StackOverflow2013

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copied!<ol> <li><p>Get rid of <code>Activity</code> from the names of all classes that do not inherit from <code>Activity</code>. For example, <code>IndexFragmentActivity</code> is not an <code>Activity</code>.</p></li> <li><p>In <code>onCreate()</code> of your actual activity, you are calling <code>findFragmentById()</code> to retrieve a fragment, then calling <code>newInstance()</code> on that fragment. However, the fragment will not exist the first time <code>onCreate()</code> is called, and you will fail here with a <code>NullPointerException</code>. Please correctly handle this case.</p></li> <li><p>The method name <code>newInstance</code> in Java is most commonly associated with the <a href="http://en.wikipedia.org/wiki/Factory_method_pattern" rel="noreferrer">factory pattern</a>, where <code>newInstance()</code> is a <code>static</code> method used in place of a public constructor to create instances of some class. Your <code>newInstance()</code> method is not <code>static</code>. This will cause confusion for those who come after you to maintain the code.</p></li> <li><p>You call <code>newInstance()</code> in <code>onCreate()</code>, create the new fragment instance, and then throw it away, which is a waste of time.</p></li> </ol> <p>Hence, assuming that your original instance of your fragment (wherever it came from) does not have an arguments <code>Bundle</code> set, that would explain your <code>NullPointerException</code> in <code>getSelectedIndex()</code>.</p> <blockquote> <p>When Im trying to pass a parameter from FragmentActivity to a Fragment</p> </blockquote> <p>To pass a parameter to a <em>newly created</em> fragment, using a <code>static</code> <code>newInstance()</code> method and the arguments <code>Bundle</code> to create the <em>new</em> fragment is perfectly reasonable.</p> <p>To pass a parameter to a fragment that already exists, simply call some setter method on that fragment.</p>

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