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to space out list items evenly when there is enough space, and to allow
users to scroll when there is not enough space,
using the following steps:
<topic_end>
<topic_start>
1. add a LayoutBuilder with a SingleChildScrollView
start by creating a LayoutBuilder. you need to provide
a builder callback function with two parameters:
in this recipe, you won’t be using the BuildContext,
but you will need the BoxConstraints in the next step.
inside the builder function, return a SingleChildScrollView.
this widget ensures that the child widget can be scrolled,
even when the parent container is too small.
<code_start>
LayoutBuilder(builder: (context, constraints) {
return SingleChildScrollView(
child: placeholder(),
);
});
<code_end>
<topic_end>
<topic_start>
2. add a ConstrainedBox inside the SingleChildScrollView
in this step, add a ConstrainedBox
as the child of the SingleChildScrollView.
the ConstrainedBox widget imposes additional constraints to its child.
configure the constraint by setting the minHeight parameter to be
the maxHeight of the LayoutBuilder constraints.
this ensures that the child widget
is constrained to have a minimum height equal to the available
space provided by the LayoutBuilder constraints,
namely the maximum height of the BoxConstraints.
<code_start>
LayoutBuilder(builder: (context, constraints) {
return SingleChildScrollView(
child: ConstrainedBox(
constraints: BoxConstraints(minHeight: constraints.maxHeight),
child: placeholder(),
),
);
});
<code_end>
however, you don’t set the maxHeight parameter,
because you need to allow the child to be larger
than the LayoutBuilder size,
in case the items don’t fit the screen.
<topic_end>
<topic_start>
3. create a column with spaced items
finally, add a column as the child of the ConstrainedBox.
to space the items evenly,
set the mainAxisAlignment to MainAxisAlignment.spaceBetween.
<code_start>
LayoutBuilder(builder: (context, constraints) {
return SingleChildScrollView(
child: ConstrainedBox(
constraints: BoxConstraints(minHeight: constraints.maxHeight),
child: column(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
ItemWidget(text: 'item 1'),
ItemWidget(text: 'item 2'),
ItemWidget(text: 'item 3'),
],
),
),
);
});
<code_end>
alternatively, you can use the spacer widget
to tune the spacing between the items,
or the expanded widget, if you want one widget to take more space than others.
for that, you have to wrap the column with an IntrinsicHeight widget,
which forces the column widget to size itself to a minimum height,
instead of expanding infinitely.
<code_start>
LayoutBuilder(builder: (context, constraints) {
return SingleChildScrollView(
child: ConstrainedBox(
constraints: BoxConstraints(minHeight: constraints.maxHeight),
child: IntrinsicHeight(
child: column(
children: [
ItemWidget(text: 'item 1'),
spacer(),
ItemWidget(text: 'item 2'),
expanded(
child: ItemWidget(text: 'item 3'),
),
],
),
),
),
);
});
<code_end>
lightbulb tip
play around with different devices, resizing the app,
or resizing the browser window, and see how the item list adapts
to the available space.