Error Dart/Flutter: 'context != null': is not true - firebase

Question

I am trying to apply a dialog alert every time the item is duplicated but when I do the test it ends up giving this error, does anyone have any tips on how to fix this?
void SalvarMensagem() async {
// select id_armarios from armarios where numero_serie = '$_numeroSerie'
this._status = _status;
_numeroSerie = _status.substring(48, 80);
final QuerySnapshot result = await Future.value(Firestore.instance
.collection("lockers")
.where("numero_serie", isEqualTo: "$_numeroSerie")
.limit(1)
.getDocuments());
final List<DocumentSnapshot> documents = result.documents;
if (documents.length == 1) {
duplicado(context);
} else {
await Firestore.instance
.collection("lockers")
.document()
.setData({"numero_serie": _numeroSerie});
}
}
duplicado(BuildContext context){
Alert(
context: context,
type: AlertType.error,
title: "QR Code já cadastrado",
buttons: [
DialogButton(
child: Text(
"OK",
style: TextStyle(color: Colors.white, fontSize: 20),
),
onPressed: () => Navigator.pop(context),
color: Colors.lightBlueAccent,
width: 120,
)
],
).show();
}
Error:
E/flutter ( 9129): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: 'package:flutter/src/widgets/localizations.dart': Failed assertion: line 446 pos 12: 'context != null': is not true.

Answer 1

duplicate(context, title, content) {
showDialog(
context: context,
builder: (BuildContext context) {
return AlertDialog(
title: new Text(
title,
),
content: Padding(
padding: const EdgeInsets.all(8.0),
child: new Text(
content,
),
),
actions: <Widget>[
new FlatButton(
child: new Text(
"OK",
style: TextStyle(color: Colors.white),
),
onPressed: () {
Navigator.of(context).pop();
},
color: Colors.lightBlueAccent,
),
],
);
},
);
}
Change your alert function and call it with duplicate(context,"QR Code já cadastrado","The content you wanted or delete it") it should be okay. You can change title and content with function parameters.