How I can exit from next line code in flutter - flutter

Question

I have a function:
onTap: () {
FunctionsClass.checkToken(context);
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => AttackDetailScreen(
idAttack:
data[index]['id'].toString())));
},
Checktoken function:
static Future<http.Response> checkToken(BuildContext context) async {
SharedPreferences prefs = await SharedPreferences.getInstance();
var url = kUrlAPI + 'checkToken/';
var response = await http.get(Uri.encodeFull(url),
headers: {
"Content-Type": "application/json",
'Authorization': 'Bearer ' + prefs.getString('token'),
});
var convertDataToJson = jsonDecode(response.body);
if(convertDataToJson['code'] == 401){
Loader.hide();
showDialog(
barrierDismissible: false,
context: context,
builder: (BuildContext context) => CustomDialog(
pressedAction: () {
Navigator.of(context).pop();
},
type: 'w',
title: kWarningTitle,
description: kGenericError,
buttonText: kCloseText,
),
);
//exit for next function
}
}
I want if convertDataToJson['code'] == 401, show dialog and not execute Navigator.
Something to not execute the next method

Answer 1

Return a value from your checkToken function that indicates whether the navigator should push or not. For example you can return null in case of an error or simply return boolean where true means push or false means don't push (or you could return the error string and check it inside onTap if you prefer that).
Let's assume you choose to return null if the navigator shouldn't push the page, then you can do this:
onTap: () {
FunctionsClass.checkToken(context).then((value) {
if(value == null) {
return; // don't do anything
} else {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => AttackDetailScreen(idAttack: data[index]['id'].toString())));
}
}
}

Answer 2

Try using try/catch for unexpected error too. And 'throw' a custom error.
This is consider a good practice.
static Future<http.Response> checkToken(BuildContext context) async {
SharedPreferences prefs = await SharedPreferences.getInstance();
var url = kUrlAPI + 'checkToken/';
try {
var response = await http.get(Uri.encodeFull(url),
headers: {
"Content-Type": "application/json",
'Authorization': 'Bearer ' + prefs.getString('token'),
});
var convertDataToJson = jsonDecode(response.body);
if(convertDataToJson['code'] == 401){
//exit for next function
throw Exception('some error');
}
} catch (error) {
throw error;
}
}
And use ".then" and '.catchError' while calling a Future function.
onTap: () {
FunctionsClass.checkToken(context).then((_) {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => AttackDetailScreen(
idAttack:
data[index]['id'].toString(),
),
),
);
}).catchError((onEroor){
Loader.hide();
showDialog(
barrierDismissible: false,
context: context,
builder: (BuildContext context) => CustomDialog(
pressedAction: () {
Navigator.of(context).pop();
},
type: 'w',
title: kWarningTitle,
description: kGenericError,
buttonText: kCloseText,
),
);
};
},