Flutter development – data persistent storage shared_preferences

An overview

• shared_preferences，It saves data in the form of Key-Value（key-value pair），supports Android and iOS
• shared_preferences is a third-party plug-in ， use SharedPreferences in Android ， use NSUserDefaults

Second add dependency

2.1 Dependency address

• pub address：https://pub.flutter-io. cn/packages/shared_preferences
• Github address ：https://github.com/flutter/plugins/tree/master/packages/shared_preferences/shared_preferences

2.2 Add dependencies

Add dependencies in the pubspec.yaml file of the project

dependencies:shared_preferences: ^2.0.6


Execute command

flutter pub get


Three shared_preferences operations

3.1 Supported data types

The data types supported by shared_preferences are int, double, bool, string, stringList

3.2 shared_preferences instantiation

Synchronous operation

Future _prefs = SharedPreferences.getInstance();


Asynchronous operation (async)

var prefs = await SharedPreferences.getInstance();


3.3 Basic operation of data (int as an example)

3.3.1 Read Data

Future _readData() async {var prefs = await SharedPreferences.getInstance();var result &#61 ; prefs.getInt('Key_Int'); return result ?? 0;
}


3.3.2 Save data

_saveData() async {var prefs = await SharedPreferences.getInstance();prefs.setInt('Key_Int', 12);
}


3.3.3 Delete data

Future _deleteData() async {var prefs = await SharedPreferences.getInstance();prefs .remove('Key');
}


3.3.4 Clear all data

Future _clearData() async {var prefs = await SharedPreferences.getInstance();prefs.clear();
}


3.4 Key related operations

3.4.1 Get all Keys

Future<Set> _getKeys() async {var prefs = await SharedPreferences .getInstance();var keys = prefs.getKeys();return keys ?? [];
}


3.4.2 Check whether Does the Key exist

Future _containsKey() async {var prefs = await SharedPreferences.getInstance();return prefs.containsKey('Key') ? ? false;
}


Four examples

4.1 Code

Future _prefs = SharedPreferences.getInstance(); //sharepreference initialization
late Future _counter;//variables//in turn +1Future _incrementCounter() async {final SharedPreferences prefs & #61; await _prefs; final int counter = (prefs.getInt('counter') ?? 0) + 1;setState(() {_counter = prefs.setInt ("counter", counter).then((bool success) {return counter;});});}@override void initState() {super.initState();_counter = _prefs.then(( SharedPreferences prefs) {return (prefs.getInt('counter') ?? 0);});}body: Center(child: FutureBuilder(future: _counter,builder: (BuildContext context, AsyncSnapshot snapshot) {switch (snapshot.connectionState) {case ConnectionState.waiting:return const CircularProgressIndicator();default:if (snapshot.hasError) {return Text('Error: ${snapshot.error}'Error: ${snapshot.error}' 39;);} else {return Text('Button clicked ${snapshot.data} times',);}}})), floatingActionButton: FloatingActionButton(onPressed: _incrementCounter, tooltip: &#39 ;Increment',child: const Icon(Icons.add),),


4.2 renderings



4.3 View shared_preferences file

• Open Device File Explorer，Select Device，Find the data/data/com.example.flutter_image(package name)/shared_prefs folder

  

• Right click the FlutterSharedPreferences.xml file to export& #xff0c; Open to view file information