An ItemDecoration that draws dividers between items. Pulled from Android support demos.

DividerItemDecoration.java

/*
 * Copyright (C) 2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
public class DividerItemDecoration extends RecyclerView.ItemDecoration {

    private static final int[] ATTRS = new int[]{
            android.R.attr.listDivider
    };

    public static final int HORIZONTAL_LIST = LinearLayoutManager.HORIZONTAL;

    public static final int VERTICAL_LIST = LinearLayoutManager.VERTICAL;

    private Drawable mDivider;

    private int mOrientation;

    public DividerItemDecoration(Context context, int orientation) {
        final TypedArray a = context.obtainStyledAttributes(ATTRS);
        mDivider = a.getDrawable(0);
        a.recycle();
        setOrientation(orientation);
    }

    public void setOrientation(int orientation) {
        if (orientation != HORIZONTAL_LIST && orientation != VERTICAL_LIST) {
            throw new IllegalArgumentException("invalid orientation");
        }
        mOrientation = orientation;
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent) {
        if (mOrientation == VERTICAL_LIST) {
            drawVertical(c, parent);
        } else {
            drawHorizontal(c, parent);
        }
    }

    public void drawVertical(Canvas c, RecyclerView parent) {
        final int left = parent.getPaddingLeft();
        final int right = parent.getWidth() - parent.getPaddingRight();

        final int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            final View child = parent.getChildAt(i);
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                    .getLayoutParams();
            final int top = child.getBottom() + params.bottomMargin;
            final int bottom = top + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }

    public void drawHorizontal(Canvas c, RecyclerView parent) {
        final int top = parent.getPaddingTop();
        final int bottom = parent.getHeight() - parent.getPaddingBottom();

        final int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            final View child = parent.getChildAt(i);
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                    .getLayoutParams();
            final int left = child.getRight() + params.rightMargin;
            final int right = left + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }

    @Override
    public void getItemOffsets(Rect outRect, int itemPosition, RecyclerView parent) {
        if (mOrientation == VERTICAL_LIST) {
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        } else {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
        }
    }
}

At line 58 possible to be used childCount-1 to avoid drawing divider after last item in list

I wonder if it is a good idea to use Paint instead of bothering creating a drawable resource?
Any performance difference?

public DividerItemDecoration(Context context, int colorResId, int dividerWidthDimenResId) {
    mPaint = new Paint();
    mPaint.setColor(context.getResources().getColor(colorResId));
    mPaint.setStrokeWidth((int) context.getResources().getDimension(dividerWidthDimenResId));
}

@Override
public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
    int startX = parent.getPaddingLeft();
    int stopX = 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 y = child.getBottom() + params.bottomMargin;

        c.drawLine(startX, y, stopX, y, mPaint);
    }
}

possible bug at line 79, it should be
final int right = left + mDivider.getIntrinsicWidth();

    mDivider = a.getDrawable(0);

Returns null for 5.1.1

Also adding:

 mDivider = a.getDrawable(0);

returns a null drawable.

Also adding:
Line 79:

final int right = left + mDivider.getIntrinsicWidth();

Thanks for this code. I am using it to set the divider in a PreferenceFragmentCompat. For a PreferenceFragmentCompat I had to make a change so not to display a divider line under the last element. To do this, I changed drawVertical() and drawHorizontal():

from:

for (int i = 0; i < childCount; i++) {

to:

for (int i = 0; i < childCount-1; i++) {

Thanks.

You should not be looping over 0 to childCount (with or without the -1). You should loop from findFirstVisibleItemPosition() to findLastVisibleItemPosition(), checking them first for NO_POSITION. The last item check would then be whether the position is the last item from the adapter.

Didn't work for android 5.0 +

how i can increase divider width and height???????