Flutter: ListView not displaying anything + lazy loading - flutter

Question

I am new in flutter and trying to create a listview with load more functionality.
Here is my class. It is not displaying anything, blank screen. List has data I am getting result in console.
class ReportPurchaseNew extends StatefulWidget {
final AdminUserDetails userDetails;
final String title;
const ReportPurchaseNew({Key key, this.title, this.userDetails})
: super(key: key);
#override
State<StatefulWidget> createState() => new ReportPurchaseState();
}
class ReportPurchaseState extends State<ReportPurchaseNew> {
String fromDate = "", toDate = "", usageType = "";
int limit = 7, offset = 0;
static int page = 0;
List<Result> _List = new List();
List<Result> _filteredList;
Future<PurchaseReport> _PurchaseReportResponse;
List<UsageResult> _usageList = [];
UsageResult _usageVal;
ScrollController _sc = new ScrollController();
bool isLoading = false;
//List users = new List();
#override
void initState() {
this._getMorePurchase(page);
super.initState();
_sc.addListener(() {
if (_sc.position.pixels ==
_sc.position.maxScrollExtent) {
_getMorePurchase(page);
}
});
}
#override
void dispose() {
_sc.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text("Lazy Load Large List"),
),
body: Container(
child: _buildList(),
),
resizeToAvoidBottomInset: false,
);
}
Widget _buildList() {
return ListView.builder(
itemCount: _List.length + 1, // Add one more item for progress indicator
padding: EdgeInsets.symmetric(vertical: 8.0),
itemBuilder: (BuildContext context, int index) {
if (index == _List.length) {
return _buildProgressIndicator();
} else {
return new ListTile(
leading: CircleAvatar(
radius: 30.0,
),
title :Text("my:"+(_List[index]
.product)),
subtitle: Text((_List[index]
.unitPrice)),
);
}
},
controller: _sc,
);
}
Widget _buildProgressIndicator() {
return new Padding(
padding: const EdgeInsets.all(8.0),
child: new Center(
child: new Opacity(
opacity: isLoading ? 1.0 : 00,
child: new CircularProgressIndicator(),
),
),
);
}
Future<PurchaseReport> getProjectDetails() async {
var result = await PurchaseReportRequest(
context,
widget.userDetails.result.raLoginId,
limit.toString(),
offset.toString(),
fromDate,
toDate,
_usageVal!=null ? _usageVal.name : "" ,
);
return result;
}
void _getMorePurchase(int index) async {
if (!isLoading) {
setState(() {
isLoading = true;
});
_PurchaseReportResponse = getProjectDetails();
setState(() {
isLoading = false;
_PurchaseReportResponse.then((response) {
if (response != null) {
_List.addAll(response.result);
page = page + limit;
print("printing length : "
+_List.length.toString());
for (int i = 0; i < response.result.length; i++) {
print('name:' +_List[i].product );
}
} else {
errorRaisedToast(context);
}
});
});
}
}
}

Answer 1

Try This,
if (response != null) {
List newList = new List();
// _List.addAll(response.result);
page = page + limit;
print("printing length : "
+_List.length.toString());
for (int i = 0; i < response.result.length; i++) {
newList.add(response.result[i]);
print('name:' +_List[i].product);
}
isLoading = false;
_List.addAll(newList);
page++;
} else {
errorRaisedToast(context);
}