I have an ArrayList with custom objects. Each custom object contains a variety of strings and numbers. I need the array to stick around even if the user leaves the activity and then wants to come back at a later time, however I don't need the array available after the application has been closed completely. I save a lot of other objects this way by using the SharedPreferences but I can't figure out how to save my entire array this way. Is this possible? Maybe SharedPreferences isn't the way to go about this? Is there a simpler method?


当前回答

你可以使用Gson库保存字符串和自定义数组列表。

首先你需要创建一个函数来保存数组列表到SharedPreferences。

public void saveListInLocal(ArrayList<String> list, String key) {

        SharedPreferences prefs = getSharedPreferences("AppName", Context.MODE_PRIVATE);
        SharedPreferences.Editor editor = prefs.edit();
        Gson gson = new Gson();
        String json = gson.toJson(list);
        editor.putString(key, json);
        editor.apply();     // This line is IMPORTANT !!!

    }

你需要创建一个函数来从SharedPreferences获取数组列表。

public ArrayList<String> getListFromLocal(String key)
{
    SharedPreferences prefs = getSharedPreferences("AppName", Context.MODE_PRIVATE);
    Gson gson = new Gson();
    String json = prefs.getString(key, null);
    Type type = new TypeToken<ArrayList<String>>() {}.getType();
    return gson.fromJson(json, type);

}

如何调用保存和检索数组列表函数。

ArrayList<String> listSave=new ArrayList<>();
listSave.add("test1"));
listSave.add("test2"));
saveListInLocal(listSave,"key");
Log.e("saveArrayList:","Save ArrayList success");
ArrayList<String> listGet=new ArrayList<>();
listGet=getListFromLocal("key");
Log.e("getArrayList:","Get ArrayList size"+listGet.size());

不要忘记在你的应用级别build.gradle中添加gson库。

实现“com.google.code.gson: gson: 2.8.2”

其他回答

最好的方法是使用GSON转换为JSOn字符串并保存此字符串到SharedPreference。 我还使用这种方式缓存响应。

正如@nirav所说,最好的解决方案是使用Gson实用工具类将其作为json文本存储在sharedpreferences中。下面是示例代码:

//Retrieve the values
Gson gson = new Gson();
String jsonText = Prefs.getString("key", null);
String[] text = gson.fromJson(jsonText, String[].class);  //EDIT: gso to gson


//Set the values
Gson gson = new Gson();
List<String> textList = new ArrayList<String>(data);
String jsonText = gson.toJson(textList);
prefsEditor.putString("key", jsonText);
prefsEditor.apply();

Android sharedpreferences允许您将基本类型(Boolean, Float, Int, Long, String和StringSet,自API11以来可用)作为xml文件保存在内存中。

任何解决方案的关键思想都是将数据转换为这些基本类型之一。

我个人喜欢将my list转换为json格式,然后将其保存为SharedPreferences值中的字符串。

为了使用我的解决方案,你必须添加谷歌gsonlib。

在gradle中只需添加以下依赖项(请使用谷歌的最新版本):

compile 'com.google.code.gson:gson:2.6.2'

保存数据(HttpParam是你的对象):

List<HttpParam> httpParamList = "**get your list**"
String httpParamJSONList = new Gson().toJson(httpParamList);

SharedPreferences prefs = getSharedPreferences(**"your_prefes_key"**, Context.MODE_PRIVATE);
SharedPreferences.Editor editor = prefs.edit();
editor.putString(**"your_prefes_key"**, httpParamJSONList);

editor.apply();

检索数据(HttpParam是你的对象):

SharedPreferences prefs = getSharedPreferences(**"your_prefes_key"**, Context.MODE_PRIVATE);
String httpParamJSONList = prefs.getString(**"your_prefes_key"**, ""); 

List<HttpParam> httpParamList =  
new Gson().fromJson(httpParamJSONList, new TypeToken<List<HttpParam>>() {
            }.getType());

为什么不把数组列表放在应用程序类上呢?它只有在应用被杀死时才会被销毁,所以,只要应用可用,它就会一直存在。

public static void WriteSharePrefrence1(Context context, String key, 
ArrayList<HashMap<String, String>> value)
{
    final SharedPreferences preferences = 
    PreferenceManager.getDefaultSharedPreferences(context);
    SharedPreferences.Editor editor = preferences.edit();
    Gson gson = new Gson();
    String json = gson.toJson(value);
    editor.putString(key, json);
    editor.commit();
}
public static ArrayList<HashMap<String, String>> ReadSharePrefrence1(Context context, 
 String key)
{
    String data;
    Gson gson = new Gson();
    ArrayList<HashMap<String, String>> items = new ArrayList<>();
    final SharedPreferences preferences = 
    PreferenceManager.getDefaultSharedPreferences(context);
    final SharedPreferences.Editor editor = preferences.edit();
    data = preferences.getString(key, "");

    Type type = new TypeToken<ArrayList<HashMap<String, String>>>() {}.getType();
    items = gson.fromJson(data, type);

    return items;
}