Question

What I have Gives Me these errors.

04-13 15:01:41.600: E/AndroidRuntime(8431): FATAL EXCEPTION: main
04-13 15:01:41.600: E/AndroidRuntime(8431): java.lang.RuntimeException: Unable to start activity ComponentInfo    {com.omnilabs.alexandernapoles.hl2sticl/com.example.example.example.MainClass}: java.lang.NullPointerException
04-13 15:01:41.600: E/AndroidRuntime(8431):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at android.app.ActivityThread.access$600(ActivityThread.java:123)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at android.os.Looper.loop(Looper.java:137)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at android.app.ActivityThread.main(ActivityThread.java:4424)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at java.lang.reflect.Method.invokeNative(Native Method)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at java.lang.reflect.Method.invoke(Method.java:511)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:787)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:554)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at dalvik.system.NativeStart.main(Native Method)
04-13 15:01:41.600: E/AndroidRuntime(8431): Caused by: java.lang.NullPointerException
04-13 15:01:41.600: E/AndroidRuntime(8431):     at android.content.ContextWrapper.getPackageName(ContextWrapper.java:127)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at android.preference.PreferenceManager.getDefaultSharedPreferencesName    (PreferenceManager.java:371)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at android.preference.PreferenceManager.getDefaultSharedPreferences    (PreferenceManager.java:366)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at com.example.example.example.ShakeEventListener.<init>(ShakeEventListener.java:24)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at com.example.example.example.MainClass.onCreate(StunBatton.java:38)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at android.app.Activity.performCreate(Activity.java:4465)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
04-13 15:01:41.600: E/AndroidRuntime(8431):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
04-13 15:01:41.600: E/AndroidRuntime(8431):     ... 11 more

And here is part of my shakevent listener class that involves preferences

public class ShakeEventListener extends Application implements SensorEventListener {
public void onCreate(Bundle savedInstanceState) {

    super.onCreate();


}
SharedPreferences preferences =
         PreferenceManager.getDefaultSharedPreferences(this);


private String editTextPref = getString(R.string.preference_key);
int nVar = preferences.getInt(editTextPref, MODE_PRIVATE);
int MIN_FORCE = nVar;
/**
* Minimum times in a shake gesture that the direction of movement needs to
* change.
*/
private static final int MIN_DIRECTION_CHANGE = 15;

/** Maximum pause between movements. */
private static final int MAX_PAUSE_BETHWEEN_DIRECTION_CHANGE = 50000;

etc etc

preferences.java

package com.example.example.example;

import android.os.Bundle;
import android.preference.PreferenceActivity;

public class Preferences extends PreferenceActivity {
        @Override
        protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                addPreferencesFromResource(R.layout.preferences);


        }
}

Preferences.xml

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
        <PreferenceCategory
                android:title="First Category">
        <EditTextPreference
                android:name="Stun Swing Sensitivity"
                android:summary="This allows you to custom fit your sensitivity."
                android:defaultValue="10"
               android:numeric="integer"
                android:maxLength="200"
                android:title="Sensitivity Level"
                android:key="@string/preference_key" />
        </PreferenceCategory>

</PreferenceScreen>

Inside of strings.xml i put
editTextPref

So Basically I just want to know how I can use a variable in a class file that an activity calls for shaking then it uses onShake(); to call from the shake activity, But I want to save MIN_FORCE as a variable nVar and nVar be the setting in the preference files thats an integer.

Please Help!!!!!!!!!

EDIT:
I know it has to do with this code

      SharedPreferences preferences =
             PreferenceManager.getDefaultSharedPreferences(this);
 String editTextPref = getString(R.string.preference_key);
nVar = preferences.getInt(editTextPref, 10);

Answer 1

You have to move the call to getDefaultSharedPreferences inside onCreate (or a later callback). It does not work outside because at object construction time your Activity isn’t fully set up.

public class ShakeEventListener extends Application implements SensorEventListener {

int nVar = 0;
public void onCreate(Bundle savedInstanceState) {

    super.onCreate();
    SharedPreferences preferences =
         PreferenceManager.getDefaultSharedPreferences(this);


    private String editTextPref = getString(R.string.preference_key);
    nVar = preferences.getInt(editTextPref, MODE_PRIVATE);
    int MIN_FORCE = nVar;
}