机遇屋-Flutter shared_preferences数据存储工具类库

Flutter shared_preferences数据存储工具类库

作者：ych

### 介绍
[pub库](https://pub.dev/packages/shared_preferences "pub库")
在原生的andriod 和iOS 里面都会有数据缓存的api  Android 端用的是 Sharedpreferences  来实现对于轻量级数据的缓存 , IOS端 通常使用NSUserDefaults 来实现轻量级数据的缓存 但是在flutter 有基于Android  iOS  做支持的三方插件库  shared_preferences

#### 基本用法
存储基本数据类型：
int 类型
```
  onPressed: ()async{
                SharedPreferences prefs = await SharedPreferences.getInstance();
                int counter =  1;
                await prefs.setInt('counter', counter);
              },
```
String类型
```
  onPressed: ()async{
                SharedPreferences prefs = await SharedPreferences.getInstance();
                String  counter =  "1";
                await prefs.setString('counter', counter);
              },
```
bool类型
```
  onPressed: ()async{
                SharedPreferences prefs = await SharedPreferences.getInstance();
                bool counter =false;
                await prefs.setBool('counter', counter);
              },
```
double类型
```
  onPressed: ()async{
                SharedPreferences prefs = await SharedPreferences.getInstance();
                double counter =0.01;
                await prefs.setDouble('counter', counter);
              },
```
listdata类型
```
   onPressed: ()async{
                SharedPreferences prefs = await SharedPreferences.getInstance();
                List<String>counter=["1","2"];
                await prefs.setStringList('counter', counter);
              },
```
取值基本用法
```
 onPressed: ()async{
                SharedPreferences prefs = await SharedPreferences.getInstance();
                 int  counterint =prefs.getInt("counter");
                 String  counter =prefs.getString("counter");
                 bool  counterbool =prefs.getBool("counter");
                double  counterdouble =prefs.getDouble("counter");
                List  counterlist =prefs.getStringList("counter");
              },
```
删除指定数据
其中key就是你存贮的名称，value就是你存储的值
```
 SharedPreferences prefs = await SharedPreferences.getInstance();
  prefs.remove(key); //删除指定键
```
清空整个缓存
```
 SharedPreferences prefs = await SharedPreferences.getInstance();
 prefs.clear();//清空键值对
```
#### 封装
common
```
import 'package:flutter/cupertino.dart';
import 'package:shared_preferences/shared_preferences.dart';

class Common {
  ///存数据
  static Object savePreference(String key , Object value) async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    if(value is  int ){
      await prefs.setInt(key, value);
    }else if(value is double){
      await prefs.setDouble(key, value);
    }else if(value is bool){
      await prefs.setBool(key, value);
    }else if(value is String){
      await prefs.setString(key, value);
    }else if(value is List){
      await prefs.setStringList(key, value.cast<String>);
    }  else {
      throw new Exception("不能得到这种类型");
    }
  }
  ///取数据
  static Future  getPreference(String key ,Object defaultValue) async{
    SharedPreferences prefs = await SharedPreferences.getInstance();
    if(defaultValue is  int) {
      return prefs.getInt(key);
    }
    else if(defaultValue is  double) {
      return prefs.getDouble(key);
    }
    else if(defaultValue is bool) {
      return prefs.getBool(key);
    }
    else if(defaultValue is String) {
      return prefs.getString(key);
    }
    else if(defaultValue is List) {
      return prefs.getStringList(key);
    }
    else {
      throw new Exception("不能得到这种类型");
    }
  }
   /// 删除指定数据
  static void    remove(String key)async{
    SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.remove(key); //删除指定键
  }
  ///清空整个缓存
  static void    clear()async{
    SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.clear(); ////清空缓存
  }
}
```
#### 工具类具体调用
存储数据：
```
  onPressed: (){
                String counter  = "1";
                Common.savePreference("counter", counter);
              },
            ),
```
取值
直接调用并赋值给定义的变量
```
 onPressed: ()async{
      String  counter = await (Common.getPreference("counter", "1")) as String ;
                 print("counter  -- > "+counter);
     },
```
通过then方式调用
```
 onPressed: ()async{
                 Common.getPreference("counter", "1").then((value){
                   print("value   --->"  +value);
                 });
              },
```
删除指定key的缓存数据调用：
```
   Common.remove("counter");
```
清空整个SharedPreferences缓存：
```
   Common.clear();
```

### 更多
[Flutter shared_preferences 各种基础用法和特别技巧](https://juejin.cn/post/6893369848101863437 "Flutter shared_preferences 各种基础用法和特别技巧")

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