Trigger snackbar message on page load in Flutter - flutter

Question

I am new to Flutter and trying to trigger a snack bar on page load if a message was returned from the page I navigated from. I have managed to get the message to display on a button click, but get an error stating that my context does not have a Scaffold if I try to do it elsewhere.
I am also struggling to find an example of how to show a sack bar without user interaction, so if anyone has a reference, that would surely go a long way in helping as well.
Here is a simplified version of my view:
class LandingView extends StatefulWidget {
final LandingViewModel viewModel;
LandingView(this.viewModel);
#override
State<StatefulWidget> createState() {
return new _ViewState();
}
}
class _ViewState extends State<LandingView> {
#override
void initState() {
super.initState();
}
void _showSnackbar(context, message) {
final snackBar = SnackBar(
content: Text(message),
);
Scaffold.of(context).showSnackBar(snackBar);
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: SafeArea(
child: new GestureDetector(
onTap: () {
FocusScope.of(context).requestFocus(new FocusNode());
},
child: _buildLayout(context),
),
),
);
}
Widget _buildLayout(BuildContext context) {
Map<String, dynamic> args = getArgs(context); //get value from previous page
if (args != null &&
args["Toast Message"] != null) //check if a value was returned from the previous page. This has been tested and a valid string is being returned
_showSnackbar(
context, args["Toast Message"]); //if so call snack bar function
// this throws an error saying "Scaffold.of() called with a context that does not contain a Scaffold"
return LayoutBuilder(
builder: (BuildContext context, BoxConstraints boxConstraints) {
return SingleChildScrollView(
child: ConstrainedBox(
constraints: BoxConstraints(minHeight: boxConstraints.maxHeight),
child: RaisedButton(
child: Text(
"Show Snack Bar",
),
onPressed:
() {
if (args != null &&
args["Toast Message"] !=
null) //check if a value was returned from the previous page. This has been tested and a valid string is being returned
_showSnackbar(context,
args["Toast Message"]); //if so call snack bar function
//this works perfectly
}),
),
);
});
}
}
Any advice would be greatly appreciated

Answer 1

You're getting that because your LandingView widget is not in a Scaffold. You can fix this by putting the LandingView widget inside a StatelessWidget with a Scaffold and changing any references to LandingView to LandingViewPage:
class LandingViewPage extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
body: LandingView()
);
}
}

Answer 2

We can do this with addPostFrameCallback method
#override
void initState(){
super.initState();
WidgetsBinding.instance
.addPostFrameCallback((_) => scaffold.showSnackBar(SnackBar(content: Text("snackbar")));
}

Answer 3

In a stateful widget put:
#override
void initState() {
super.initState();
WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
ScaffoldMessenger.of(context).showSnackBar(
const SnackBar(content: Text("Error")));
});
}