RecyclerView完美实现拖拽，滑动删除，撤销删除

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RecyclerView完美实现拖拽，滑动删除，撤销删除

本文所讲的都是使用自带 API 实现，并不借用第三方控件。用于RecyclerView 中实现滑动删除，拖拽排序，以及如何实现删除后撤销操作（类似于知乎中撤销删除操作）
- 初始化RecyclerView，绑定Adapter，LayoutManager等。

效果图
这里写图片描述

//数据mUserBookShelfResponses = new ArrayList<>();mRecyclerView =(RecyclerView)findViewById(R.id.recyclerView);mSwipeRefreshLayout = (SwipeRefreshLayout)findViewById(R.id.swipe_refresh_widget);//给刷新控件添加颜色，最多4中颜色mSwipeRefreshLayout.setColorSchemeResources(R.color.recycler_color1,R.color.recycler_color2,R.color.recycler_color3, R.color.recycler_color4);//瀑布流mLayoutManager = new StaggeredGridLayoutManager(2,StaggeredGridLayoutManager.VERTICAL);mRecyclerView.setHasFixedSize(false);mRecyclerView.setLayoutManager(mLayoutManager);//创建AdaptermBookShelfAdapter = new UserBookShelfAdapter(mUserBookShelfResponses);//设置Item增加、移除动画mRecyclerView.setItemAnimator(new DefaultItemAnimator());final int space = DensityUtils.dp2px(getActivity(), 4);//自定义一个Decoration,用于recyclerView中每一个Item之间的间隔（后面将贴出代码【附1】）mRecyclerView.addItemDecoration(new StaggeredGridDecoration(space, space, space, space));mRecyclerView.setAdapter(mBookShelfAdapter);//绑定监听事件实现上拉加载更多【附2】mRecyclerView.addOnScrollListener(new RecyclerViewScrollDetector());//监听刷新mSwipeRefreshLayout.setOnRefreshListener(this);

使用 ItemTouchHelper 工具类来处理RecyclerView中item的选中、滑动或（和）拖拽动作。
Google官方文档上是这么介绍的：
This is a utility class to add swipe to dismiss and drag & drop support to RecyclerView.
意思就是：这是一个支持RecyclerView滑动删除和拖拽的实用工具类

看看它的构造函数：

 public ItemTouchHelper(Callback callback) {        mCallback = callback;    }

我们发现这里需要一个Callback参数，进入ItemTouchHelper我们会看到有一个Callback类，集成它需要实现一些方法

        //所有动作的标志        @Override        public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {            return 0;        }        //拖拽        @Override        public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {            return false;        }        //滑动        @Override        public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {        }

我们还会发现还有一个已经被封装好了的一个SimpleCallback类，Google工程师已经为我们封装好了一些操作，让我们更简单的使用它。

ItemTouchHelper.Callback mCallback = new ItemTouchHelper.SimpleCallback(int dragDirs, int swipeDirs) {    /**     * @param recyclerView     * @param viewHolder 拖动的ViewHolder     * @param target 目标位置的ViewHolder     * @return     */    @Override    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {        //...        return false;    }    /**     * @param viewHolder 滑动的ViewHolder     * @param direction 滑动的方向     */    @Override    public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {        //...    }};

这里来解释一下构造函数SimpleCallback(int dragDirs, int swipeDirs)中的参数的含义，有一下这些可选项：

    /**     * Up direction, used for swipe & drag control.     */    public static final int UP = 1;    /**     * Down direction, used for swipe & drag control.     */    public static final int DOWN = 1 << 1;    /**     * Left direction, used for swipe & drag control.     */    public static final int LEFT = 1 << 2;    /**     * Right direction, used for swipe & drag control.     */    public static final int RIGHT = 1 << 3;

即我们对哪些方向操作关心。如果我们关心用户向上拖动，可以将dragDirs参数填充UP | DOWN ，如果我们对左右滑动感兴趣，填充swipeDirs参数为
LEFT | RIGHT 。0表示从不关心。

