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

使用Kotlin和GSON:

fun <T> SharedPreferences.writeList(gson: Gson, key: String, data: List<T>) {
    val json = gson.toJson(data)
    edit { putString(key, json) }
}

inline fun <reified T> SharedPreferences.readList(gson: Gson, key: String): List<T> {
    val json = getString(key, "[]") ?: "[]"
    val type = object : TypeToken<List<T>>() {}.type
    
    return try {
        gson.fromJson(json, type)
    } catch(e: JsonSyntaxException) {
        emptyList()
    }
}

其他回答

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。

您可以将其转换为Map Object来存储它,然后在检索SharedPreferences时将值更改回ArrayList。

我已经阅读了上面所有的答案。这都是正确的,但我找到了一个更简单的解决方案如下:

Saving String List in shared-preference>> public static void setSharedPreferenceStringList(Context pContext, String pKey, List<String> pData) { SharedPreferences.Editor editor = pContext.getSharedPreferences(Constants.APP_PREFS, Activity.MODE_PRIVATE).edit(); editor.putInt(pKey + "size", pData.size()); editor.commit(); for (int i = 0; i < pData.size(); i++) { SharedPreferences.Editor editor1 = pContext.getSharedPreferences(Constants.APP_PREFS, Activity.MODE_PRIVATE).edit(); editor1.putString(pKey + i, (pData.get(i))); editor1.commit(); } } and for getting String List from Shared-preference>> public static List<String> getSharedPreferenceStringList(Context pContext, String pKey) { int size = pContext.getSharedPreferences(Constants.APP_PREFS, Activity.MODE_PRIVATE).getInt(pKey + "size", 0); List<String> list = new ArrayList<>(); for (int i = 0; i < size; i++) { list.add(pContext.getSharedPreferences(Constants.APP_PREFS, Activity.MODE_PRIVATE).getString(pKey + i, "")); } return list; }

这里的常数。APP_PREFS是要打开的文件的名称;不能包含路径分隔符。

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;
}

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());