingUnitExtension extension

Subtracts one spacing unit from another.
operator /(SpacingUnit other) → SpacingUnit

Available on SpacingUnit, provided by the SpacingUnitExtension extension

Divides one spacing unit by another.
operator ==(Object other) → bool
The equality operator.
inherited
operator unary-() → SpacingUnit

Available on SpacingUnit, provided by the SpacingUnitExtension extension

Negates this spacing unit (equivalent to 0 - this).

Static Methods

lerp(SpacingUnit a, SpacingUnit b, double t) → SpacingUnit
Linearly interpolates between two spacing units.

Constants

viewportSize → const SpacingUnit
Spacing equal to the viewport size along the axis.
zero → const SpacingUnit
Zero spacing.