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final String explanation =
'The screen forces the Center to be exactly the same size as the screen, '
'so the Center fills the screen.'
'\n\n'
'The Center tells the Container that it can be any size it wants, but not bigger than the screen.'
'\n\n'
'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.'
'\n\n'
'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 documentation to understand how it behaves, depending on the circumstances. ';
@override
Widget build(BuildContext context) {
return Center(
child: Container(color: red),
);
}
}
class Example7 extends Example {
const Example7({super.key});
@override
final code = 'Center(\n'
' child: Container(color: red\n'
' child: Container(color: green, width: 30, height: 30)))';
@override
final String explanation =
'The screen forces the Center to be exactly the same size as the screen, '
'so the Center fills the screen.'
'\n\n'
'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.'
'\n\n'
'The red Container tells its child that it can be any size it wants, but not bigger than the screen.'
'\n\n'
'The child is a green Container that wants to be 30x30.'
'\n\n'
'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 color isn\'t visible, since the green Container entirely covers all of the red Container.';
@override
Widget build(BuildContext context) {
return Center(
child: Container(
color: red,
child: Container(color: green, width: 30, height: 30),
),
);
}
}
class Example8 extends Example {
const Example8({super.key});
@override
final code = 'Center(\n'
' child: Container(color: red\n'
' padding: const EdgeInsets.all(20),\n'
' child: Container(color: green, width: 30, height: 30)))';
@override
final String explanation =
'The red Container sizes itself to its children size, but it takes its own padding into consideration. '
'So it is also 30x30 plus padding. '
'The red color is visible because of the padding, and the green Container has the same size as in the previous example.';
@override
Widget build(BuildContext context) {
return Center(
child: Container(
padding: const EdgeInsets.all(20),
color: red,
child: Container(color: green, width: 30, height: 30),
),
);
}
}
class Example9 extends Example {
const Example9({super.key});
@override
final code = 'ConstrainedBox(\n'
' constraints: BoxConstraints(\n'
' minWidth: 70, minHeight: 70,\n'
' maxWidth: 150, maxHeight: 150),\n'
' child: Container(color: red, width: 10, height: 10)))';
@override
final String explanation =
'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.'
'\n\n'
'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.';