call a function of a parent widget each time when a child widget is rebuilt - flutter

Question

I have two classes.
CustomParentWidget
CustomChildWidget(which shows CircularProgressIndicator if loading and CentralisedAssetLoader id loaded)
Now i need My CustomParentWidget height should be changed after rendering CustomChildWidget..
It is achieved by adding
WidgetsBinding.instance
.addPostFrameCallback((_) => calculateMaxOptionHeight());
in initState of CustomParentWidget..
The problem here is CustomParentWidget is getting height of CircularProgressIndicator only..
Since CustomChildWidget return CircularProgressIndicator at first,
addPostFrameCallBack of CustomParentWidget thinks that ChildWidget has been Rendered and setting the Height to parent..
But i need addPostFrameCallBack to be called again when the CentralisedAssetLoader is also Rendered.
Is there a way to call a function whenever a child widget is rendered?
class CustomParentWidget extends StatefulWidget {
CustomParentWidget();
#override
_CustomParentWidgetState createState() =>
_CustomParentWidgetState();
}
class _CustomParentWidgetState
extends State<CustomParentWidget> {
double widgetHeight;
#override
initState() {
//calling the calculate Function after the Layout is Rendered
WidgetsBinding.instance
.addPostFrameCallback((_) => calculateMaxOptionHeight());
super.initState();
}
void calculateWidgetHeight() {
setState(){
widgetHeight = getWidgetHeight();
}
}
#override
Widget build(BuildContext context) {
return Container(
child: CustomChildWidget(height: widgetHeight),
);
}
}
class CustomChildWidget extends StatefulWidget {
CustomChildWidget({this.height});
#override
_CustomChildWidgetState createState() => _CustomChildWidgetState();
}
class _CustomChildWidgetState extends State<CustomChildWidget> {
double height;
double width;
bool isLoaded;
#override
void initState() {
isLoaded = false;
prepareData();
super.initState();
}
void prepareData() async {
try {
height = getheight();
width = getwidth();
} catch (error) {}
setState(() {
height = height;
width = width;
isLoaded = true;
});
}
#override
Widget build(BuildContext context) {
final screenMaxWidth = MediaQuery.of(context).size.width;
if (!isLoaded) {
return CircularProgressIndicator();
}
return Container(
width: min(screenMaxWidth, width),
height: height,
child: CentralisedAssetLoader(
fit: BoxFit.contain,
assetIdentifier: assetIdentifier,
),
);
}
}

Answer 1

You're really working against the grain of fast performant widget layout. See the basics about layout in https://flutter.dev/docs/development/ui/layout/constraints.
However, if you really don't mind slowing down a bit, you can write very flexible custom layouts with the package:boxy (https://pub.dev/packages/boxy).