Why am I getting a null reference on my RecyclerView

Question

I am trying to use the RecyclerView in my fragments. It shows up fine for the first tab, but when I swipe to the second tab and then back to the first one I get the following er

Answer 1

Basically, the LayoutManager is being disposed of before your recycler has finished with it.

From the Android source :

@Override
protected void onDetachedFromWindow() {
    super.onDetachedFromWindow();
    if (mItemAnimator != null) {
        mItemAnimator.endAnimations();
    }
    mFirstLayoutComplete = false;
    stopScroll();
    mIsAttached = false;
    if (mLayout != null) {
        mLayout.onDetachedFromWindow(this, mRecycler);
    }
    removeCallbacks(mItemAnimatorRunner);
}

The problem stems from when the stopScroll and it tries to call mLayout.stopSmoothScroller(); without checking if mLayout is null.

I threw togeather a very hacky hot fix for an app I've been working on, but I wouldn't suggest using this for a long term solution as it's very much a bodge. If like me you have a tight deadline it's best to just catch the null pointer exception and ignore it.

My hot fix was just to create a custom View extending the RecyclerView :

import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;

public class HotFixRecyclerView extends RecyclerView
{
    public HotFixRecyclerView( Context context )
    {
        super( context );
    }

    public HotFixRecyclerView( Context context, AttributeSet attrs )
    {
        super( context, attrs );
    }

    public HotFixRecyclerView( Context context, AttributeSet attrs, int defStyle )
    {
        super( context, attrs, defStyle );
    }

    @Override
    public void stopScroll()
    {
        try
        {
            super.stopScroll();
        }
        catch( NullPointerException exception )
        {
            /**
             *  The mLayout has been disposed of before the 
             *  RecyclerView and this stops the application 
             *  from crashing.
             */
        }
    }
}

Then change all references from the RecyclerView to HotFixRecyclerView. If you do use it please remove it once Android have patched this issue as it's a bit of a hack.

• If you use recylerview inn XML don't forget to change your XML files accordingly to use com.your.package.HotFixRecyclerView instead of android.support.v7.widget.RecyclerView