NullPointerException checkbox sharedpreferences

Question

I am trying to save the values from different checkboxes located in a layout.xml file, using sharedpreferences.

But when i compile the program i get a NullPointerException, according Logcat the cause is in line 463, marked in my code.

I tried sevaral things, but i can`t get rid of the exception.

Could someone please help me?

The Exception from Logcat:

10-29 23:35:31.556: E/AndroidRuntime(3292): FATAL EXCEPTION: main 
10-29 23:35:31.556: E/AndroidRuntime(3292): java.lang.RuntimeException: Unable to resume activity {com.sencide/com.sencide.AndroidLogin}: java.lang.NullPointerException 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2241) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2256) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1789) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at android.app.ActivityThread.access$1500(ActivityThread.java:123) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:939) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at android.os.Handler.dispatchMessage(Handler.java:99) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at android.os.Looper.loop(Looper.java:130) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at android.app.ActivityThread.main(ActivityThread.java:3835) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at java.lang.reflect.Method.invokeNative(Native Method) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at java.lang.reflect.Method.invoke(Method.java:507) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:847) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at dalvik.system.NativeStart.main(Native Method) 
10-29 23:35:31.556: E/AndroidRuntime(3292): Caused by: java.lang.NullPointerException 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at com.sencide.AndroidLogin.onResume(AndroidLogin.java:463) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1150) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at android.app.Activity.performResume(Activity.java:3832) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2231) 
10-29 23:35:31.556: E/AndroidRuntime(3292):     ... 12 more 

Part of the code in my Main program xml:

On Create and set values:

public static final String PREFS_NAME = "SharedPrefsDemoPreferences"; 
public static final String PREF_BOOL = "PrefBool";
private SharedPreferences mPrefs;
private CheckBox mCheckBox;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    mPrefs = getSharedPreferences(PREFS_NAME, 0);
    mCheckBox = (CheckBox)findViewById(R.id.nieuwbel);// in layout.xml 

The OnPause and OnResume:

@Override
protected void onResume() {      
    mCheckBox.setChecked(mPrefs.getBoolean(PREF_BOOL, false)); <-- Line 463   
    super.onResume();}

@Override    
protected void onPause() { 
    Editor e = mPrefs.edit();
    e.putBoolean(PREF_BOOL, mCheckBox.isChecked());              
    e.commit();         
    Toast.makeText(this, "Settings Saved.", Toast.LENGTH_SHORT).show();        
    super.onPause();    }

The layout file with the checkbox:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >


<CheckBox
    android:id="@+id/nieuwbel"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:checked="true"
    android:text="Nieuw beltegoed" />


<CheckBox
    android:id="@+id/vorige"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:checked="true"
    android:text="Tegoed vorige periode" />

and so on...

Answer 1

You need to get SharedPreferences again. At that point mPrefs can be also null object. Also try reinstatiating the mCheckBox. This happens if the activity went from onPause() to onResume() not calling onCreate() again where you have instatiation of both object properly.

Edit:

    @Override
    protected void onResume() {      
        mPrefs = getSharedPreferences(PREFS_NAME, 0);
         mCheckBox = (CheckBox)findViewById(R.id.nieuwbel);
        if(mPrefs!=null)  //check in case there are no prefs saved, due some reason
           mCheckBox.setChecked(mPrefs.getBoolean(PREF_BOOL, false));
        else
            mCheckBox.setChecked(true); //here put default value if there are no preferences saved
        super.onResume();
}

Edit 2: Inflating the other xml.

You put this inside onResume()

LayoutInflater inflater = (LayoutInflater)getSystemService
      (Context.LAYOUT_INFLATER_SERVICE);
   View v = inflater.inflate(R.layout.layout, null); // you have the xml as a view from which you can extract the checkbox
   mCheckBox = (CheckBox)v.findViewById(R.id.nieuwbel);
   .... do the rest of the coding in the first edit :)

Answer 2

A couple of tips:

1) Make sure you check it isn't null straight after you find it.

mCheckBox = (CheckBox)findViewById(R.id.nieuwbel);
Toast.makeText(this, "Is checkbox null? " + mCheckBox, Toast.LENGTH_SHORT).show(); 

2) Separate out the line with the NullPointerException so you know which variable is null.

boolean savedValue = mPrefs.getBoolean(PREF_BOOL, false);
mCheckBox.setChecked(savedValue);

If mPrefs is null then you probably need to get the SharedPreferences again.

mPrefs = getSharedPreferences(PREFS_NAME, 0);