How can a divider line be added in an Android RecyclerView?

Question

In the October 2016 update, the support library v25.0.0 now has a default implementation of basic horizontal and vertical dividers available!

https://developer.android.com/reference/android/support/v7/widget/DividerItemDecoration.html

 recyclerView.addItemDecoration(new DividerItemDecoration(recyclerView.getContext(), DividerItemDecoration.VERTICAL));

The Right way is to define ItemDecoration for the RecyclerView is as following

SimpleDividerItemDecoration.java

public class SimpleDividerItemDecoration extends RecyclerView.ItemDecoration {
    private Drawable mDivider;
 
    public SimpleDividerItemDecoration(Context context) {
        mDivider = ContextCompat.getDrawable(context, R.drawable.line_divider);
    }
 
    @Override
    public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
        int left = parent.getPaddingLeft();
        int right = parent.getWidth() - parent.getPaddingRight();
 
        int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            View child = parent.getChildAt(i);
 
            RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
 
            int top = child.getBottom() + params.bottomMargin;
            int bottom = top + mDivider.getIntrinsicHeight();
 
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }
}

Or If you are using kotlin: SimpleDividerItemDecoration.kt

class SimpleDividerItemDecoration(context: Context, @DrawableRes dividerRes: Int) : ItemDecoration() {

    private val mDivider: Drawable = ContextCompat.getDrawable(context, dividerRes)!!

    override fun onDrawOver(c: Canvas, parent: RecyclerView) {
        val left = parent.paddingLeft
        val right = parent.width - parent.paddingRight
        val childCount = parent.childCount
        for (i in 0 until childCount) {
            val child: View = parent.getChildAt(i)
            val params = child.layoutParams as RecyclerView.LayoutParams
            val top: Int = child.bottom + params.bottomMargin
            val bottom = top + mDivider.intrinsicHeight
            mDivider.setBounds(left, top, right, bottom)
            mDivider.draw(c)
        }
    }
}
    

line_divider.xml:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
 
    <size
        android:width="1dp"
        android:height="1dp" />
 
    <solid android:color="@color/dark_gray" />
 
</shape>

Finally set it like this

recyclerView.addItemDecoration(new SimpleDividerItemDecoration(this));

---

Edit

As pointed by @Alan Solitar

context.getResources().getDrawable(R.drawable.line_divider); 

is depreciated instead of that you can use

ContextCompat.getDrawable(context,R.drawable.line_divider);

If you want to have both horizontal and vertical dividers:

1. Define horizontal & vertical divider drawables:

   horizontal_divider.xml

   <?xml version="1.0" encoding="utf-8"?>
   <shape xmlns:android="http://schemas.android.com/apk/res/android" >
     <size android:height="1dip" />
     <solid android:color="#22000000" />
   </shape>
   

   vertical_divider.xml

   <?xml version="1.0" encoding="utf-8"?>
   <shape xmlns:android="http://schemas.android.com/apk/res/android" >
       <size android:width="1dip" />
       <solid android:color="#22000000" />
   </shape>
   

2. Add this code segment below:

   DividerItemDecoration verticalDecoration = new DividerItemDecoration(recyclerview.getContext(),
           DividerItemDecoration.HORIZONTAL);
   Drawable verticalDivider = ContextCompat.getDrawable(getActivity(), R.drawable.vertical_divider);
   verticalDecoration.setDrawable(verticalDivider);
   recyclerview.addItemDecoration(verticalDecoration);
   
   DividerItemDecoration horizontalDecoration = new DividerItemDecoration(recyclerview.getContext(),
           DividerItemDecoration.VERTICAL);
   Drawable horizontalDivider = ContextCompat.getDrawable(getActivity(), R.drawable.horizontal_divider);
   horizontalDecoration.setDrawable(horizontalDivider);
   recyclerview.addItemDecoration(horizontalDecoration);
   

All of these answers got me close but they were each missing a key detail. After a bit of research, I found the easiest route to be a combination of these 3 steps:

1. Use the support library's DividerItemDecoration
2. Create a divider with the right color
3. Set this divider in your theme as the listDivider

---

Step 1: while configuring RecyclerView

recyclerView.addItemDecoration(
        new DividerItemDecoration(context, layoutManager.getOrientation()));

Step 2: in a file like res/drawable/divider_gray.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <size android:width="1px" android:height="1px" />
    <solid android:color="@color/gray" />
</shape>

Step 3: in the app's theme

<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <!-- Other theme items above -->
    <item name="android:listDivider">@drawable/divider_gray</item>
</style>

---

EDIT: Updated to skip last divider:
After using this a bit, I realized it was drawing a divider after the last item, which was annoying. So I modified Step 1 as follows to override that default behavior in DividerItemDecoration (of course, making a separate class is another option):

recyclerView.addItemDecoration(
        new DividerItemDecoration(context, layoutManager.getOrientation()) {
            @Override
            public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
                int position = parent.getChildAdapterPosition(view);
                // hide the divider for the last child
                if (position == parent.getAdapter().getItemCount() - 1) {
                    outRect.setEmpty();
                } else {
                    super.getItemOffsets(outRect, view, parent, state);
                }
            }
        }
);

Just add a View by the end of you item adapter:

<View
 android:layout_width="match_parent"
 android:layout_height="1dp"
 android:background="#FFFFFF"/>

Here is the code for a simple custom divider (vertical divider / 1dp height / black ):

It suppose you have Support Library:

compile "com.android.support:recyclerview-v7:25.1.1"

java code

    DividerItemDecoration divider = new DividerItemDecoration(recyclerView.getContext(), DividerItemDecoration.VERTICAL);
    divider.setDrawable(ContextCompat.getDrawable(getBaseContext(), R.drawable.my_custom_divider));
    recyclerView.addItemDecoration(divider);

then the custom_divider.xml file sample :

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="rectangle">
    <size android:height="1dp" />
    <solid android:color="@android:color/black" />
</shape>