App crashes on lock/sleep screen - NullPointerException

Question

Using a device for testing - Whenever I lock the screen (or sleeps after 1 min idle), the app crashes and the logcat shows a NullPointerException always on an imageView.setOnClickListener in the onResume() method.

Here's the small part of the code where I get the exception :

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.critical_items_list);

    // instantiate member variables

    mExtras = getIntent().getExtras();
    mItems_P1 = mExtras.getParcelableArrayList(EXTRA_ITEMS_P1);
    mItems_P2 = mExtras.getParcelableArrayList(EXTRA_ITEMS_P2);
    mItems_Engine = mExtras.getParcelableArrayList(EXTRA_ITEMS_ENGINE); 
}

protected void onResume() {
    super.onResume();

    ImageView imageAddToMultiple = (ImageView) findViewById(R.id.image_add_to_multiple);

    //This is where the I get the NullPointer
    imageAddToMultiple.setOnClickListener(listenerAddToMultipleItems); 

    refreshLists();
    ListView listP1 = (ListView) findViewById(R.id.list_p1);
    ListView listP2 = (ListView) findViewById(R.id.list_p2);
    ListView listEngine = (ListView) findViewById(R.id.list_engine);

    listP1.setAdapter(new MyAdapter(mList_P1));
    listP2.setAdapter(new MyAdapter(mList_P2));
    listEngine.setAdapter(new MyAdapter(mList_Engine));
}

The imageView itself lies in a RelativeLayout:

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

<LinearLayout
    android:layout_width="fill_parent"
    android:layout_height="@dimen/standard_bar_height"
    android:background="@color/green"
    android:baselineAligned="false" >

    <LinearLayout
        android:layout_width="0dp"
        android:layout_height="fill_parent"
        android:layout_weight="1"
        android:gravity="center" >

        <TextView
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:gravity="center"
            android:text="@string/plant_1"
            android:textColor="@android:color/black" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="0dp"
        android:layout_height="fill_parent"
        android:layout_weight="1"
        android:gravity="center" >

        <TextView
            android:layout_width="fill_parent"
            android:layout_height="match_parent"
            android:layout_gravity="center"
            android:gravity="center"
            android:text="@string/plant_2"
            android:textColor="@android:color/black" />
    </LinearLayout>

    <RelativeLayout
        android:id="@+id/RelativeLayout1"
        android:layout_width="0dp"
        android:layout_height="fill_parent"
        android:layout_weight="1" >

        <ImageView
            android:id="@+id/image_add_to_multiple"
            android:layout_width="@dimen/standard_bar_height"
            android:layout_height="@dimen/standard_bar_height"
            android:layout_alignParentRight="true"
            android:layout_centerHorizontal="true"
            android:contentDescription="@string/description_add_to_multiple_items"
            android:src="@android:drawable/ic_menu_add" />

        <TextView
            android:id="@+id/TextView1"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_centerInParent="true"
            android:gravity="center"
            android:text="@string/engine"
            android:textColor="@android:color/black" />
    </RelativeLayout>
</LinearLayout>

<LinearLayout
    android:id="@+id/linearLayout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="horizontal" >

        <ListView
            android:id="@+id/list_p1"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1" >
        </ListView>

        <View
            android:layout_width="2dp"
            android:layout_height="fill_parent"
            android:background="@color/green" />

        <ListView
            android:id="@+id/list_p2"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1" >
        </ListView>

        <View
            android:layout_width="2dp"
            android:layout_height="fill_parent"
            android:background="@color/green" />

        <ListView
            android:id="@+id/list_engine"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1" >
        </ListView>
    </LinearLayout>
</LinearLayout>

I have no clue why I'm getting this NullPointer.

FATAL EXCEPTION: main java.lang.RuntimeException: Unable to resume activity {nmw.nss/nmw.nss.CriticalList}: java.lang.NullPointerException at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2820) at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2859) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2242) at android.app.ActivityThread.access$600(ActivityThread.java:139) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1262) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:4974) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException at nmw.nss.CriticalList.onResume(CriticalList.java:93)

at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1236) at android.app.Activity.performResume(Activity.java:4620) at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2804) ... 12 more

Thanks.

EDIT : I've added the complete activity(sort of), the xml, and the logcat. Do I need to override any of Activity methods, perhaps the onStop or onPause to make this work?

Answer 1

Finally found it! My app is basically designed to run in landscape mode, and in the manifest I've added ------- android:screenOrientation="landscape".

Well, here's the problem : it doesn't matter in what mode you lock the device, findViewById() always searches the XML in the portrait mode, and in my case, which did not have the ImageView at all. Hence the NullPointerException.