方向更改时处理SQLiteOpenHelper

Question

The apps I try to create is a ViewPager then consist of Fragments .

Each Fragment has different data, because the got it from Database .

I send the Database class from Fragment Activity to Fragment inside the FragmentStatePagerAdapter .

Here is the code :

private class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter {
    public ScreenSlidePagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        return PageFragment.create(position, student, getApplicationContext(), mDbStudent);
    }

    @Override
    public int getCount() {
        return NUM_PAGES;
    }

}

mDbStudent is the Database class.

I open my mDbStudent at onCreate

And I close my mDbStudent when onDestroy

The problem I have is when The orientation changes, the mDbStudent was destroyed but the fragment still loading the data from database, therefore the error occurs.

I try to get the mDbStudent in the Fragment when onAttach , but when I move the pages very fast, it log stated I didn't close the mDbStudent

My question is Is there a way to handle the mDbStudent when orientation change?

Answer 1

You'll need to instantiate your database outside of the Activity. Most likely, you'll be using the database in many Activies and Fragments, right? You can create a static singleton, like this:

public class Global {
    private static Global instance = null;
    private Context context;

    public Global( Context context ) {
        this.context = context.getApplicationContext();
    }

    public static getInstance( Context context ) {
        if( instance == null )
            instance = new Global( context );
        return instance;
    }

    public SQLiteOpenHelper getDatabase() {
        return ... ;
    }
}

Then, in your Activity, you can call:

Global.getInstance( this ).getDatabase()...

This stores the application's Context, so you can access that in Global instance whereever needed... even if the Activity has since been destroyed.

This will also allow you to open the database once and keep it open, even through orientation changes. In my apps, I generally leave the DB open until the app is closed explicitly. If you have a single-Activity app, I would open the database, if closed, in onStart and close it in onUserLeaveHint() . This will only close the database if the use leaves the app, but not on orientation changes.