How to save custom ArrayList on Android screen rotate?

I have an ArrayList with custom objects that I would like to be able to save and restore on a screen rotate.

I know that this can be done with onSaveInstanceState and onRestoreInstanceState if I were to make the ArrayList its own class, which implements either Parcelable or Serializable... But is there a way to do this without creating another class?

You do not need to create a new class to pass an ArrayList of your custom objects. You should simply implement the Parcelable class for your object and use Bundle#putParcelableArrayList() in onSaveInstanceState() and onRestoreInstanceState(). This method will store an ArrayList of Parcelables by itself.

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Because the subject of Parcelables (and Serializables and Bundles) sometimes makes my head hurt, here is a basic example of an ArrayList containing custom Parcelable objects stored in a Bundle. (This is cut & paste runnable, no layout necessary.)

Implementing Parcelable

public class MyObject implements Parcelable {
	String color;
	String number;

	public MyObject(String number, String color) {
		this.color = color;
		this.number = number;
	}
	
	private MyObject(Parcel in) {
		color = in.readString();
		number = in.readString();
	}
	
	public int describeContents() {
		return 0;
	}

	@Override
	public String toString() {
		return number + ": " + color;
	}

	public void writeToParcel(Parcel out, int flags) {
		out.writeString(color);
		out.writeString(number);
	}

	public static final Parcelable.Creator<MyObject> CREATOR = new Parcelable.Creator<MyObject>() {
		public MyObject createFromParcel(Parcel in) {
			return new MyObject(in);
		}

		public MyObject[] newArray(int size) {
			return new MyObject[size];
		}
	};
}

Save / Restore States

public class Example extends ListActivity {
	ArrayList<MyObject> list;
	
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		
		if(savedInstanceState == null || !savedInstanceState.containsKey("key")) {
			String[] colors = {"black", "red", "orange", "cyan", "green", "yellow", "blue", "purple", "magenta", "white"};
			String[] numbers = {"one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten"};
			
			list = new ArrayList<MyObject>();
			for(int i = 0; i < numbers.length; i++) 
				list.add(new MyObject(numbers[i], colors[i]));
		}
		else {
			list = savedInstanceState.getParcelableArrayList("key");
		}
		
		setListAdapter(new ArrayAdapter<MyObject>(this, android.R.layout.simple_list_item_1, list));
	}
	
	@Override
	protected void onSaveInstanceState(Bundle outState) {
		outState.putParcelableArrayList("key", list);
		super.onSaveInstanceState(outState);
	}
}

You can use onRetainNonConfigurationInstance(). It allows you to save any object before an configuration change, and restore it after with getLastNonConfigurationInstanceState().

Inside the activity:

    @Override
    public Object onRetainNonConfigurationInstance() {
        return myArrayList;
    }

Inside onCreate():

    try{
        ArrayList myArrayList = (ArrayList)getLastNonConfigurationInstance();
    } catch(NullPointerException e) {}

Handling Runtime Changes: http://developer.android.com/guide/topics/resources/runtime-changes.html Documentation: http://developer.android.com/reference/android/app/Activity.html#onRetainNonConfigurationInstance%28%29

public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    ArrayList<Integer> id=new ArrayList<>();
    ArrayList<String> title=new ArrayList<>();
    for(int i=0;i<arr.size();i++){
        id.add(arr.get(i).id);
        title.add(arr.get(i).title);
    }
    outState.putIntegerArrayList("id",id);
    outState.putStringArrayList("title",title);
}

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());
     Editor prefsEditor = appSharedPrefs.edit();
     Gson gson = new Gson();
     String json = appSharedPrefs.getString("MyObject", "");
     Student mStudentObject = gson.fromJson(json, Student.class);