Could not launch Instance of 'Future<String>' - dart

Question

I have the following FutureBuilder function in class A:
Future<String> GetYoutubeLink() async{
var link = "";
CollectionReference collectionRef =
Firestore.instance.collection("r");
Query query = collectionRef.where('name',
isEqualTo: name).limit(1);
QuerySnapshot collectionSnapshot = await query.getDocuments().then((data){
if(data.documents.length > 0){
link = data.documents[0].data['link'];
print(link);
}
});
return link.toString();
}
}
I am trying to set the link in class B as follows:
class _B extends State<B> {
String link = null;
void initState(){
super.initState();
setState(() {
A a = new A(widget.dish_name);
if(link == null) {
link = a.GetYoutubeLink().toString();
}
});
}
#override
Widget build(BuildContext context) {
return Column(
mainAxisSize: MainAxisSize.min,
mainAxisAlignment: MainAxisAlignment.center,
children: [
IconButton(
icon: Icon(FontAwesomeIcons.youtubeSquare, size: 45,color:Colors.red),
onPressed: _launchURL,
),
],
);
}
_launchURL() async {
var url = link;
if (await canLaunch(url)) {
await launch(url);
} else {
throw 'Could not launch $url';
}
}
}
I am getting the following exception:
Could not launch Instance of 'Future'
Can someone tell me how to get the string instead of Future ?

Answer 1

Just Modify your code like this..
_launchURL() async{
CollectionReference collectionRef =
Firestore.instance.collection("r");
Query query = collectionRef.where('name',
isEqualTo: name).limit(1);
QuerySnapshot collectionSnapshot = await query.getDocuments().then((data){
if(data.documents.length > 0){
link = data.documents[0].data['link'];
if (await canLaunch(url)) {
await launch(url);
} else {
throw 'Could not launch $url';
}
}
});
}
And no need for initState() just remove that call.

Answer 2

Class a's method:
Future<String> getYoutubeLink() async {//its a good practice to set the method's name in lowerCamelCase
CollectionReference collectionRef = Firestore.instance.collection("r");
Query query = collectionRef.where('name', isEqualTo: name).limit(1);
QuerySnapshot collectionSnapshot = await query.getDocuments().then((data) {
try {
if (data.documents.length > 0) {
return data.documents[0].data['link'].toString(); //this will return the data as a string
}
} catch (e) {
return ""; //in case that something fails will return an empty string
}
});
return ""; //if it do not return anything will return an empty string
}
Class b:
class _B extends State<B> {
A a = new A(widget.dish_name);
#override
Widget build(BuildContext context) {
return Column(
mainAxisSize: MainAxisSize.min,
mainAxisAlignment: MainAxisAlignment.center,
children: [
IconButton(
icon: Icon(FontAwesomeIcons.youtubeSquare, size: 45,color:Colors.red),
onPressed: _launchURL,
),
],
);
}
_launchURL() async {
var url = await a.getYoutubeLink();//call here your method. You are useing 'await' because this methods returns a Future, it means that the execution of this function should take some time
if (await canLaunch(url)) {
await launch(url);
} else {
throw 'Could not launch $url';
}
}
}
Do not call Future methods inside your initState() because it would crash your app. If you need to call Future methods that need time to be completed before building your widget you can use the FutureBuilder widget. Check here the documentation.
To know more about Future and async programing watch this video by MTechViral. I have learned a lot from him!