Question

I have an ArrayList of Persons (ArrayList<Person>), I want to store that ArrayList in a persistent data type. SharedPreferences are a solution BUT it’s just manipulating String, int, float`… variables. Do you have some ideas?
Thank you very much.

Answer 1

Much simpler is to use java Serialisation.

You just need an Persons class:

public class Persons {

  ArrayList<Person> personList;
}

Then simply use

// init Persons
Persons person = new Persons();
// add some
persons.personList.add(new Person());

// write out
ObjectOutpuStream oos = new ObjectOutputStream(new BufferOutputStream(new FileOutputStream("personsDB.ser")));

oos.writeObject(persons);
oos.close();

read back with

ObjectInputStream ois = new ObjectInputStream(new BufferedInpuStream(new FileInpuStream("personsDB.ser")));
persons = (Persons) ois.readObject();
ois.close();
// ready! Java does that all for you; since Persons is one object which contains something

The disadvantage is when battery power is lost during writing. Some people write to a temporary file first, delete the old and rename to the correct file name.

For high performance (much less space, much faster)
You could use DataOutputStream, but then you have to write all fields yourself (but this is simple too)