Question

I have a question about rotating the Android device. My code logs a static and non-static attribute in onCreate(…).

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;

public class MainActivity extends Activity {
    static int sn;
    int n;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        sn++;
        n++;

        Log.i("onCreate", String.format("sn=%d n=%d", sn, n));
    }
}

The screen orientation is portrait. When I first ran the code, I got:

onCreate(): sn=1 n=1

After I rotated the screen to landscape, I got:

onCreate(): sn=2 n=1

After I rotated the screen again to portrait, I got:

onCreate(): sn=3 n=1
onCreate(): sn=4 n=1

My questions are:

1. How can I prevent onCreate(…) to be called twice when the device is rotated back to portrait?
2. How can I save the value of non-static variable when the device is rotated?

Answer 1

Whenever the screen orientation is changed, that Activity is destroyed and a new activity starts by onCreate() method.
so every time you rotate the screen that activity will be destroyed and a new activity starts by onCreate() method.
You can save Non Static member by overriding onSaveInstanceState(Bundle b) method.
Android calls this method whenever the screen is rotated, and that given bundle b would be passed to oncreate(Bundle b) from which you can extract your non static member.