I’m having problems with my code inserting a "widget builder".
An error appears in the line key
builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
My code that is giving this failure is:
Widget build(BuildContext context) {
return StreamBuilder<QuerySnapshot>(
stream: FirebaseFirestore.instance.collection("Conversas").snapshots(),
builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
if (snapshot.hasError) {
return Center(
child: Text("Desculpe. Aconteceu algum erro de nossa parte. =(")
); //Center
}
if(snapshot.connectionState == ConnectionState.waiting){
return Center(
child: Text("Carregando")
); //Center
}
if(snapshot.hasData) {
return CustomScrollView(
slivers: [
CupertinoSliverNavigationBar(
largeTitle: Text('Conversas'),
), //CupertinoSliverNavigationBar
SliverList(
delegate: SliverChildListDelegate(
snapshot.data!.docs.map((DocumentSnapshot document){
return Container();
}).toList())) //SliverChildListDelegate, SliverList
],
); //CustomScrollView
}
}); //StreamBuilder
When I try to run the app, the log that appears in the console is:
Launching lib\main.dart on SM G780G in debug mode…
Running Gradle task ‘assembleDebug’…
lib/screens/conversas.dart:13:18: Error: A non-null value must be returned since the return type ‘Widget’ doesn’t allow null.
- ‘Widget’ is from ‘package:flutter/src/widgets/framework.dart’ (‘/C:/src/flutter/packages/flutter/lib/src/widgets/framework.dart’).
builder: (BuildContext context, AsyncSnapshot snapshot) {
^
FAILURE: Build failed with an exception.
-
Where:
Script ‘C:\src\flutter\packages\flutter_tools\gradle\flutter.gradle’ line: 1156 -
What went wrong:
Execution failed for task ‘:app:compileFlutterBuildDebug’.
Process ‘command ‘C:\src\flutter\bin\flutter.bat” finished with non-zero exit value 1
- Try:
Run with –stacktrace option to get the stack trace.
Run with –info or –debug option to get more log output.
Run with –scan to get full insights.
- Get more help at https://help.gradle.org
BUILD FAILED in 17s
Exception: Gradle task assembleDebug failed with exit code 1
>Solution :
Return a container or sized box at the end. If no condition is met then it’s null which is not a return type widget. But the method requires a widget to be returned so adding a return any widget at the end should resolve it
Widget build(BuildContext context) {
return StreamBuilder<QuerySnapshot>(
stream: FirebaseFirestore.instance.collection("Conversas").snapshots(),
builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
if (snapshot.hasError) {
return Center(
child: Text("Desculpe. Aconteceu algum erro de nossa parte. =(")
); //Center
}
if(snapshot.connectionState == ConnectionState.waiting){
return Center(
child: Text("Carregando")
); //Center
}
if(snapshot.hasData) {
return CustomScrollView(
slivers: [
CupertinoSliverNavigationBar(
largeTitle: Text('Conversas'),
), //CupertinoSliverNavigationBar
SliverList(
delegate: SliverChildListDelegate(
snapshot.data!.docs.map((DocumentSnapshot document){
return Container();
}).toList())) //SliverChildListDelegate, SliverList
],
); //CustomScrollView
}
return SizedBox.shrink();// add this. If it doesn't meet any condition then a sized box with no size is returned
}); //