Android app resets on orientation change, best way to handle?

Question

So I am making a basic chess app to play around with some various elements of android programming and so far I am learning a lot, but this time I am lost.

When the orientation of the emulator changes the activity gets reset. Based on my research the same thing will happen anytime the application is paused/interrupted, ie. keyboard change, phone call, hitting the home key etc.

Obviously, it is not viable to have a chess game constantly reset, so once again I find myself needing to learn how to fix this problem.

My research brings up a few main things, overriding the onPaused method in my Activity, listening for Orientation, Keyboard changes in my manifest (via android:configChanges), using Parcelables, or Serialization.

I have looked up a lot of sample code using Pacelables, but to be honest it is too confusing. Maybe coming back tomorrow with fresh eyes will be beneficial, but right now the more I look at Parcelables the less sense it makes.

My application utilizes a Board object, which has 64 Cell Objects(in an 8x8 2D array), and each cell has a Piece Object, either an actual piece or null if the space is empty. Assuming that I use either Parcelable or Serialization I am assuming that I would have to Parcelize or Serialize each class, Board, Cell, and Piece.

First and foremost, is Parcelable or Serialization even the right thing to be looking at for this problem? If so is either Parcelable or Serializable preferred for this? And am I correct in assuming that each of the three objects would have to be Parceled/Serialized? Finally, does anybody have a link to a simple to understand Parcelable tutorial? Anything to help me understand, and stop further headaches down the road when my application expands even further.

Any help would be appreciated.

Answer 1

Androids default way of handling the events is to recreate the activity. Basically you handle one process correctly and everything works, no need to worry about handling those things manually.

The Application Fundamentals has a complete overview of the activity life cycle, but in short you want to save your activity state in the onSaveInstanceState() method and use the Bundle you get in the onCreate(Bundle savedInstanceState) to restore your application state.

If you want to store your classes in the Bundle your best bet is to implement the Parcelable interface. Then to save your state you do:

protected void onSaveInstanceState(Bundle outState)
{
  super.onSaveInstanceState(outState);
  outState.putParcelable("yourObject", mYourObject);
}

and in the onCreate method you simply do:

if (savedInstanceState != null)
  mYourObject = savedInstanceState.getParcelable("yourObject");

Of course you could just convert your objects into normal array representations that the Bundle can already contain and just skip implementing the Parcelable interface. Basically add a method toArray() to your object and a static method fromArray(). Well, play around and see which suits you better.

Answer 2

Override onRetainNonConfigurationInstance in your Activity class.

In this method you must return an object, just bundle up your game's state in a single state object and return it in this method. Make sure this is only a state object, by that i mean it should have no handles to an activity, view, etc. contained within it or you'll get memory leaking.

In your onCreate method call getLastNonConfigurationInstance to get the object back.

You don't have to worry about the implementation details (the serialization) android takes care of that.

If you haven't already make sure you've set your Launch Mode in the manifest to either singleTask or singleInstance depending on which fits your needs better. By default if someone hits home and then comes back to your application it launches a new copy of the activity, if not handled or configured for single instance you'll get multiple copies of your game activity running.

Answer 3

Or stick this line in your OnCreate so it doesn't roate. Problem solved.

setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);

Answer 4

in your manifest in the <Activity> tag, you can add android:configChanges="orientation|keyboardHidden", this will stop the activity from reloading and call onConfigurationChanged() instead when the orientation is changed or the keyboard is hidden.

If you need to make adjustments when either of these events happen, you can override onConfigurationChanged() in your activity, if not all you have to do is add the property to the manifest.

Answer 5

When you save the board state, make an int[64] and at each position store the corresponding piece. So 0=empty, 1=white pawn, 2=white knight, etc...

When you load the board state, iterate through the array and create the appropriate piece objects at the appropriate locations.

You can convert the int[64] to a string to store in SharedPreferences, or use it with a Parcelable or whatever. Only store the minimum data you need.

Answer 6

I want to lock the orientation of the screen to portrait when hard keyboard is not open and want the orientation of the screen to landscape when hard keyboard is open. The only difference between normal behavior and in mine that I don't want the orientation to be changed when screen is just rotated and hard keyboard is not open. Please suggest.