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PONull Pointer when trying to dynamically disable a preference
 

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  1. PONull Pointer when trying to dynamically disable a preference
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    <p>I am getting a null pointer exception on <code>mPreference = (Preference)...</code> in the following code (i.e. with debugger on, <code>mPreference</code> shows null; NB key is non-null, I can substitute with a literal and it still gives me the same exception):</p> <pre><code>public class SettingsManager extends PreferenceActivity { private Preference mPreference; private static boolean toggle; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // Load the XML preferences file addPreferencesFromResource(R.xml.preferences); } public void setPrefEnabled(Context context, String key, String enabled) { if (enabled.contentEquals("true")) { toggle = true; } else { toggle = false; } mPreference = (Preference) getPreferenceScreen().findPreference(key); mPreference.setEnabled(toggle); } } </code></pre> <p>The class is being called by the following code, in the <code>applySettings</code> method of a class where <code>settingsManager</code> is instantiated in the constructor:</p> <pre><code>public class ConfigurationSetter { private static Context mContext; private static SettingsManager settingsManager; public ConfigurationSetter(Context context) { mContext = context; settingsManager = new SettingsManager(); } private static void applySettings(Context context, String key, String value, String enabled) { settingsManager.setPrefEnabled(mContext, key, enabled); } } </code></pre> <p>I've been scratching my head on this but may be a little too tired to figure it out on my own. Any help is appreciated.</p> <p>Related to this problem, I <a href="https://stackoverflow.com/questions/10423709/are-intents-required-to-persist-preference-state-in-a-headless-activity">asked a question here</a> about whether intents are the required instantiater for this activity.</p>
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    1. USCommunity
    1. USh3ky1
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    1. COIs the NPE happening in the `getPreferenceScreen()` call or the `findPreference()` call? Are you sure `key` is non-null if `findPreference()` requires a non-null input?
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      1. USQuantumMechanic
    2. CO@QuantumMechanic I updated the post to respond to your quesitons
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      1. USh3ky1
    3. COgetPreferenceScreen() is probably returning null, you then try to call a method of this null.
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      1. USChris Stratton
 

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