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flutter_constraints

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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.
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<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.
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<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>