Question

I program my first Android app and am very new to Android development (as well as Java). I have PreferenceActivity and noticed that when activity is shown and I turn off mobile its onCreate() is called once again. Even more confusing is that static member MyFirstAppActivity.camera is not existing anymore causing exceptions. I can put check for null in there but I wonder why is this happening and whats the best way to avoid it?

public class SettingsActivity extends PreferenceActivity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

     // Root
        addPreferencesFromResource(R.xml.preferences);

        // get list of available resolutions

        Object[] previewSizes = MyFirstAppActivity.camera.getParameters()
                .getSupportedPreviewSizes().toArray();

        // split object properties into two arrays

        String[] ps=new String[previewSizes.length];

        for(int i=0;i<previewSizes.length;i++)
        {
            try
            {
                int width=((Size)previewSizes[i]).width;
                int height=((Size)previewSizes[i]).height;
                ps[i]=width+"x"+height;
            }
            catch(Exception ex)
            {}
        }

        // get list of available resolutions

        Object[] recordingSizes = MyFirstAppActivity.camera.getParameters()
                .getSupportedPictureSizes().toArray();

        // split object properties into two arrays

        String[] rs=new String[recordingSizes.length];

        for(int i=0;i<recordingSizes.length;i++)
        {
            try
            {
                int width=((Size)recordingSizes[i]).width;
                int height=((Size)recordingSizes[i]).height;
                rs[i]=width+"x"+height;
            }
            catch(Exception ex)
            {}
        }

        Preference prefPreviewSizes = getPreferenceManager().findPreference("previewSizes");
        Preference prefRecordingSizes = getPreferenceManager().findPreference("recordingSizes");

        ((ListPreference) prefPreviewSizes).setEntries(ps);
        ((ListPreference) prefRecordingSizes).setEntries(rs);

    }
}

Answer 1

Whenever some sort of state change happens (for example, turning off or rotating the screen) the onCreate method gets called.

I’m pretty sure what you’re supposed to do is override the onSaveInstanceState method and save data to it’s outState Bundle, which then gets passed to onCreate as the savedInstanceState Bundle.

For some more info, check out “Handling Runtime Changes” in the Android developer center.

You might be able to keep your camera from causing exceptions by checking if it exists before creating it, something like

if(MyFirstAppActivity.camera == null)
    MyFirstAppActivity.camera = new Camera(...);

or just create a new instance of it in onCreate