Flutter - Delaying json requests to do once per time - json

Question

i'm trying to do a Dashboard with multiples jsons requests, but i want that request work one per one, like when finish first request start the second, when finish second start the third when finish third start the N.
my list code:
new CustomScrollView(
cacheExtent: height * 6,
slivers: [
new SliverList(
delegate: new SliverChildListDelegate(
[
new RelatorioVendPeriodoAPeriodo(),
new RelatorioMensals(),
new RelatorioDiasDaSemanas(),
new RelatorioVendasTotalidasPorPeriodo(),
new RelatorioDasVendasTotsProdutos(),
]
)
)
]
),
this new classes calls, returns for me request. Anyone knows how to delay it?

Answer 1

First, the parent widget should return a progress bar when the necessary data is not available.
A service will be called an initState to fetch data from the backend. when data is ready setState() will be called to redraw the widget.
Look at this example:
class _TestWidgetState extends State<TestWidget> {
var data;
#override
void initState() {
data = NetworkService.getData().then((data) {
setState(() {
this.data = data;
});
});
}
#override
Widget build(BuildContext context) {
if (data == null) {
return CircularProgressIndicator();
} else {
return
new CustomScrollView(
cacheExtent: height * 6,
slivers: [
new SliverList(
delegate: new SliverChildListDelegate(
[
new RelatorioVendPeriodoAPeriodo(data: data),
new RelatorioMensals(data: data),
new RelatorioDiasDaSemanas(data: data),
new RelatorioVendasTotalidasPorPeriodo(data: data),
new RelatorioDasVendasTotsProdutos(data: data),
]
)
)
]
);
}
}
}
class NetworkService {
final JsonDecoder _decoder = new JsonDecoder();
static String data1;
static String data2;
static getData() async {
if (data1 == null || data2 == null) {
await fetchFromServer();
}
return {'data1': data1, 'data2': data2};
}
static fetchFromServer() async {
data1 = (await http.get('url')).body;
data2 = (await http.get('url')).body;
}
}

Answer 2

Future.delayed(const Duration(milliseconds: 500), () {
print(" This line is executed after 5 seconds");
});