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the child is a green container that wants to
be 30 × 30. given that the red container sizes itself to
the size of its child, it is also 30 × 30.
the red color isn’t visible because the green container
entirely covers the red container.
<topic_end>
<topic_start>
example 8
<code_start>
center(
child: container(
padding: const EdgeInsets.all(20),
color: red,
child: container(color: green, width: 30, height: 30),
),
)
<code_end>
the red container sizes itself to its children’s size,
but it takes its own padding into consideration.
so it is also 30 × 30 plus padding.
the red color is visible because of the padding,
and the green container has the same size as
in the previous example.
<topic_end>
<topic_start>
example 9
<code_start>
ConstrainedBox(
constraints: const BoxConstraints(
minWidth: 70,
minHeight: 70,
maxWidth: 150,
maxHeight: 150,
),
child: container(color: red, width: 10, height: 10),
)
<code_end>
you might guess that the container has to be
between 70 and 150 pixels, but you would be wrong.
the ConstrainedBox only imposes additional constraints
from those it receives from its parent.
here, the screen forces the ConstrainedBox to be exactly
the same size as the screen, so it tells its child container
to also assume the size of the screen, thus ignoring its
constraints parameter.
<topic_end>
<topic_start>
example 10
<code_start>
center(
child: ConstrainedBox(
constraints: const BoxConstraints(
minWidth: 70,
minHeight: 70,
maxWidth: 150,
maxHeight: 150,
),
child: container(color: red, width: 10, height: 10),
),
)
<code_end>
now, center allows ConstrainedBox to be any size up to
the screen size. the ConstrainedBox imposes additional
constraints from its constraints parameter onto its child.
the container must be between 70 and 150 pixels.
it wants to have 10 pixels,
so it ends up having 70 (the minimum).
<topic_end>
<topic_start>
example 11
<code_start>
center(
child: ConstrainedBox(
constraints: const BoxConstraints(
minWidth: 70,
minHeight: 70,
maxWidth: 150,
maxHeight: 150,
),
child: container(color: red, width: 1000, height: 1000),
),
)
<code_end>
center allows ConstrainedBox to be any size up to the
screen size. the ConstrainedBox imposes additional
constraints from its constraints parameter onto its child.
the container must be between 70 and 150 pixels.
it wants to have 1000 pixels,
so it ends up having 150 (the maximum).
<topic_end>
<topic_start>
example 12
<code_start>
center(
child: ConstrainedBox(
constraints: const BoxConstraints(
minWidth: 70,
minHeight: 70,
maxWidth: 150,
maxHeight: 150,