Changing number of columns with GridLayoutManager and RecyclerView

Try handling this inside your onCreateView method instead since it will be called each time there's an orientation change:

if(getActivity().getResources().getConfiguration().orientation == Configuration.ORIENTATION_PORTRAIT){
     mRecycler.setLayoutManager(new GridLayoutManager(mContext, 2));
}
else{
     mRecycler.setLayoutManager(new GridLayoutManager(mContext, 4));
}

If you have more than one condition or use the value in multiple places this can go out of hand pretty fast. I suggest to create the following structure:

res
  - values
    - dimens.xml
  - values-land
    - dimens.xml

with res/values/dimens.xml being:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <integer name="gallery_columns">2</integer>
</resources>

and res/values-land/dimens.xml being:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <integer name="gallery_columns">4</integer>
</resources>

And the code then becomes (and forever stays) like this:

final int columns = getResources().getInteger(R.integer.gallery_columns);
mRecycler.setLayoutManager(new GridLayoutManager(mContext, columns));

You can easily see how easy it is to add new ways of determining the column count, for example using -w500dp/-w600dp/-w700dp resource folders instead of -land.

It's also quite easy to group these folders into separate resource folder in case you don't want to clutter your other (more relevant) resources:

android {
    sourceSets.main.res.srcDir 'src/main/res-overrides' // add alongside src/main/res
}