findViewById on RecyclerView always null

Question

I have the following segment of code in a Fragment:

 @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View root = inflater.inflate(R.layout.fragment_smartzone_category, container, false);

    final Context context = getActivity();

    mPresenter = new SmartzonePresenter(context, this);
    //
    mProgressBar = (ProgressBar) root.findViewById(R.id.spinner);
    mProgressBar.setVisibility(View.VISIBLE);

    // set list
    mStaggeredLayoutManager = new StaggeredGridLayoutManager(1, StaggeredGridLayoutManager.VERTICAL);
    mStaggeredLayoutManager.setSpanCount(3);

    mRecyclerView = (RecyclerView) root.findViewById(R.id.smartzonecategorylist);
    mRecyclerView.setLayoutManager(mStaggeredLayoutManager);
    mRecyclerView.setVisibility(View.INVISIBLE);;

    // display list
    mListAdapter = new VideoCategoryAdapter(context, mCategories);
    mRecyclerView.setAdapter(mListAdapter);
    mListAdapter.setOnItemClickListener(new VideoCategoryAdapter.OnItemClickListener() {
        @Override
        public void onItemClick(View view, int position) {
            // get the category
            VideoCategory vc = mListAdapter.getItem(position);
            // display the sub-smartzone category page
            mCallback.onSelectCategory(vc, mCategories);
        }
    });

    //
    retrieveVideoList();

    return root;
}

Where mRecyclerView is declared at the header of the Fragment class.

The layout corresponds to this XML file:

<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="8dp">

<ProgressBar
    android:id="@id/spinner"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    style="?android:attr/progressBarStyle"
    android:layout_centerInParent="true" />

<android.support.v7.widget.RecyclerView
    android:id="@+id/smartzonecategorylist"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />
</FrameLayout>

However after cleaning/rebuilding and the likes I continuously receive this Logcat error:

 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
                                                                         at com.kidmixapp.commoncode.fragments.SmartzoneCategoryFragment.onCreateView(SmartzoneCategoryFragment.java:125)

Which refers to this line:

mRecyclerView.setLayoutManager(mStaggeredLayoutManager);

I also did some evaluation with debugging lines to see what root.findViewById(R.id.smartzonecategorylist); returned, and it is null?

I am not sure what is causing this. Other searches on similar issues have yielded no fixes I could find.

FIX:

It appears changing the XML Layout to refer to @id/android:list and change the findViewById to findViewById(android.R.id.list); like such fixed it. I do not know why.

NEW XML:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1">

<ProgressBar
    android:id="@id/spinner"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerInParent="true"/>

<android.support.v7.widget.RecyclerView
    android:id="@id/android:list"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

</RelativeLayout>

NEW FRAGMENT ONCREATEVIEW

 @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View root = inflater.inflate(R.layout.fragment_smartzone_category, container, false);

    final Context context = getActivity();

    mPresenter = new SmartzonePresenter(context, this);
    //
    mProgressBar = (ProgressBar) root.findViewById(R.id.spinner);
    mProgressBar.setVisibility(View.VISIBLE);

    // set list
    mStaggeredLayoutManager = new StaggeredGridLayoutManager(1, StaggeredGridLayoutManager.VERTICAL);
    mStaggeredLayoutManager.setSpanCount(3);

    mRecyclerView = (RecyclerView) root.findViewById(android.R.id.list);
    mRecyclerView.setLayoutManager(mStaggeredLayoutManager);
    mRecyclerView.setVisibility(View.INVISIBLE);;

    // display list
    mListAdapter = new VideoCategoryAdapter(context, mCategories);
    mRecyclerView.setAdapter(mListAdapter);
    mListAdapter.setOnItemClickListener(new VideoCategoryAdapter.OnItemClickListener() {
        @Override
        public void onItemClick(View view, int position) {
            // get the category
            VideoCategory vc = mListAdapter.getItem(position);
            // display the sub-smartzone category page
            mCallback.onSelectCategory(vc, mCategories);
        }
    });

    //
    retrieveVideoList();

    return root;
}

is your `smartzonecategorylist` belong to `fragment_smartzone_category` layout — Iamat8, Mar 02 '16 at 05:54
@BurhanuddinRashid I mention that I have tried this several times. No luck. — Timothy Frisch, Mar 02 '16 at 06:03
@Tukajo Are you sure that you have inflated the correct layout for this fragment? — Rethinavel, Mar 02 '16 at 06:06
I am sure that I am "trying" to inflate the correct layout. Let me see if it is even going through. — Timothy Frisch, Mar 02 '16 at 06:07
@BurhanuddinRashid, does `RecyclerView` have to use a layout with id of `@id/android:list` to work properly? — Timothy Frisch, Mar 02 '16 at 06:43
Have you imported the correct RecyclerView in your fragment just like in XML android.support.v7.widget.RecyclerView ??? — Anuj Sharma, Mar 02 '16 at 06:51
@AnujSharma I made it work with my latest post. But I don't know why it works, do you know why it is the case I have to use `@id/android:list`? — Timothy Frisch, Mar 02 '16 at 07:04
No its not necessary,you can set your own id in `androd:id="@+id/youridname"` its should work like that...can post your full xml? — Burhanuddin Rashid, Mar 02 '16 at 07:06
That is the full XML. Also it is working now and all I changed was what was stated above. So it appears that unless I use `@id/android:list` it will not work. I tried my own id. — Timothy Frisch, Mar 02 '16 at 07:08
@Tukajo you should check this post related to @id/ and @+id/ http://stackoverflow.com/q/11160954/2022000 it will help you surely — Anuj Sharma, Mar 02 '16 at 07:09
@AnujSharma I have read that before, I understand the differences between the two. I just don't know why in this specific case with RecyclerView I am not allowed to use my own defined/set id value. It is odd. — Timothy Frisch, Mar 02 '16 at 07:10

score -1 · Answer 1 · answered Mar 02 '16 at 05:53

-1

In your layout XML,your code is:

<ProgressBar
android:id="@id/spinner"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
style="?android:attr/progressBarStyle"
android:layout_centerInParent="true" />

But I think the code Should Be:

<ProgressBar
android:id="@+id/spinner"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
style="?android:attr/progressBarStyle"
android:layout_centerInParent="true" />

answered Mar 02 '16 at 05:53

李茂杰

7
2

I will change this, however will this cause the issue since the `RecyclerView` is throwing the `null`? – Timothy Frisch Mar 02 '16 at 05:54
What is the difference between both ? – M D Mar 02 '16 at 06:02
When I made this change; I now get a nullpointer error at both findViewById(R.id.spinner); and my other error. It appears changing it to "@+id" causes the null, any ideas why? – Timothy Frisch Mar 02 '16 at 06:03

findViewById on RecyclerView always null

1 Answers1