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

别忘了实现Serializable:

Class dataBean implements Serializable{
 public String name;
}
ArrayList<dataBean> dataBeanArrayList = new ArrayList();

https://stackoverflow.com/a/7635154/4639974

其他回答

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

在SharedPreferences中使用getStringSet和putStringSet非常简单,但在我的情况下,我必须在向Set中添加任何东西之前复制Set对象。否则,Set将不会被保存,如果我的应用程序是强制关闭。可能是因为下面API中的注释。(如果应用程序被返回按钮关闭,则保存)。

注意,您不能修改此调用返回的set实例。如果这样做,则无法保证存储数据的一致性,也无法保证修改实例的能力。 http://developer.android.com/reference/android/content/SharedPreferences.html#getStringSet

SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getActivity());
SharedPreferences.Editor editor = prefs.edit();

Set<String> outSet = prefs.getStringSet("key", new HashSet<String>());
Set<String> workingSet = new HashSet<String>(outSet);
workingSet.add("Another String");

editor.putStringSet("key", workingSet);
editor.commit();

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();
public class VcareSharedPreference {
  private static VcareSharedPreference sharePref = new VcareSharedPreference(); 
  private static SharedPreferences sharedPreferences; 
  private static SharedPreferences.Editor editor;
  private VcareSharedPreference() {
 } 
public static VcareSharedPreference getInstance(Context context) {
    if (sharedPreferences == null) {
        sharedPreferences = context.getSharedPreferences(context.getPackageName(), Activity.MODE_PRIVATE);
        editor = sharedPreferences.edit();
    }
    return sharePref;
 }
public void save(String KEY, String text) {
    editor.putString(KEY, text);
    editor.commit();
}
 public String getValue(String PREFKEY) {
    String text;

    //settings = PreferenceManager.getDefaultSharedPreferences(context);
    text = sharedPreferences.getString(PREFKEY, null);
    return text;
}
public void removeValue(String KEY) {
    editor.remove(KEY);
    editor.commit();
}

public void clearAll() {
    editor.clear();
    editor.commit();
}
public void saveArrayList(String key, ArrayList<ModelWelcome> modelCourses) {
    Gson gson = new Gson();
    String json = gson.toJson(modelCourses);
    editor.putString(key, json);
    editor.apply();
}

public ArrayList<ModelWelcome> getArray(String key) {

    Gson gson = new Gson();
    String json = sharedPreferences.getString(key, null);
    Type type = new TypeToken<ArrayList<ModelWelcome>>() {
    }.getType();
 return gson.fromJson(json, type);}}

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