Why is there an error with snapshot.data.length? - flutter

Question

I am trying to parse data from an API. For that, I am using FutureBuilder to list all the parsed data in a ListView.
I've performed a check for nullity of snapshot.data but I keep on getting this error in the segment snapshot.data.length, it says, The property 'length' can't be unconditionally accessed because the receiver can be 'null'. Try making the access conditional (using '?.') or adding a null check to the target ('!').
I've a similar error in the snapshot.data[i] section, which says The method '[]' can't be unconditionally invoked because the receiver can be 'null'. Try making the call conditional (using '?.') or adding a null check to the target ('!').
Here is my code's section of the same:
body: Container(
child: FutureBuilder(
future: getData('hello'),
builder: (context, snapshot) {
if (snapshot.data == null) {
return Container(
child: Text("Loading"),
);
}else{
return ListView.builder(
itemCount: snapshot.data.length,
itemBuilder: (context, i) {
return ListTile(
title: snapshot.data[i].partOfSpeech,
);
});
}
},
),
),
Here's getData(String s):
Future<List> getData(String s) async {
var response = await http
.get(Uri.https('api.dictionaryapi.dev', 'api/v2/entries/en_US/' + s));
var jsonData = jsonDecode(response.body)[0];
List<Data> data = [];
for (var x in jsonData["meanings"]) {
String definition = x["definitions"][0]["definition"];
Data d = Data(x["partOfSpeech"], definition);
data.add(d);
}
return data;
}

Answer 1

if u are using a new version of flutter (2.2.0 or above). first try adding a null check to the target ('!'). because of the null safety feature.
body: Container(
child: FutureBuilder(
future: getData('hello'),
builder: (context, snapshot) {
if (snapshot.data == null) {
return Container(
child: Text("Loading"),
);
}else{
return ListView.builder(
itemCount: snapshot.data!.length,
itemBuilder: (context, i) {
return ListTile(
title: snapshot.data[i].partOfSpeech,
);
});
}
},
),
),
then try specifying the FutureBuilder type to a List of Data type
body: Container(
child: FutureBuilder<List<Data>>(
future: getData('hello'),
builder: (context, snapshot) {
if (snapshot.data == null) {
return Container(
child: Text("Loading"),
);
}else{
return ListView.builder(
itemCount: snapshot.data.length,
itemBuilder: (context, i) {
return ListTile(
title: snapshot.data[i].partOfSpeech,
);
});
}
},
),
),

Answer 2

In continuation to this answer,
I found the solution to my problem. Apparently getData was not returning a List as intended. Instead, it was returning an Object.
Typecasting the Object to List solved the problem.
Here's the corrected code:
body: Container(
child: FutureBuilder(
future: getData('hello'),
builder: (context, snapshot) {
if (snapshot.data == null) {
return Container(
child: Text("Loading"),
);
}else{
//typecasting Object to List
var data = (snapshot.data as List<Data>).toList();
return ListView.builder(
itemCount: data.length,
itemBuilder: (context, i) {
return ListTile(
title: data[i].partOfSpeech,
);
});
}
},
),
),

Answer 3

Put 'AsyncSnapshot' before snapshot in the builder parameter.
builder: (context, AsyncSnapshot snapshot)

Answer 4

Since you are checking that snapshot.data is not null you can do the following to fix it.
body: Container(
child: FutureBuilder(
future: getData('hello'),
builder: (context, snapshot) {
if (snapshot.data == null) {
return Container(
child: Text("Loading"),
);
} else{
return ListView.builder(
itemCount: snapshot.data!.length,
itemBuilder: (context, i) {
return ListTile(
title: snapshot.data[i]!.partOfSpeech,
);
});
}
},
),
),

Answer 5

What you need to look at is the result of getData('hello')
Apparently, it does not return something that has a length property.