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example 1 |
<code_start> |
container(color: red) |
<code_end> |
the screen is the parent of the container, and it |
forces the container to be exactly the same size as the screen. |
so the container fills the screen and paints it red. |
<topic_end> |
<topic_start> |
example 2 |
<code_start> |
container(width: 100, height: 100, color: red) |
<code_end> |
the red container wants to be 100 × 100, |
but it can’t, because the screen forces it to be |
exactly the same size as the screen. |
so the container fills the screen. |
<topic_end> |
<topic_start> |
example 3 |
<code_start> |
center( |
child: container(width: 100, height: 100, color: red), |
) |
<code_end> |
the screen forces the center to be exactly the same size |
as the screen, so the center fills the screen. |
the center tells the container that it can be any size it |
wants, but not bigger than the screen. now the container |
can indeed be 100 × 100. |
<topic_end> |
<topic_start> |
example 4 |
<code_start> |
align( |
alignment: Alignment.bottomRight, |
child: container(width: 100, height: 100, color: red), |
) |
<code_end> |
this is different from the previous example in that it uses |
align instead of center. |
align also tells the container that it can be any size it |
wants, but if there is empty space it won’t center the container. |
instead, it aligns the container to the bottom-right of the |
available space. |
<topic_end> |
<topic_start> |
example 5 |
<code_start> |
center( |
child: container( |
width: double.infinity, height: double.infinity, color: red), |
) |
<code_end> |
the screen forces the center to be exactly the |
same size as the screen, so the center fills the screen. |
the center tells the container that it can be any size it wants, |
but not bigger than the screen. the container wants to be |
of infinite size, but since it can’t be bigger than the screen, |
it just fills the screen. |
<topic_end> |
<topic_start> |
example 6 |
<code_start> |
center( |
child: container(color: red), |
) |
<code_end> |
the screen forces the center to be exactly the |
same size as the screen, so the center fills the screen. |
the center tells the container that it can be any |
size it wants, but not bigger than the screen. |
since the container has no child and no fixed size, |
it decides it wants to be as big as possible, |
so it fills the whole screen. |
but why does the container decide that? |
simply because that’s a design decision by those who |
created the container widget. it could have been |
created differently, and you have to read the |
container API documentation to understand |
how it behaves, depending on the circumstances. |
<topic_end> |
<topic_start> |
example 7 |
<code_start> |
center( |
child: container( |
color: red, |
child: container(color: green, width: 30, height: 30), |
), |
) |
<code_end> |
the screen forces the center to be exactly the same |
size as the screen, so the center fills the screen. |
the center tells the red container that it can be any size |
it wants, but not bigger than the screen. since the red |
container has no size but has a child, |
it decides it wants to be the same size as its child. |
the red container tells its child that it can be any size |
it wants, but not bigger than the screen. |
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