Flutter：在FutureBuilder中增加索引<List?>

Question

我有一个问题，不知道如何在我的情况下正确使用 if 语句，我执行 sql 查询并返回数据，所以我创建了 If 语句，当 Needed-Scanned=0 时增加索引，

基本上它的意思是，当没有任何东西剩下时转到下一个数据，但它不起作用或在第一次迭代后结束。所以接下来我确实尝试使用 Setstate(){ Index ++; } 我有以下错误：

            Expanded(
                child: FutureBuilder<List?>(
                    future: read(  // "SELECT ProductAdress, ProductSeriesDescr+' ' ProductSeriesDescr, replace(ProductName, '\"', '')ProductName, NeedCount+'' NeedCount, ScanCount+'' ScanCount, ProductBarCode, ProductSeriesCount, ProductExpirationDate FROM ScanRest WHERE ProductStation = '${widget.nrStatie}' AND BoxID = '$cutieScan' Order By ProductName ASC"),
                        "SELECT ProductAdress, NeedCount+' ' NeedCount, ProductSeriesDescr+' ' ProductSeriesDescr, replace(ProductName, '\"', '')ProductName, ScanCount+' ' ScanCount, ProductSeriesCount+' ' ProductSeriesCount, ProductExpirationDate, ProductBarCode FROM ScanRest WHERE ProductStation = '${widget.nrStatie}' AND BoxID = '$cutieScan' Order By ProductAdress ASC"), // OrderDate = Cast(getdate() as date)
                    builder: (context, snapshot) {
                      switch (snapshot.connectionState) {
                        case ConnectionState.waiting:
                          return const Text('Loading....');
                        default:
                          if (snapshot.hasError) {
                            debugPrint("call error ${snapshot.error}"); //"call error = ${snapshot.error}"  
                            return Text('Error: ${snapshot.error}');
                          }
                          debugPrint(
                              "call success din sql"); // "call success = ${snapshot.data}"
                          List data = snapshot.data ?? [];
                          if (snapshot.data!.isEmpty) {
                            return Visibility(
                                visible: !vizibil,
                                child: Column(children: [
                                  const Text('Barcode gresit sau statie goala'),
                                  IconButton(
                                      onPressed: () {
                                        Navigator.push(context,
                                          MaterialPageRoute(
                                            builder: (context) => widget));
                                      },
                                      icon: const Icon(Icons.replay_outlined)),
                                ]));
                          }

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

                          if (int.parse((data[index]as Map)['NeedCount'].toString()) - int.parse((data[index]as Map)['ScanCount'].toString()) == 0){
                            index ++;
                            if(index == snapshot.data?.length){
                                Navigator.push( context,
                                  MaterialPageRoute( builder: (context) => dita_lista(
                                  nrStatie: widget.nrStatie,
                                  cutieScan: cutieScan,
                             )));

<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

                            }
                          }
                            debugPrint(index.toString());
                          return SingleChildScrollView(
                            child: Column(
                              children: [
                                const SizedBox(height: 10),
                                Row(
                                  children: [
                                    Expanded(
                                        flex: 3,
                                        child: Text((data[index]as Map)['ProductAdress'].toString(),textAlign: TextAlign.center,
                                          style: const TextStyle(fontSize: 40),)),