Saving Hashmap of arraylist in Android

Question

I am trying to save hashmap of arraylist. I am using custom class MailMessage which is itself parcelable. How can I save the Hashmaps? I am saving/restoring map as:

<code>
HashMap<String, ArrayList<MailMessage>> emailsMap = new HashMap<String, ArrayList<MailMessage>>();

@Override
    protected void onSaveInstanceState(Bundle outState) {
        outState.putSerializable("emailsMap", emailsMap);
        super.onSaveInstanceState(outState);
    }

    @Override
    protected void onRestoreInstanceState(Bundle state) {
        // TODO Auto-generated method stub
        super.onRestoreInstanceState(state);
        emailsMap = (HashMap<String, ArrayList<MailMessage>>) state.getSerializable("emailsMap");
    }
</code>

But in restore instance state, i am getting empty map. What can be the issue? I am saving restoring in right way?

I always, serialize them to Json and getting them Back with gson, but not sure if it is the absolute right way — A.S., Mar 03 '14 at 13:05
Parcelable does not help you if you use serialize later. I'd recommend you to implement Serializable in `MailMessage`, even if that's not as efficient as parcelable. — FD_, Mar 03 '14 at 13:11

score 0 · Answer 1 · answered Mar 03 '14 at 13:14

you can use shared preference to set and get your hashmap.

 /**
 * This method is used to set shared preferences
 * @param context Application context
 * @param key shared object key
 * @param value shared object value
 */
public static void setPreferences(Context context, String key, Object value) {
    SharedPreferences appSharedPrefs = PreferenceManager
            .getDefaultSharedPreferences(context);
    Editor prefsEditor = appSharedPrefs.edit();
    Gson gson = new Gson();
    String json = gson.toJson(value);
    prefsEditor.putString(key, json);
    prefsEditor.commit();
}

/**
 * This method is used to get shared object
 * @param context Application context
 * @param key shared object key
 * @return return value, for default "" asign.
 */
public static HashMap<String, ArrayList<MailMessage>> getPreferences(Context context, String key,
        Class<HashMap<String, ArrayList<MailMessage>>> clazz) {

    SharedPreferences appSharedPrefs = PreferenceManager
            .getDefaultSharedPreferences(context);

    Gson gson = new Gson();
    String json = appSharedPrefs.getString(key, "");
    if (TextUtils.isEmpty(json)) {
        return null;
    }
    return (HashMap<String, ArrayList<MailMessage>>) gson.fromJson(json, clazz);
}

Make sure when you call getPreference to get hashmap, your key is as same as you had used when you have store your object using setSharedPrefence.

Saving Hashmap of arraylist in Android

1 Answers1