title: Flutter - Delaying json requests to do once per time
body: <p>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.</p>
  
  <p>my list code:</p>
  
  <pre><code>new CustomScrollView(
            cacheExtent: height * 6,
              slivers: [
                new SliverList(
                    delegate: new SliverChildListDelegate(
                      [
                        new RelatorioVendPeriodoAPeriodo(),
                        new RelatorioMensals(),
                        new RelatorioDiasDaSemanas(),
                        new RelatorioVendasTotalidasPorPeriodo(),
                        new RelatorioDasVendasTotsProdutos(),
                      ]
                    )
                )
              ]
          ),
  </code></pre>
  
  <p>this new classes calls, returns for me request. Anyone knows how to delay it?</p>