Problem in receiving Future data (SharedPreferences) in Flutter - flutter

Question

I am trying to save the value of Switch in SharedPreferences. Here is my code :
bool isDarkTheme;
static const String KEY_DARK_THEME = "dark";
void setTheme(bool value) async {
SharedPreferences pref = await SharedPreferences.getInstance();
isDarkTheme = value;
pref.setBool(KEY_DARK_THEME, isDarkTheme);
print("DARKSet? $isDarkTheme");
}
void getTheme() async {
SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
isDarkTheme = sharedPreferences.getBool(KEY_DARK_THEME);
print("dark? $isDarkTheme");
}
#override
void initState() {
// TODO: implement initState
super.initState();
print("MYINIT");
getTheme();
}
And inside Build method...
#override
Widget build(BuildContext context) {
print("BUILD $isDarkTheme");
...
...
ListTile(
title: Text("Dark Theme"),
trailing: Switch(
value: isDarkTheme ?? false,
onChanged: (val) {
setState(() {
setTheme(val);
});
},
),
),
...
...
}
Though I get the correct value inside debug console, but Switch widget is not changed accordingly. I found build() method is run before getting the value from SharedPrefernces, as a result Switch widget is not getting value from SharedPreferences. How to solve this problem of receiving Future value?

Answer 1

You have two option
1). I think when you get value from SharedPreference at that time you just call setState() method
void getTheme() async {
SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
setState(() {
isDarkTheme = sharedPreferences.getBool(KEY_DARK_THEME);
print("dark? $isDarkTheme");
});}
2) You can use Provider for StateManagement so, when isDarkTheme value is changed notifyListener is called and your build method is rebuild and you see the change

Answer 2

Your main issue is that you're retrieving the SharedPreferences instance whenever you want to store or retrieve a value, beside the fact you're also using two instances of it (pref and sharedPreferences) :
retrieve a single SharedPreferences instance using a separate function:
SharedPreferences pref ;
Future loadPreferences() async {
pref = await SharedPreferences.getInstance();
}
Then modify getTheme and setTheme :
void setTheme(bool value) async {
isDarkTheme = value;
pref.setBool(KEY_DARK_THEME, isDarkTheme);
print("DARKSet? $isDarkTheme");
}
void getTheme() async {
isDarkTheme = pref.getBool(KEY_DARK_THEME);
print("dark? $isDarkTheme");
}
Also, call loadPreferences during initialization, so pref will be loaded by the time build is called:
#override
void initState() {
super.initState();
print("MYINIT");
loadPreferences().then((_){
getTheme();
});
}