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POWhy would I ever want `setRetainInstance(false)`? - Or - The correct way to handle device rotation
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copied!<p><em>Please correct me if I'm wrong on any of this. This is a kind of clarifying question since I haven't seen it explicitly written anywhere.</em></p> <p>In Android 4, you can call <code>setRetainInstance(true)</code> on a <code>Fragment</code> so that on configuration changes (which basically means device rotation), the <code>Fragment</code> java object isn't destroyed and a new instance of it isn't created. That is, the instance is retained.</p> <p>This is much more sane and less infuriating than in Android 1-3 since you don't have to deal with <code>onRetainNonConfiguration</code><strike><code>State</code></strike><code>Instance()</code> and bundle up all your data so it can be passed to the new <code>Fragment</code> (or <code>Activity</code>) instance only to be unbundled again. It's basically what you would expect to happen, and arguably how it should have worked for <code>Activity</code>s from the beginning.</p> <p>With <code>setRetainInstance(true)</code> the view is also recreated (<code>onCreateView()</code> is called) on rotation as you would expect. And I assume (not tested) that resource resolution (<code>layout</code> vs <code>layout-land</code>) works.</p> <p>So my question is two-fold:</p> <ol> <li>Why wasn't it like this with <code>Activities</code> from the beginning.</li> <li>Why isn't this the default? Is there ever any reason why you <em>would</em> actually want your <code>Fragment</code> to be pointlessly destroyed and recreated on rotation? Because I can't think of any.</li> </ol> <h1>Edit</h1> <p>To clarify how I would do it:</p> <pre><code>class MyFragment extends Fragment { // All the data. String mDataToDisplay; // etc. // All the views. TextView mViewToDisplayItIn; // etc. @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setRetainInstance(true); mDataToDisplay = readFromSomeFileOrWhatever(); // Ignoring threading issues for now. } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { return inflater.inflate(R.layout.my_fragment, container, false); } @Override public void onViewCreated(View view, Bundle savedInstanceState) { // At this point if mViewToDisplayItIn was not null, the old one will be GC'd. mViewToDisplayItIn = view.findViewById(R.id.the_text_view); mViewToDisplayItIn.setText(mDataToDisplay); } // Optionally: @Override public void onDestroyView() { // All the view (and activity) to be GC'd. mViewToDisplayItIn = null; } } </code></pre>

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