Save ArrayList to SharedPreferences

Question

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?

Answer 1

After API 11 the SharedPreferences Editor accepts Sets. You could convert your List into a HashSet or something similar and store it like that. When you read it back, convert it into an ArrayList, sort it if needed and you're good to go.

//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(); 

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You can also serialize your ArrayList and then save/read it to/from SharedPreferences. Below is the solution:

EDIT:
Ok, below is the solution to save ArrayList as a serialized object to SharedPreferences and then read it from SharedPreferences.

Because API supports only storing and retrieving of strings to/from SharedPreferences (after API 11, it's simpler), we have to serialize and de-serialize the ArrayList object which has the list of tasks into a string.

In the addTask() method of the TaskManagerApplication class, we have to get the instance of the shared preference and then store the serialized ArrayList using the putString() method:

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(); } 

Similarly we have to retrieve the list of tasks from the preference in the onCreate() method:

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();   } } 

You can get the ObjectSerializer class from the Apache Pig project ObjectSerializer.java

Answer 2

Using this object --> TinyDB--Android-Shared-Preferences-Turbo its very simple.

TinyDB tinydb = new TinyDB(context); 

to put

tinydb.putList("MyUsers", mUsersArray); 

to get

tinydb.getList("MyUsers"); 

UPDATE

Some useful examples and troubleshooting might be found here: Android Shared Preference TinyDB putListObject frunction