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The screen forces the Center to be exactly the same
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size as the screen, so the Center fills the screen.The Center tells the red Container that it can be any size
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it wants, but not bigger than the screen. Since the red
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Container has no size but has a child,
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it decides it wants to be the same size as its child.The red Container tells its child that it can be any size
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it wants, but not bigger than the screen.The child is a green Container that wants to
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be 30 × 30. Given that the red Container sizes itself to
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the size of its child, it is also 30 × 30.
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The red color isn’t visible because the green Container
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entirely covers the red Container.<topic_end>
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<topic_start>Example 8
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<code_start>Center(
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child: Container(
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padding: const EdgeInsets.all(20),
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color: red,
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child: Container(color: green, width: 30, height: 30),
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),
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)<code_end>
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The red Container sizes itself to its children’s size,
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but it takes its own padding into consideration.
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So it is also 30 × 30 plus padding.
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The red color is visible because of the padding,
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and the green Container has the same size as
|
in the previous example.<topic_end>
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<topic_start>Example 9
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<code_start>ConstrainedBox(
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constraints: const BoxConstraints(
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minWidth: 70,
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minHeight: 70,
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maxWidth: 150,
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maxHeight: 150,
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),
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child: Container(color: red, width: 10, height: 10),
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)<code_end>
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You might guess that the Container has to be
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between 70 and 150 pixels, but you would be wrong.
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The ConstrainedBox only imposes additional constraints
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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
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constraints parameter.<topic_end>
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<topic_start>Example 10
|
<code_start>Center(
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child: ConstrainedBox(
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constraints: const BoxConstraints(
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minWidth: 70,
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minHeight: 70,
|
maxWidth: 150,
|
maxHeight: 150,
|
),
|
child: Container(color: red, width: 10, height: 10),
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),
|
)<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.
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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,
|
),
|
child: Container(color: red, width: 100, height: 100),
|
),
|
)<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 100 pixels, and that’s the size it has,
|
since that’s between 70 and 150.<topic_end>
|
<topic_start>Example 13
|
<code_start>UnconstrainedBox(
|
child: Container(color: red, width: 20, height: 50),
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)<code_end>
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The screen forces the UnconstrainedBox to be exactly
|
the same size as the screen. However, the UnconstrainedBox
|
lets its child Container be any size it wants.<topic_end>
|
<topic_start>Example 14
|
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