Question

我找到了这个，我正在尝试重新创建它。

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

void main() {
  runApp(new MaterialApp(
    home: new Scaffold(
      body: new Center(
        child: new RaisedButton(
          onPressed: _save,
          child: new Text('Save my list of int'),
        ),
      ),
    ),
  ));
}

_save() async {

  List<int> myListOfIntegers = [1,2,3,4];
  List<String> myListOfStrings=  myListOfIntegers.map((i)=>i.toString()).toList();

  SharedPreferences prefs = await SharedPreferences.getInstance();
  List<String> myList = (prefs.getStringList('mylist') ?? List<String>()) ;
  List<int> myOriginaList = myList.map((i)=> int.parse(i)).toList();
  print('Your list  $myOriginaList');
  await prefs.setStringList('mylist', myListOfStrings);
}

我在导入为选项的外部文件中有一个名为timerValuesList的列表。现在我不明白SharedPreferences pref = ...之后的行，为什么还有另一个字符串列表？那是为了在不存在的情况下创建列表吗？这是我的文件。我也会负担。

现在我已经尝试了。我注意到这一切都很好，但是当我在某些小部件中使用值时，例如timerValuesList [0]，它显示的是30.0，而不是我在其他函数中修改的值，然后将其保存到sharedpref。但是，如果我随后编辑例如+1的值，则它不是从显示的30.0开始，而是从我上次编辑并更新的值开始。因此，这是正确的值，但是直到我更新屏幕后才向我显示。你知道为什么吗？该问题仅在我首次启动该应用程序时出现，之后再没问题，这就是为什么我虽然将loadSharedPreferences放在initState中但仍然出现。

List<double> timersValuesList = [30.0, 60.0, 90.0, 120.0, 150.0, 180.0];

void saveSharedPreferences() async {
  // from List of double to a List of String
  List<String> convertedTimerValues = timersValuesList.map((i) => i.toString()).toList();
  // getting the instance of sharedPreferences as Object prefs
  SharedPreferences prefs = await SharedPreferences.getInstance();
  // taking my List as key of "mylist", if it doesn't exist create empty List, this is List of String
  List<String> myList = (prefs.getStringList('mylist') ?? List<String>());
  //saving the List of String as key"mylist"
  await prefs.setStringList('mylist', convertedTimerValues);
}

void loadSharedPreferences() async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  List<String> myList = (prefs.getStringList('mylist') ?? List<String>());
  List<double> myOriginalList = myList.map((i)=> double.parse(i)).toList();
  timersValuesList = myOriginalList;
//    print('Your list  $myOriginalList');
}

Answer 1

不能100％确定您不了解的内容，

SharedPreferences prefs = await SharedPreferences.getInstance();

很明显，上面是在获取SharedPreferences实例。

List<String> myList = (prefs.getStringList('mylist') ?? List<String>());

上面说的是获取myList和“ ??”如果为null，则创建一个空列表。

Answer 2

在Public Function StringFixLeft(AStr As Variant, SLen As Integer) As String If (IsNull(AStr)) Then AStr = "" If (Len(AStr) = 0) Then AStr = " " StringFixLeft = UCase(Format(Left(AStr, SLen), "!" & String(SLen, "@"))) End Function Public Function StringFixRight(AStr As Variant, SLen As Integer) As String If (IsNull(AStr)) Then AStr = "" If (Len(AStr) = 0) Then AStr = " " StringFixRight = UCase(Format(Left(AStr, SLen), String(SLen, "@"))) End Function // Here is what I wrote in PHP. function StringFixRight($AStr, $SLen) { if ($AStr === NULL) {$AStr = "";} if (strlen($AStr) = 0) {$AStr = "";} $StringFixRight = strtoupper(substr($AStr,0,$SLen)); return $StringFixRight; } function StringFixLeft($AStr, $SLen) { if ($AStr === NULL) {$AStr = "";} if (strlen($AStr) = 0) {$AStr = "";} $StringFixRight = strtoupper(substr($AStr,0,$SLen)); return $StringFixRight; } // basically the line I cannot figure out is the last line in the function StringFixLeft = UCase(Format(Left(AStr, SLen), "!" & String(SLen, "@"))) StringFixRight = UCase(Format(Left(AStr, SLen), String(SLen, "@"))) // need to convert these to PHP中，您需要输入SharedPreferences作为密钥来保存您的价值。获取实例后

String

下一行使用键SharedPreferences prefs = await SharedPreferences.getInstance();检索列表（它是String的列表）。

'mylist'

在下一行中，代码通过解析List<String> myList = (prefs.getStringList('mylist') ?? List<String>());

中的字符串将其映射到整数列表

myList

您可以

setBool
setInt
setDouble
setString
setStringList

如何保存：

List<int> myOriginaList = myList.map((i)=> int.parse(i)).toList();

您会发现其他功能来保存其他类型的价值。

要检索：

SharedPreferences prefs = await SharedPreferences.getInstance();
await prefs.setStringList('your_string_list_key', yourStringList);

共享首选项学习。如何保存和加载

2 个答案: