How to indent the divider in a linear layout RecyclerView (ie, add padding, margin, or an inset only to the ItemDecoration)

Question

Following this answer I was able to get a divider between the items of a vertical RecyclerView. However, I also wanted to slightly indent the divider lines.

I was able to do it by hard coding in an INDENT value in the RecyclerView.ItemDecoration subclass.

int INDENT = 20;

@Override
public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) { 

    int left = parent.getPaddingLeft() + INDENT;
    int right = parent.getWidth() - parent.getPaddingRight() - INDENT;

    // ...

        divider.setBounds(left, top, right, bottom);

    // ...
} 

However, then I would have had to also mess with density independant pixels.

I finally found a solution similar to how it was done with ListView so I am sharing that as an answer below.

Answer 1

Use inset

drawable/my_divider.xml

<inset xmlns:android="http://schemas.android.com/apk/res/android"
       android:insetLeft="40dp"
       android:insetRight="40dp" >

    <shape>
        <size android:height="1dp"/>
        <solid android:color="@color/recyclerview_divider" />
    </shape>

</inset>

Using the constructor that takes a resource id as shown in this answer, we can supply the id of our custom divider xml file.

Update:

We can't add drawable in DividerItemDecoration constructor, we need to set drawable after created like in the example below

ItemDecoration dividerItemDecoration = new DividerItemDecoration(
    getActivity(), 
    RecyclerView.VERTICAL
)
dividerItemDecoration.setDrawable(drawable)
recyclerView.addItemDecoration(decorator);

Drawable drawable =