RecyclerView 获取 item 的位置

/** * Created by JokAr on 2016/2/17. */public class RecyclerViewPositionHelper {    final RecyclerView recyclerView;    final RecyclerView.LayoutManager layoutManager;    public RecyclerViewPositionHelper(RecyclerView recyclerView) {        this.recyclerView = recyclerView;        this.layoutManager = recyclerView.getLayoutManager();    }    public static RecyclerViewPositionHelper createHelper(RecyclerView recyclerView) {        if (recyclerView == null) {            throw new NullPointerException("Recycler View is null");        }        return new RecyclerViewPositionHelper(recyclerView);    }    /**     * Returns the adapter item count.     *     * @return The total number on items in a layout manager     */    public int getItemCount() {        return layoutManager == null ? 0 : layoutManager.getItemCount();    }    /**     * Returns the adapter position of the first visible view. This position does not include     * adapter changes that were dispatched after the last layout pass.     *     * @return The adapter position of the first visible item or {@link RecyclerView#NO_POSITION} if     * there aren't any visible items.     */    public int findFirstVisibleItemPosition() {        final View child = findOneVisibleChild(0, layoutManager.getChildCount(), false, true);        return child == null ? RecyclerView.NO_POSITION : recyclerView.getChildAdapterPosition(child);    }    /**     * Returns the adapter position of the first fully visible view. This position does not include     * adapter changes that were dispatched after the last layout pass.     *     * @return The adapter position of the first fully visible item or     * {@link RecyclerView#NO_POSITION} if there aren't any visible items.     */    public int findFirstCompletelyVisibleItemPosition() {        final View child = findOneVisibleChild(0, layoutManager.getChildCount(), true, false);        return child == null ? RecyclerView.NO_POSITION : recyclerView.getChildAdapterPosition(child);    }    /**     * Returns the adapter position of the last visible view. This position does not include     * adapter changes that were dispatched after the last layout pass.     *     * @return The adapter position of the last visible view or {@link RecyclerView#NO_POSITION} if     * there aren't any visible items     */    public int findLastVisibleItemPosition() {        final View child = findOneVisibleChild(layoutManager.getChildCount() - 1, -1, false, true);        return child == null ? RecyclerView.NO_POSITION : recyclerView.getChildAdapterPosition(child);    }    /**     * Returns the adapter position of the last fully visible view. This position does not include     * adapter changes that were dispatched after the last layout pass.     *     * @return The adapter position of the last fully visible view or     * {@link RecyclerView#NO_POSITION} if there aren't any visible items.     */    public int findLastCompletelyVisibleItemPosition() {        final View child = findOneVisibleChild(layoutManager.getChildCount() - 1, -1, true, false);        return child == null ? RecyclerView.NO_POSITION : recyclerView.getChildAdapterPosition(child);    }    View findOneVisibleChild(int fromIndex, int toIndex, boolean completelyVisible,                             boolean acceptPartiallyVisible) {        OrientationHelper helper;        if (layoutManager.canScrollVertically()) {            helper = OrientationHelper.createVerticalHelper(layoutManager);        } else {            helper = OrientationHelper.createHorizontalHelper(layoutManager);        }        final int start = helper.getStartAfterPadding();        final int end = helper.getEndAfterPadding();        final int next = toIndex > fromIndex ? 1 : -1;        View partiallyVisible = null;        for (int i = fromIndex; i != toIndex; i += next) {            final View child = layoutManager.getChildAt(i);            final int childStart = helper.getDecoratedStart(child);            final int childEnd = helper.getDecoratedEnd(child);            if (childStart < end && childEnd > start) {                if (completelyVisible) {                    if (childStart >= start && childEnd <= end) {                        return child;                    } else if (acceptPartiallyVisible && partiallyVisible == null) {                        partiallyVisible = child;                    }                } else {                    return child;                }            }        }        return partiallyVisible;    }}