然后调用attachToRecyclerView()绑定动作

ItemTouchHelper touchHelper = new ItemTouchHelper(newSimpleItemTouchHelperCallback(0,ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT));//attachToRecyclerView(将动作处理监听绑定到RecyclerView中)touchHelper.attachToRecyclerView(mRecyclerView);

接下来我们看看Callback具体实现

class SimpleItemTouchHelperCallback extends ItemTouchHelper.SimpleCallback {        //保存被删除item信息，用于撤销操作        //这里使用队列数据结构，当连续滑动删除几个item时可能会保存多个item数据，并需要记录删除循序。        BlockingQueue queue = new ArrayBlockingQueue(3);        public SimpleItemTouchHelperCallback(int dragDirs, int swipeDirs) {            super(dragDirs, swipeDirs);        }        @Override        public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {            //得到拖动ViewHolder的position            int fromPosition = viewHolder.getAdapterPosition();            //得到目标ViewHolder的position            int toPosition = target.getAdapterPosition();            if (fromPosition < toPosition) {                //分别把中间所有的item的位置重新交换                for (int i = fromPosition; i < toPosition; i++) {                    Collections.swap(mUserBookShelfResponses, i, i + 1);                }            } else {                for (int i = fromPosition; i > toPosition; i--) {                    Collections.swap(mUserBookShelfResponses, i, i - 1);                }            }            mBookShelfAdapter.notifyItemMoved(fromPosition, toPosition);            //返回true表示执行拖动            return true;        }        @Override        public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {            //记录将要删除item的位置            int position = viewHolder.getAdapterPosition();            final UserBookShelfResponse bookShelfResponse = mUserBookShelfResponses.get(position);            bookShelfResponse.setIndex(position);            //将位置放到数据中，再保存到队列中方便操作            queue.add(bookShelfResponse);            //滑动删除，将该item数据从集合中移除，            //被移除的数据可能还需要被撤销，已经被保存到队列中了            mUserBookShelfResponses.remove(position);            mBookShelfAdapter.notifyItemRemoved(position);        }        //处理动画        @Override        public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {            if (actionState == ItemTouchHelper.ACTION_STATE_SWIPE) {                //滑动时改变Item的透明度，以实现滑动过程中实现渐变效果                final float alpha = 1 - Math.abs(dX) / (float) viewHolder.itemView.getWidth();                viewHolder.itemView.setAlpha(alpha);                viewHolder.itemView.setTranslationX(dX);            } else {                super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);            }        }        //滑动事件完成时回调        //在这里可以实现撤销操作        @Override        public void clearView(final RecyclerView recyclerView, final RecyclerView.ViewHolder viewHolder) {            super.clearView(recyclerView, viewHolder);            if (!queue.isEmpty()) {                //如果队列中有数据，说明刚才有删掉一些item                Snackbar.make(((BaseActivity) getActivity()).getToolbar(), R.string.delete_bookshelf_success, Snackbar.LENGTH_LONG).setAction(R.string.repeal, new View.OnClickListener() {                    @Override                    public void onClick(View v) {                    //SnackBar的撤销按钮被点击，队列中取出刚被删掉的数据，然后再添加到数据集合，实现数据被撤回的动作                        final UserBookShelfResponse bookShelfResponse = (UserBookShelfResponse) queue.remove();                    //通知Adapter                        mBookShelfAdapter.notifyItemInserted(bookShelfResponse.getIndex());                        mUserBookShelfResponses.add(bookShelfResponse.getIndex(), bookShelfResponse);                        //实际开发中遇到一个bug：删除第一个item再撤销出现的试图延迟                        //手动将recyclerView滑到顶部可以解决这个bug                        if (bookShelfResponse.getIndex() == 0) {                            mRecyclerView.smoothScrollToPosition(0);                        }                    }                }).setCallback(new Snackbar.Callback() {                //不撤销将做正在的删除操作，监听SnackBar消失事件，                //SnackBar消失（非排挤式消失）出队、访问服务器删除数据。                    @Override                    public void onDismissed(Snackbar snackbar, int event) {                        super.onDismissed(snackbar, event);                        //event 为消失原因，详细介绍在下文【附3】                        //排除一种情况就是联系删除多个item SnackBar挤掉前一个SnackBar导致的                        //消失                        if (event != DISMISS_EVENT_ACTION) {                            final UserBookShelfResponse bookShelfResponse = (UserBookShelfResponse) queue.remove();                            mLibraryPresenter.setBookShelf(BaseApplication.getUserId(), BaseApplication.getUserPassword(),                                    bookShelfResponse.getName(), bookShelfResponse.getRemark(), bookShelfResponse.getID(), 1);                        }                    }                }).show();            }        }        //是否长按进行拖拽        @Override        public boolean isLongPressDragEnabled() {            return true;        }    }

