Datasets:

Ekhlass

/

flutter_constraints

like 1

A loose constraint is one that has a minimum

of zero and a maximum non-zero.

Some boxes loosen the incoming constraints,

meaning the maximum is maintained but the

minimum is removed, so the widget can have

a minimum width and height both equal to zero.

Ultimately, Center’s purpose is to transform

the tight constraints it received from its parent

(the screen) to loose constraints for its child

(the Container).

If you revisit Example 3,

the Center allows the red Container to be smaller,

but not bigger than the screen.

<topic_end>

<topic_start>

Unbounded constraints

info Note

You might be directed here if the framework

detects a problem involving box constraints.

The Flex section below might also apply.

In certain situations,

a box’s constraint is unbounded, or infinite.

This means that either the maximum width or

the maximum height is set to double.infinity.

A box that tries to be as big as possible won’t

function usefully when given an unbounded constraint and,

in debug mode, throws an exception.

The most common case where a render box ends up

with an unbounded constraint is within a flex box

(Row or Column),

and within a scrollable region

(such as ListView and other ScrollView subclasses).

ListView, for example,

tries to expand to fit the space available

in its cross-direction

(perhaps it’s a vertically-scrolling block and

tries to be as wide as its parent).

If you nest a vertically scrolling ListView

inside a horizontally scrolling ListView,

the inner list tries to be as wide as possible,

which is infinitely wide,

since the outer one is scrollable in that direction.

The next section describes the error you might

encounter with unbounded constraints in a Flex widget.

<topic_end>

<topic_start>

Flex

A flex box (Row and Column) behaves

differently depending on whether its

constraint is bounded or unbounded in

its primary direction.

A flex box with a bounded constraint in its

primary direction tries to be as big as possible.

A flex box with an unbounded constraint

in its primary direction tries to fit its children

in that space. Each child’s flex value must be

set to zero, meaning that you can’t use

Expanded when the flex box is inside

another flex box or a scrollable;

otherwise it throws an exception.

The cross direction

(width for Column or height for Row),

must never be unbounded,

or it can’t reasonably align its children.

<topic_end>