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

请在kotlin中使用这两种方法将数据存储在ArrayList中

fun setDataInArrayList(list: ArrayList<ShopReisterRequest>, key: String, context: Context) {
    val prefs = PreferenceManager.getDefaultSharedPreferences(context)
    val editor = prefs.edit()
    val gson = Gson()
    val json = gson.toJson(list)
    editor.putString(key, json)
    editor.apply()   
}

fun getDataInArrayList(key: String, context: Context): ArrayList<ShopReisterRequest> {
    val prefs = PreferenceManager.getDefaultSharedPreferences(context)
    val gson = Gson()
    val json = prefs.getString(key, null)
    val type = object : TypeToken<ArrayList<ShopReisterRequest>>() {

    }.type
    return gson.fromJson<ArrayList<ShopReisterRequest>>(json, type)
}  

其他回答

该方法用于存储/保存数组列表:-

 public static void saveSharedPreferencesLogList(Context context, List<String> collageList) {
            SharedPreferences mPrefs = context.getSharedPreferences("PhotoCollage", context.MODE_PRIVATE);
            SharedPreferences.Editor prefsEditor = mPrefs.edit();
            Gson gson = new Gson();
            String json = gson.toJson(collageList);
            prefsEditor.putString("myJson", json);
            prefsEditor.commit();
        }

该方法用于检索数组列表:-

public static List<String> loadSharedPreferencesLogList(Context context) {
        List<String> savedCollage = new ArrayList<String>();
        SharedPreferences mPrefs = context.getSharedPreferences("PhotoCollage", context.MODE_PRIVATE);
        Gson gson = new Gson();
        String json = mPrefs.getString("myJson", "");
        if (json.isEmpty()) {
            savedCollage = new ArrayList<String>();
        } else {
            Type type = new TypeToken<List<String>>() {
            }.getType();
            savedCollage = gson.fromJson(json, type);
        }

        return savedCollage;
    }

您可以将其转换为JSON字符串,并将字符串存储在SharedPreferences中。

在API 11之后,SharedPreferences Editor接受set。您可以将List转换为HashSet或类似的东西,并像这样存储它。当你把它读回来时,把它转换成一个数组列表,如果需要的话对它排序,你就可以开始了。

//Retrieve the values
Set<String> set = myScores.getStringSet("key", null);

//Set the values
Set<String> set = new HashSet<String>();
set.addAll(listOfExistingScores);
scoreEditor.putStringSet("key", set);
scoreEditor.commit();

你也可以序列化你的数组列表,然后将它保存/读取到SharedPreferences。解决方案如下:

编辑: 下面是将ArrayList作为一个序列化对象保存到SharedPreferences的解决方案,然后从SharedPreferences中读取它。

因为API只支持在SharedPreferences中存储和检索字符串(在API 11之后,它更简单),我们必须序列化和反序列化ArrayList对象,它将任务列表变成一个字符串。

在TaskManagerApplication类的addTask()方法中,我们必须获取共享首选项的实例,然后使用putString()方法存储序列化的ArrayList:

public void addTask(Task t) {
  if (null == currentTasks) {
    currentTasks = new ArrayList<task>();
  }
  currentTasks.add(t);
 
  // save the task list to preference
  SharedPreferences prefs = getSharedPreferences(SHARED_PREFS_FILE, Context.MODE_PRIVATE);
  Editor editor = prefs.edit();
  try {
    editor.putString(TASKS, ObjectSerializer.serialize(currentTasks));
  } catch (IOException e) {
    e.printStackTrace();
  }
  editor.commit();
}

类似地,我们必须从onCreate()方法中的首选项中检索任务列表:

public void onCreate() {
  super.onCreate();
  if (null == currentTasks) {
    currentTasks = new ArrayList<task>();
  }
 
  // load tasks from preference
  SharedPreferences prefs = getSharedPreferences(SHARED_PREFS_FILE, Context.MODE_PRIVATE);
 
  try {
    currentTasks = (ArrayList<task>) ObjectSerializer.deserialize(prefs.getString(TASKS, ObjectSerializer.serialize(new ArrayList<task>())));
  } catch (IOException e) {
    e.printStackTrace();
  } catch (ClassNotFoundException e) {
    e.printStackTrace();
  }
}

您可以从Apache Pig项目ObjectSerializer.java中获得ObjectSerializer类

您可以使用序列化或Gson库将列表转换为字符串,反之亦然,然后将字符串保存在首选项中。

使用谷歌的Gson库:

//Converting list to string
new Gson().toJson(list);

//Converting string to list
new Gson().fromJson(listString, CustomObjectsList.class);

使用Java序列化:

//Converting list to string
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(bos);
oos.writeObject(list);
oos.flush();
String string = Base64.encodeToString(bos.toByteArray(), Base64.DEFAULT);
oos.close();
bos.close();
return string;

//Converting string to list
byte[] bytesArray = Base64.decode(familiarVisitsString, Base64.DEFAULT);
ByteArrayInputStream bis = new ByteArrayInputStream(bytesArray);
ObjectInputStream ois = new ObjectInputStream(bis);
Object clone = ois.readObject();
ois.close();
bis.close();
return (CustomObjectsList) clone;

我的utils类保存列表到SharedPreferences

public class SharedPrefApi {
    private SharedPreferences sharedPreferences;
    private Gson gson;

    public SharedPrefApi(Context context, Gson gson) {
        this.sharedPreferences = context.getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE);
        this.gson = gson;
    } 

    ...

    public <T> void putList(String key, List<T> list) {
        SharedPreferences.Editor editor = sharedPreferences.edit();
        editor.putString(key, gson.toJson(list));
        editor.apply();
    }

    public <T> List<T> getList(String key, Class<T> clazz) {
        Type typeOfT = TypeToken.getParameterized(List.class, clazz).getType();
        return gson.fromJson(getString(key, null), typeOfT);
    }
}

使用

// for save
sharedPrefApi.putList(SharedPrefApi.Key.USER_LIST, userList);

// for retrieve
List<User> userList = sharedPrefApi.getList(SharedPrefApi.Key.USER_LIST, User.class);

. 我的utils的完整代码//检查使用实例的活动代码