附1

/** * Author   :hymanme * Email    :hymanme@163.com * Create at 2016/1/12 * Description: */public class StaggeredGridDecoration extends RecyclerView.ItemDecoration {    private int left;    private int top;    private int right;    private int bottom;    public StaggeredGridDecoration(int left, int top, int right, int bottom) {        this.left = left;        this.top = top;        this.right = right;        this.bottom = bottom;    }    @Override    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {        outRect.bottom = bottom;        if (parent.getChildAdapterPosition(view) < 2) {            outRect.top = 2 * top;        } else {            outRect.top = top;        }        if (parent.getChildAdapterPosition(view) % 2 == 0) {            outRect.left = 2 * left;            outRect.right = right;        } else {            outRect.left = left;            outRect.right = 2 * right;        }    }}

附2

    class RecyclerViewScrollDetector extends RecyclerView.OnScrollListener {        //如果你的recyclerview是列表只需要用一个int就可以，private int lastVisibleItem;        //如果是gridview几列就需要几个数据的一个数组,        //如3列private int[] lastVisibleItem = {0, 0, 0};        private int[] lastVisibleItem = {0, 0};        private int mScrollThreshold = DensityUtils.dp2px(x.app(), 1);        @Override        public void onScrollStateChanged(RecyclerView recyclerView, int newState) {            super.onScrollStateChanged(recyclerView, newState);            if (newState == RecyclerView.SCROLL_STATE_IDLE &&                    (lastVisibleItem[0] + mLayoutManager.getSpanCount() >= mBookShelfAdapter.getItemCount())) {                onLoadMore();            }        }        @Override        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {            super.onScrolled(recyclerView, dx, dy);            boolean isSignificantDelta = Math.abs(dy) > mScrollThreshold;            if (isSignificantDelta) {                if (dy > 0) {                    ((MainActivity) getActivity()).hideFloatingBar();                } else {                    ((MainActivity) getActivity()).showFloatingBar();                }            }            lastVisibleItem = mLayoutManager.findLastCompletelyVisibleItemPositions(null);        }    }

附3

        /** Indicates that the Snackbar was dismissed via a swipe.*/        public static final int DISMISS_EVENT_SWIPE = 0;        /** Indicates that the Snackbar was dismissed via an action click.*/        public static final int DISMISS_EVENT_ACTION = 1;        /** Indicates that the Snackbar was dismissed via a timeout.*/        public static final int DISMISS_EVENT_TIMEOUT = 2;        /** Indicates that the Snackbar was dismissed via a call to {@link #dismiss()}.*/        public static final int DISMISS_EVENT_MANUAL = 3;        /** Indicates that the Snackbar was dismissed from a new Snackbar being shown.*/        public static final int DISMISS_EVENT_CONSECUTIVE = 4;

附4

//你还可以复写以下方法定义选中item时动画逻辑@Overridepublic void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {  super.onSelectedChanged(viewHolder, actionState);  //当选中Item时候会调用该方法，重写此方法可以实现选中时候的一些动画逻辑  Log.v("zxy","onSelectedChanged");}

总结
RecyclerView 是ListView的很好的替代品，它不仅带给我们更加方便地实现方法，还优化了视图复用效率。

参考：http://www.apkbus.com/android-246159-1-1.html?_dsign=46f0ee76

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