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POViewPager Cursor position
 

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  1. POViewPager Cursor position
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    <p>I am writing a simple news app as a learning exercise. Display a listfragment driven by a SQLite cursor. Click and go to detail screen. Now trying to convert detail screen to ViewPager. I do not want to pass the Cursor from listfragment to ViewPager activity, so I pass the current position in the cursor instead and then create a new Cursor. Can't seem to get the position right though. If I set it in the Activity and not getItem() it goes to the correct position but never changes. If I set it in getItem, it always starts at position 0. The key lines are </p> <pre><code>// cp.getCursor().moveToPosition(mStartPosition); // cp.notifyDataSetChanged(); </code></pre> <p>Thanks for any help.</p> <pre><code> public class ViewPagerActivity extends FragmentActivity { private static final int NUM_PAGES = 5; private static String mSectionSelected = ""; private static int mStartPosition; private ViewPager mPager; private PagerAdapter mPagerAdapter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.view_pager); // Instantiate a ViewPager and a PagerAdapter. mSectionSelected = (String)this.getIntent().getSerializableExtra("SECTION"); mPager = (ViewPager) this.findViewById(R.id.pager); CursorPagerAdapter cp = new CursorPagerAdapter( getSupportFragmentManager(), mSectionSelected); mPager.setAdapter(cp); // cp.getCursor().moveToPosition(mStartPosition); // cp.notifyDataSetChanged(); } @Override public void onBackPressed() { if (mPager.getCurrentItem() == 0) { // If the user is currently looking at the first step, allow the system to handle the // Back button. This calls finish() on this activity and pops the back stack. super.onBackPressed(); } else { // Otherwise, select the previous step. mPager.setCurrentItem(mPager.getCurrentItem() - 1); } } } </code></pre> <p>And here is the adapter - the key line is <code>cursor.moveToPosition(position);</code></p> <pre><code> public class CursorPagerAdapter extends FragmentStatePagerAdapter { private Cursor cursor; private static String mSectionSelected; public CursorPagerAdapter(FragmentManager fm, String mSection) { super(fm); mSectionSelected = mSection; this.cursor = NewsManager.get(ApplicationContext.getInstance()).queryNews(mSectionSelected); } @Override public PagerDetailFragment getItem(int position) { if (cursor == null) // shouldn't happen return null; cursor.moveToPosition(position); PagerDetailFragment frag; try { frag = PagerDetailFragment.newInstance(); String mTitle = cursor.getString(NewsDatabaseHelper.COLNUM_TITLE); String mSection = cursor.getString(NewsDatabaseHelper.COLNUM_CATEGORY); String mSource = cursor.getString(NewsDatabaseHelper.COLNUM_SOURCE); String mPublishedDate = cursor.getString(NewsDatabaseHelper.COLNUM_PUBLISHDATE); String mThumbnail = cursor.getString(NewsDatabaseHelper.COLNUM_THUMBNAIL); String mBody = cursor.getString(NewsDatabaseHelper.COLNUM_CONTENT); Bundle args = new Bundle(); args.putString(NewsDatabaseHelper.COLUMN_TITLE, mTitle); args.putString(NewsDatabaseHelper.COLUMN_CATEGORY, mSection); args.putString(NewsDatabaseHelper.COLUMN_SOURCE, mSource); args.putString(NewsDatabaseHelper.COLUMN_PUBLISHDATE, mPublishedDate); args.putString(NewsDatabaseHelper.COLUMN_THUMBNAIL, mThumbnail); args.putString(NewsDatabaseHelper.COLUMN_CONTENT, mBody); frag.setArguments(args); } catch (Exception ex) { throw new RuntimeException(ex); } return frag; } @Override public int getCount() { if (cursor == null) return 0; else return cursor.getCount(); } public void swapCursor(Cursor c) { if (cursor == c) return; this.cursor = c; notifyDataSetChanged(); } public Cursor getCursor() { return cursor; } } </code></pre>
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    1. COyou said "I do not want to pass the Cursor from listfragment to ViewPager activity" can you elaborate? as it looks every time you touch a fragment and launch the activity you'll have to create a new Cursor and get the data again, which could be slow.
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    2. COI read a very convincing post here on SO that passing Cursor's is very dangerous - mostly because they are created in one Context and then passed to another. Here is the link: http://stackoverflow.com/questions/13774020/is-it-safe-to-pass-a-cursor-to-another-activity
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    3. COI'd look into doing something similar to what was recommended in the comments of that question's answer and do this all under 1 activity, that way you have a list bound to the cursor for data and you have a `viewPager` bound to the same instance on say a different fragment (same context as that's the activity) and just flip between them as needed.
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