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
#直接上代码
//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Adapter
mBookShelfAdapter = 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) {
}
我们还会发现还有以下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 :[email protected]
* 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。原本用 listview 很难实现的功能用 RecyclerView 来实现，却变得很简单。吼吼。
