Today to introduce you is the local storage method, it and The Android SharedPreferences in the same effect, the use is very simple, and finally I will package it into a tool class, for everyone to use, the next look at my simple introduction ~

  • What is a shared_preferences
  • Rely on
  • Guide package
  • Simple to use
  • Shared_preferences tools

What is a shared_preferences

SharedPreferences SharedPreferences is a storage tool that is commonly used to store local data in the form of key and value pairs. Since it is also a time-consuming operation, it must be identified with async,await

Rely on

Dependencies: shared_preferences: ^ 0.5.12 + 4

Guide package

The import ‘package: shared_preferences/shared_preferences dart “;

Simple to use

void setString(String key, String value) async {
    /** * Get the SharedPreferences instance */
    SharedPreferences instance = await SharedPreferences.getInstance();
    instance.setString(key, value);
  }
  

  Future<String> getString(String key) async {
    /** * Get the SharedPreferences instance */
    SharedPreferences instance = await SharedPreferences.getInstance();
    return instance.getString(key);
  }
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Okay, so there’s nothing to say about this code, except that it’s set,get, okay

Shared_preferences also provides several methods for assigning different values:





Use the same as setString!

Shared_preferences provides a set of values, and there must be a way to get the values. Here are a few ways to get the values



As with getString(), you just pass in the key value

Shared_preferences also provides the remove method

/** * Delete the value */ corresponding to key
  remove(String key) async{
    SharedPreferences instance= await SharedPreferences.getInstance();
    instance.remove(key);
  }
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Take a look at the full code:

import 'package:flutter/material.dart';
import 'package:flutter_trip/util/sp_util.dart';
import 'package:shared_preferences/shared_preferences.dart';

class SPTest extends StatefulWidget {
  @override
  _SPTestState createState(a) => _SPTestState();
}

class _SPTestState extends State<SPTest> {
  String TEST_KEY = "test_key";
  String _mObtainData = "";
   final TextEditingController _textcontroller  = TextEditingController();
  @override
  Widget build(BuildContext context) {
    
    getString(TEST_KEY).then((value) {
      _mObtainData = value;
      print("${value}");
    });

    return Column(
      children: [
        TextField(
          controller: _textcontroller ,
          decoration: InputDecoration(
            hintText: "Please enter a stored value",
            suffixIcon: IconButton(
              icon: Icon(Icons.delete),
              onPressed: (){
                /** * refresh Build and reassign */ to the following Text

                setState(() {
                // delete the saved text in sp
                  remove(TEST_KEY);
                  // Delete the text on the keyboard
                  _textcontroller.clear();
                });

              },
            )
          ),
          onChanged: (value) {
            /** * refresh Build and reassign */ to the following Text
            setState(() {
              setString(TEST_KEY, value);
            });
          },
        ),
        Text("Stored data :\n${_mObtainData}",textAlign: TextAlign.center,style: TextStyle(fontSize: 30),),,); }void setString(String key, String value) async {
    /** * Get the SharedPreferences instance */
    SharedPreferences instance = await SharedPreferences.getInstance();
    instance.setString(key, value);
  }

  Future<String> getString(String key) async {
    /** * Get the SharedPreferences instance */
    SharedPreferences instance = await SharedPreferences.getInstance();
    return instance.get(key);
  }

  /** * Delete the value */ corresponding to Key
  static remove(String key) async{ SharedPreferences instance= await SharedPreferences.getInstance(); instance.remove(key); }}Copy the code

Effect:

Take a look at log:

Comments written very detailed, not verbose, next it Sp package, to provide everyone to use

Shared_preferences tools

import 'package:shared_preferences/shared_preferences.dart'; / / rely on address: https://pub.dev/packages/shared_preferences / * * * SZJ 2020/11/20 * / class SpUtil {/ / / by / / / stored value in the form of generics -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- - / / / -- -- -- -- -- -- -- -- -- -- he has to write a generic!!!!!!!!!! ---------- /// --------------------------------- static setData<T>(String key, T value) async { SharedPreferences instance = await SharedPreferences.getInstance(); switch (T) { case String: print("SpUtilsetData:T:${T}\t-- key:${key}"); instance.setString(key, value as String); break; case int: instance.setInt(key, value as int); break; case double: instance.setDouble(key, value as double); break; case bool: instance.setBool(key, value as bool); break; }} / / / for stored value / / / -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- - / / / -- -- -- -- -- -- -- -- -- -- he has to write a generic!!!!!!!!!! ---------- /// --------------------------------- static Future<T> getDate<T>(String key) async{ SharedPreferences instance = await SharedPreferences.getInstance(); var t; switch (T) { case String: print("SpUtilgetData:T:${T}\t-- key:${key}"); t = await instance.getString(key); break; case int: t = instance.getInt(key); break; case double: t = instance.getDouble(key); break; case bool: t = instance.getBool(key); break; } return t; */ static setStringList(String key,List<String> value)async{SharedPreferences instance= await  SharedPreferences.getInstance(); instance.setStringList(key, value); } static Future<List<String>> getStringList(String key) async{SharedPreferences instance= await SharedPreferences.getInstance(); return instance.getStringList(key); } / * * * * / delete key corresponding value static remove (String key) async {SharedPreferences instance = await SharedPreferences. GetInstance ();  instance.remove(key); }}Copy the code

Use:

Remaining value:

SpUtil.setData<String>(TEST_KEY, value);
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Values:

SpUtil.getDate<String>(TEST_KEY).then((value) { _mObtainData = value; Print (" ${value}"); });Copy the code

Util class is mainly convenient to use, some code is fixed, but no one can write every day, do not write easy to forget, and write tool class also improve the code reuse rate

Finally, there is an on/off button to tell whether to use the SpUtil utility class:

Here we go directly to the renderings :(shown at the bottom of the full code)

The complete code

SPUtil tools

Chapter 1 :Flutter Future and FutureBuilder Asynchronous Operation (3.3)

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