CircularRecyclerView.java

import android.content.Context;
import android.support.v4.view.ViewCompat;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.RecyclerView.OnScrollListener;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.AbsListView;
import android.widget.ListView;
import android.widget.TextView;


public class CircleListView extends RecyclerView {

    private static final String TAG = CircleListView.class.getSimpleName();
    private static final boolean DEBUG = BuildConfig.DEBUG && false;

    private static final int DEFAULT_SCROLL_DURATION = 200;

    public static final int DEFAULT_SELECTION = Integer.MAX_VALUE / 2;

    private boolean mIsForceCentering;

    private ViewModifier mViewModifier;


    private final CenterRunnable mCenterRunnable = new CenterRunnable();
    private int mScrollDuration = DEFAULT_SCROLL_DURATION;
    private OnItemCenteredListener mOnItemCenteredListener;

    public CircleListView(Context context, AttributeSet attrs) {
        super(context, attrs);
        setOnScrollListener(new OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
                if (newState == RecyclerView.SCROLL_STATE_IDLE) {

                    if (!mIsForceCentering) {
                        // Start centering the view

                        mIsForceCentering = true;

                        final View childView = findViewAtCenter();

                        if (childView != null) {
                            if (DEBUG) {
                            }

                            if (mOnItemCenteredListener != null) {
                                mOnItemCenteredListener.onItemCentered(childView);
                            }

                            mCenterRunnable.setView(childView);
                            ViewCompat.postOnAnimation(CircleListView.this, mCenterRunnable);
                        }
                    }
                }
            }

            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
                if (mViewModifier != null) {

                    final int count = getChildCount();
                    for (int i = 0; i < count; ++i) {
                        View v = getChildAt(i);

                        mViewModifier.applyToView(v, CircleListView.this);
                    }
                }
            }
        });
        setOverScrollMode(RecyclerView.OVER_SCROLL_NEVER);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        this.smoothScrollToPosition(DEFAULT_SELECTION);
    }

    /**
     * Sets the current {@link ViewModifier} for this list.
     *
     * @param modifier implementation of the {@link ViewModifier} class
     * @see ViewModifier
     */
    public void setViewModifier(ViewModifier modifier) {
        mViewModifier = modifier;
    }

    /**
     * Sets the smooth scroll duration.
     *
     * @param duration the number of milliseconds the scrolling animation will take
     */
    public void setScrollDuration(int duration) {
        mScrollDuration = duration;
    }

    /**
     * Sets the listener object that will be notified when the list centers on an item.
     *
     * @param listener the {@link OnItemCenteredListener} implementation
     */
    public void setOnItemCenteredListener(OnItemCenteredListener listener) {
        mOnItemCenteredListener = listener;
    }


    public void smoothScrollToView(View v) {
        final float y = v.getY() + v.getHeight() * 0.5f;
        final float halfHeight = getHeight() * 0.5f;
        final int distance = (int) (y - halfHeight);

        smoothScrollBy(distance, mScrollDuration);
    }


    @Override
    public boolean onTouchEvent(MotionEvent ev) {

        removeCallbacks(mCenterRunnable);

        mIsForceCentering = false;

        return super.onTouchEvent(ev);
    }

    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {

    }

    /**
     * Finds a View located at the specified point.
     *
     * @param x x-coordinate of the point
     * @param y y-coordinate of the point
     * @return {@link View} located at (x, y) or <code>null</code> if not found
     */
    public View findViewAt(int x, int y) {
        final int count = getChildCount();
        for (int i = 0; i < count; ++i) {
            final View v = getChildAt(i);
            final int x0 = v.getLeft();
            final int y0 = v.getTop();
            final int x1 = v.getWidth() - x0;
            final int y1 = v.getHeight() + y0;

            if (x >= x0 && x <= x1 && y >= y0 && y <= y1) {
                return v;
            }
        }

        return null;
    }

    /**
     * Finds a {@link View} located in the center of the {@link CircleListView}.
     *
     * @return the {@link View} at the center of the {@link CircleListView}
     */
    public View findViewAtCenter() {
        return findViewAt(0, getHeight() / 2);
    }

    public class CenterRunnable implements Runnable {

        private View mView;

        public void setView(View v) {
            mView = v;
        }

        public void run() {
            smoothScrollToView(mView);

            mIsForceCentering = true;
        }
    }

    /**
     * Handles the event occurring when the list centers on an item.
     *
     * @see CircleListView#setOnItemCenteredListener(OnItemCenteredListener)
     */
    public interface OnItemCenteredListener {
        public void onItemCentered(View v);
    }
}