How to center a widget inside a column inside of a SingleChildScrollView - flutter

Question

I have this screen with a searchWidget on top and a list below it. But the list data comes after querying in the searchWidget, and while waiting for the data to be fetched i want to render a ActivityIndicator at the center of the screen. But the progress indicator doesn't seem to take the rest of the space of the screen and it's directly below the searchWidget, and if i wrap it inside an Expanded it gives an error
body: SingleChildScrollView(
physics: BouncingScrollPhysics(),
child: Column(
mainAxisSize: MainAxisSize.max,
children: [
SearchWidget(
hintText: 'Search',
textEditingController: _textEditingController,
onCancel: () {
setState(() {
_textEditingController.text = '';
data = [];
});
},
onSubmitted: (val) {
onSubmitted(val);
}),
_isLoading
? (Container(
child: Center(
child: CupertinoActivityIndicator(
radius: 15,
),
),
))
: (data.length == 0
? SizedBox()
: Padding(
padding:
const EdgeInsets.only(top: 8, right: 8, left: 8),
child: ListView.builder(
shrinkWrap: true,
physics: NeverScrollableScrollPhysics(),
itemCount: data.length,
itemBuilder: (ctx, i) =>
ListItem(item: data[i]),
),
))
],
),
),

Answer 1

Try Expanded:
_isLoading
? (Expanded(
child: Center(
child: CupertinoActivityIndicator(
radius: 15,
),
),
))

Answer 2

Put your CupertinoActivityIndicator inside a Column and use Spacer to put it in the middle of the screen. Just like this:
Column(
children: [
Spacer(),
Container(
child: Center(
child: CupertinoActivityIndicator(
radius: 15,
),
),
),
Spacer()
]
)