BoxConstraints class

Immutable layout constraints for RenderBox layout.

A Size respects a BoxConstraints if, and only if, all of the following relations hold:

The constraints themselves must satisfy these relations:

double.infinity is a legal value for each constraint.

The box layout model

Render objects in the Flutter framework are laid out by a one-pass layout model which walks down the render tree passing constraints, then walks back up the render tree passing concrete geometry.

For boxes, the constraints are BoxConstraints, which, as described herein, consist of four numbers: a minimum width minWidth, a maximum width maxWidth, a minimum height minHeight, and a maximum height maxHeight.

The geometry for boxes consists of a Size, which must satisfy the constraints described above.

Each RenderBox (the objects that provide the layout models for box widgets) receives BoxConstraints from its parent, then lays out each of its children, then picks a Size that satisfies the BoxConstraints.

Render objects position their children independently of laying them out. Frequently, the parent will use the children's sizes to determine their position. A child does not know its position and will not necessarily be laid out again, or repainted, if its position changes.

Terminology

When the minimum constraints and the maximum constraint in an axis are the same, that axis is tightly constrained. See: new BoxConstraints.tightFor, new BoxConstraints.tightForFinite, tighten, hasTightWidth, hasTightHeight, isTight.

An axis with a minimum constraint of 0.0 is loose (regardless of the maximum constraint; if it is also 0.0, then the axis is simultaneously tight and loose!). See: new BoxConstraints.loose, loosen.

An axis whose maximum constraint is not infinite is bounded. See: hasBoundedWidth, hasBoundedHeight.

An axis whose maximum constraint is infinite is unbounded. An axis is expanding if it is tightly infinite (its minimum and maximum constraints are both infinite). See: new BoxConstraints.expand.

An axis whose minimum constraint is infinite is just said to be infinite (since by definition the maximum constraint must also be infinite in that case). See: hasInfiniteWidth, hasInfiniteHeight.

A size is constrained when it satisfies a BoxConstraints description. See: constrain, constrainWidth, constrainHeight, constrainDimensions, constrainSizeAndAttemptToPreserveAspectRatio, isSatisfiedBy.

Inheritance

Constructors

BoxConstraints({double minWidth: 0.0, double maxWidth: double.infinity, double minHeight: 0.0, double maxHeight: double.infinity })
Creates box constraints with the given constraints.
const
BoxConstraints.expand({double width, double height })
Creates box constraints that expand to fill another box constraints. [...]
const
BoxConstraints.loose(Size size)
Creates box constraints that forbid sizes larger than the given size.
BoxConstraints.tight(Size size)
Creates box constraints that is respected only by the given size.
BoxConstraints.tightFor({double width, double height })
Creates box constraints that require the given width or height. [...]
const
BoxConstraints.tightForFinite({double width: double.infinity, double height: double.infinity })
Creates box constraints that require the given width or height, except if they are infinite. [...]
const

Properties

biggest → Size
The biggest size that satisfies the constraints.
read-only
flipped → BoxConstraints
A box constraints with the width and height constraints flipped.
read-only
hasBoundedHeight → bool
Whether there is an upper bound on the maximum height. [...]
read-only
hasBoundedWidth → bool
Whether there is an upper bound on the maximum width. [...]
read-only
hashCode → int
The hash code for this object. [...]
read-only, override
hasInfiniteHeight → bool
Whether the height constraint is infinite. [...]
read-only
hasInfiniteWidth → bool
Whether the width constraint is infinite. [...]
read-only
hasTightHeight → bool
Whether there is exactly one height value that satisfies the constraints.
read-only
hasTightWidth → bool
Whether there is exactly one width value that satisfies the constraints.
read-only
isNormalized → bool
Returns whether the object's constraints are normalized. Constraints are normalized if the minimums are less than or equal to the corresponding maximums. [...]
read-only, override
isTight → bool
Whether there is exactly one size that satisfies the constraints.
read-only, override
maxHeight → double
The maximum height that satisfies the constraints. [...]
final
maxWidth → double
The maximum width that satisfies the constraints. [...]
final
minHeight → double
The minimum height that satisfies the constraints.
final
minWidth → double
The minimum width that satisfies the constraints.
final
smallest → Size
The smallest size that satisfies the constraints.
read-only
runtimeType → Type
A representation of the runtime type of the object.
read-only, inherited

Methods

constrain(Size size) → Size
Returns the size that both satisfies the constraints and is as close as possible to the given size. [...]
constrainDimensions(double width, double height) → Size
Returns the size that both satisfies the constraints and is as close as possible to the given width and height. [...]
constrainHeight([double height = double.infinity ]) → double
Returns the height that both satisfies the constraints and is as close as possible to the given height.
constrainSizeAndAttemptToPreserveAspectRatio(Size size) → Size
Returns a size that attempts to meet the following conditions, in order: [...]
constrainWidth([double width = double.infinity ]) → double
Returns the width that both satisfies the constraints and is as close as possible to the given width.
copyWith({double minWidth, double maxWidth, double minHeight, double maxHeight }) → BoxConstraints
Creates a copy of this box constraints but with the given fields replaced with the new values.
debugAssertIsValid({bool isAppliedConstraint: false, InformationCollector informationCollector }) → bool
Asserts that the constraints are valid. [...]
override
deflate(EdgeInsets edges) → BoxConstraints
Returns new box constraints that are smaller by the given edge dimensions.
enforce(BoxConstraints constraints) → BoxConstraints
Returns new box constraints that respect the given constraints while being as close as possible to the original constraints.
heightConstraints() → BoxConstraints
Returns box constraints with the same height constraints but with unconstrained width
isSatisfiedBy(Size size) → bool
Whether the given size satisfies the constraints.
loosen() → BoxConstraints
Returns new box constraints that remove the minimum width and height requirements.
normalize() → BoxConstraints
Returns a box constraints that isNormalized. [...]
tighten({double width, double height }) → BoxConstraints
Returns new box constraints with a tight width and/or height as close to the given width and height as possible while still respecting the original box constraints.
toString() → String
Returns a string representation of this object.
override
widthConstraints() → BoxConstraints
Returns box constraints with the same width constraints but with unconstrained height.
noSuchMethod(Invocation invocation) → dynamic
Invoked when a non-existent method or property is accessed. [...]
inherited

Operators

operator %(double value) → BoxConstraints
Computes the remainder of each constraint parameter by the given value.
operator *(double factor) → BoxConstraints
Scales each constraint parameter by the given factor.
operator /(double factor) → BoxConstraints
Scales each constraint parameter by the inverse of the given factor.
operator ==(dynamic other) → bool
The equality operator. [...]
override
operator ~/(double factor) → BoxConstraints
Scales each constraint parameter by the inverse of the given factor, rounded to the nearest integer.

Static Methods

lerp(BoxConstraints a, BoxConstraints b, double t) → BoxConstraints
Linearly interpolate between two BoxConstraints. [...]