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POShowing specified page when view pager is first created
 

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  1. POShowing specified page when view pager is first created
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    <p>I have a fragment that contains a <code>ViewPager</code>. This <code>ViewPager</code> is backed by a <code>PagerAdapter</code> that uses a <code>Cursor</code>. The cursor is managed by <code>LoaderCallbacks</code>. I'm using the v4 support libraries here.</p> <p>What I want is to create the fragment and have the view pager showing a specified page, rather than starting at page 0.</p> <p>I know that <code>ViewPager</code> has a <code>setCurrentItem()</code> method, but the data may not yet be loaded when the <code>ViewPager</code> is created. What I need is to listen to the adapter for data set changes, and if that is the first such change, then call <code>setCurrentItem()</code> on <code>ViewPager</code>.</p> <p>However the <code>PagerAdapter</code> class does not export the <code>registerDataSetObserver()</code> method; it has <code>package</code> rather than <code>public</code> access (at least in the v4 support library).</p> <p>What I have done, and it seems very much like a hack to me, is the following:</p> <pre><code>class ItemPagerFragment extends SherlockFragment implements LoaderCallbacks&lt;Cursor&gt; { private CursorPagerAdapter mAdapter; private ViewPager mPager; private int mInitialPageToShow; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); mAdapter = new CursorPagerAdapter() { @Override public void notifyDataSetChanged() { super.notifyDataSetChanged(); setInitialPageIfRequired(); } }; getActivity().getSupportLoaderManager().initLoader(LOADER_ID, null, this); } @Override public View onCreateView(LayoutInflater inflater, ViewGroup group, Bundle saved) { View view = inflater.inflate(R.layout.items_pager, group, false); mPager = (ViewPager) view.findViewById(R.id.pager); mPager.setAdapter(mAdapter); setInitialPageIfRequired(); return view; } private boolean initialPageSet = false; private synchronized void setInitialPageIfRequired() { // Set the current page of the pager if (a) this is the // first time attempting to set the page and (b) the // pager exists and (c) the adapter has data. if (!initialPageSet &amp;&amp; mPager != null &amp;&amp; mAdapter.getCount() &gt; 0) { mPager.setCurrentItem(mInitialPageToShow); initialPageSet = true; } } } </code></pre> <p>There's a race condition between loading data into the adapter (in the <code>onCreate()</code> method), and creating the <code>ViewPager</code> in the <code>onCreateView()</code> method. So the current page can be set either when (a) the pager exists but data is loaded for the first time or (b) the data is loaded before the pager is created.</p> <p>I've tried to handle both cases above but I'm thinking there must be an alternative approach that is more robust (and hopefully simpler) using observers.</p>
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    1. USJohn Q Citizen
    1. USJohn Q Citizen
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      1. POShowing specified page when view pager is first created
      1. USMuthuraj
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      1. UStinesoft
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    1. COCan you post the code for `CursorPagerAdapter`?
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      1. USLuksprog
    2. CO@Luksprog The `CursorPagerAdapter` class extends `FragmentPagerAdapter` and handles `getCount()` and `getItem()` using a cursor. It also has a `swapCursor()` method (cf `CursorAdapter` class) that is called by the `LoaderCallbacks` methods (not shown in my code snippets above). I've put the `CursorPagerAdapter` code on pastebin here: http://pastebin.com/XTx5HfKS
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      1. USJohn Q Citizen
    3. COIf I would be in your place I would start the `Fragments` from the `ViewPager` with what data I have at that moment(if I don't have any just show a blank something, or loading) and in the loader's `onLoadFinished` callback I would put the data in a field in the master `Fragment` and let the `ViewPager` fragment know that data is available for them and that they should update.
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      1. USLuksprog
 

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