There could be a time where you need to just save a simple value, like a boolean, a string or even an integer. This very easy task can result in useless complications if you save it into a file or into a database. Small & easy tasks should let you use easy and quick solutions. Let’s introduce shared_preferences then!
Android and iOS have different ways to perma-save small data, Android has SharedPreferences class, which represents an app-managed XML file (ore more files) with key-value elements, also they can be shared across other applications. UserDefaults is iOS way to store simple data, representing a simple synchronous database with cache features.
Flutter doesen’t have a built-in way to access these interfaces but a plugin directly created by Flutter Developers comes on our aid: shared_preferences. This simple plugin will let you use SharedPreferences and UserDefaults without worrying about the platform your app is running on! Let’s see a simple example to know better how to use it!
Here we have a simple app with a textbox, 2 buttons and a text. We want to save the input witha button and show it with the other button.
final textController = TextEditingController();
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
backgroundColor: Colors.red,
title: Text('Some Awesome Flutter App'),
),
body: Center(
child: Column(
crossAxisAlignment: CrossAxisAlignment.center,
mainAxisAlignment: MainAxisAlignment.center,
children: [
SizedBox(
width: 300,
child: TextField(
controller: textController,
decoration: InputDecoration(
border: OutlineInputBorder(
borderSide: BorderSide(color: Colors.black, width: 1.0),
),
hintText: 'Enter some data'
),
),
),
RaisedButton(
child: Text('Save', style: TextStyle(color: Colors.white)),
onPressed: null
),
RaisedButton(
child: Text('Show', style: TextStyle(color: Colors.white)),
onPressed: null
),
Text(
''
)
],
)
)
);
}Let’s give our ‘Save’ button some action by populating its onPressed method:
RaisedButton(
child: Text('Save', style: TextStyle(color: Colors.white)),
onPressed: () => saveText()
),
void saveText(){
String text = textController.text;
//Here we'll save our text
}Our saveText method can be now populated with shared_preferences methods.
First thing first, we need to istantiate our class, then just wait that it writes our data with an async method: setString. SharedPreference object have different methods for different type of data: setInt, setBool… even setStringList. We also wish to print if the data is saved correctly, any “set” method return a Future<bool> so we know if everything goes well. Let’s give our text as key “OurText”.
Our code will become:
RaisedButton(
child: Text('Save', style: TextStyle(color: Colors.white)),
onPressed:() async {
print(await saveText());
},
),
Future<bool> saveText() async{
String text = textController.text;
SharedPreferences prefs = await SharedPreferences.getInstance();
return prefs.setString('OurText', text);
}Writing something on our TextField, then clicking “save” will result then in:
[+12369 ms] I/flutter ( 9987): trueNow we should show our text. Time to work on ‘Show’ button:
Like saving we instantiate SharedPreferences then get our string with… getString (applause…). SharedPreferences.getInstance() is a future so we’ll need to get our String in a async method:
String ourText = '';
RaisedButton(
child: Text('Show', style: TextStyle(color: Colors.black)),
onPressed: () async {
ourText = await getText();
setState(() {
});
},
),
Text(
ourText
)
Future<String> getText() async{
SharedPreferences prefs = await SharedPreferences.getInstance();
return prefs.getString('OurText');
}And there we have:
Our text now is saved on SharedPreferences and UserDefaults, so even if we kill the app we can still show it without writing it down.
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