Save an arraylist of Strings to shared preferences

Question

What is the best way to save an ArrayList of strings to SharedPreferences in API level 8? The only way i can think of now is to save all of the strings into one string separated by commas and save it that way. But I don't know if there is a maximum size for strings.

Is there a better way to do this?

Answer 1

If you can guarantee your Strings in ArrayList don't contain comma, you can simply use

List<String> list = new ArrayList<String>();
...
editor.putString(PREF_KEY_STRINGS, TextUtils.join(",", list));

and to read the list

String serialized = prefs.getString(PREF_KEY_STRINGS, null);
List<String> list = Arrays.asList(TextUtils.split(serialized, ","));

You are limited by the memory of the device. It's good practice to use background thread to read/write shared preferences.

Answer 2

I suggest you to save the arraylist as Internal Storage File in Android. For example for a arraylist named text_lines:

Internal storage File IO (Writing) :

try {
   //Modes: MODE_PRIVATE, MODE_WORLD_READABLE, MODE_WORLD_WRITABLE
   FileOutputStream output = openFileOutput("lines.txt",MODE_WORLD_READABLE);
   DataOutputStream dout = new DataOutputStream(output);
   dout.writeInt(text_lines.size()); // Save line count
   for(String line : text_lines) // Save lines
      dout.writeUTF(line);
   dout.flush(); // Flush stream ...
   dout.close(); // ... and close.
}
catch (IOException exc) { exc.printStackTrace(); }

Interal storage File IO (Reading) :

FileInputStream input = openFileInput("lines.txt"); // Open input stream
DataInputStream din = new DataInputStream(input);
int sz = din.readInt(); // Read line count
for (int i=0;i<sz;i++) { // Read lines
   String line = din.readUTF();
   text_lines.add(line);
}
din.close();

Answer 3

There is a method, putStringSet(), in SharedPreferences.Editor, which you can take advantage of if your strings are a Set. (That is, no duplicates).