Android ArrayList of custom objects - Save to SharedPreferences - Serializable?
Yes, you can save your composite object in shared preferences. Let's say..
Student mStudentObject = new Student();
SharedPreferences appSharedPrefs = PreferenceManager
.getDefaultSharedPreferences(this.getApplicationContext());
Editor prefsEditor = appSharedPrefs.edit();
Gson gson = new Gson();
String json = gson.toJson(mStudentObject);
prefsEditor.putString("MyObject", json);
prefsEditor.commit();
..and now you can retrieve your object as:
SharedPreferences appSharedPrefs = PreferenceManager
.getDefaultSharedPreferences(this.getApplicationContext());
Gson gson = new Gson();
String json = appSharedPrefs.getString("MyObject", "");
Student mStudentObject = gson.fromJson(json, Student.class);
For more information, click here.
If you want to get back an ArrayList
of any type object e.g. Student
, then use:
Type type = new TypeToken<List<Student>>(){}.getType();
List<Student> students = gson.fromJson(json, type);
Save ArrayList to SharedPreferences
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();
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
How to save List Object to SharedPreferences?
It only possible to use primitive types because preference keep in memory. But what you can use is serialize your types with Gson into json and put string into preferences:
private static SharedPreferences sharedPreferences = context.getSharedPreferences(STORE_FILE_NAME, Context.MODE_PRIVATE);
private static SharedPreferences.Editor editor = sharedPreferences.edit();
public <T> void setList(String key, List<T> list) {
Gson gson = new Gson();
String json = gson.toJson(list);
set(key, json);
}
public static void set(String key, String value) {
editor.putString(key, value);
editor.commit();
}
Extra Shot from below comment by @StevenTB
To Retrive
public List<YourModel> getList(){
List<YourModel> arrayItems;
String serializedObject = sharedPreferences.getString(KEY_PREFS, null);
if (serializedObject != null) {
Gson gson = new Gson();
Type type = new TypeToken<List<YourModel>>(){}.getType();
arrayItems = gson.fromJson(serializedObject, type);
}
}
ArrayList of custom objects not saving to SharedPreferences with GSON
Try to remove AtomicReference
and add item
to list
directly as in
ArrayList<ItmModel> arrayList = new ArrayList<>();
ItmModel itmModel = new ItmModel(item.getText().toString(), attr.getText().toString(),pric.getText().toString(), sise.getText().toString(), image, company);
arrayList.add(itmModel);
Gson gson = new Gson();
Type type = new TypeToken<ArrayList<ItmModel>>() {}.getType();
String list = gson.toJson(arrayList, type);
prefsEditor.putString("Cart", list);
prefsEditor.apply();
Why are you even extending ArrayList
in POJO
, remove and modify part of your POJO
to below
public class ItmModel implements Parcelable, Serializable {
@SuppressWarnings("unused")
public static final Parcelable.Creator<ItmModel> CREATOR = new Parcelable.Creator<ItmModel>() {
@Override
public ItmModel createFromParcel(Parcel in) {
return new ItmModel(in);
}
@Override
public ItmModel[] newArray(int size) {
return new ItmModel[size];
}
};
@Expose
private String name;
@Expose
private String attr;
@Expose
private String size;
@Expose
private String pric;
@Expose
private String imag;
@Expose
private String comp;
//rest of code as it is
}
Save custom object array to Shared Preferences
You can use gson to serialize class objects and store them into SharedPreferences. You can downlaod this jar from here https://code.google.com/p/google-gson/downloads/list
SharedPreferences mPrefs = getPreferences(Context.MODE_PRIVATE);
To Save:
Editor prefsEditor = mPrefs.edit();
Gson gson = new Gson();
String json = gson.toJson(MyObject);
prefsEditor.putString("MyObject", json);
prefsEditor.commit();
To Retreive:
Gson gson = new Gson();
String json = mPrefs.getString("MyObject", "");
MyObject obj = gson.fromJson(json, MyObject.class);
Android. Easy way to save small arrayList of custom objects
There is a library for this kind of stuff with easy solution
compile 'com.google.code.gson:gson:2.4'
So, by importing this you can directly save/retrive you arrylist like this ::
SAVE ::
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(context);
Type listOfBecons = new TypeToken<List<BeaconDevice>>() {}.getType();
String strBecons = new Gson().toJson(SavedBeacons, listOfBecons);
preferences.edit().putString("BECON_LIST", strBecons).apply();
RETRIEVE::
ArrayList<BeaconDevice> mSavedBeaconList = new Gson().fromJson(preferences.getString("BECON_LIST", ""), listOfBecons);
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