RecyclerView上下拖动条目排序，左右划出屏幕删除条目的最简单的实现

效果图

参考

RecyclerView的拖动和滑动 第一部分 ：基本的ItemTouchHelper示例

概述：

ItemTouchHelperAdapter：(★)

RecyclerListAdapter需要实现这个接口，
RecyclerListAdapter通过ItemTouchHelperAdapter的onItemMove和onItemDismiss方法来完成条目移动、条目消除的操作，并且通过notifyItemMoved()和notifyItemRemoved()来通知adapter数据的改变

ItemTouchHelperViewHolder：(★)

RecyclerListAdapter的内部类ItemViewHolder需要实现这个接口ItemViewHolder，通过调用ItemTouchHelperViewHolder的onItemSelected()和onItemClear()来完成条目被选中时（底色变灰色）、条目动画完成时（底色变透明）的操作

SimpleItemTouchHelperCallback：(★★★★★)

该类继承于抽象类ItemTouchHelper.Callback，ItemTouchHelper.Callback已经封装了RecyclerView拖动、侧滑的效果，我们只需要重写其暴露出来的方法来控制拖拽即可，具体涉及到的方法有：（详细介绍见源码）
1. 构造函数
2. isLongPressDragEnabled()
3. isItemViewSwipeEnabled()
4. getMovementFlags()
5. onMove()
6. onSwiped()
7. onSelectedChanged()
8. clearView()

MainActivity/RecyclerListFragment(★)

外界如何调用

RecyclerListAdapter(★★★★★)

• 该类实现了ItemTouchHelperAdapter接口

  RecyclerListAdapter通过ItemTouchHelperAdapter的onItemMove和onItemDismiss方法来完成条目移动、条目消除的操作，并且通过notifyItemMoved()和notifyItemRemoved()来通知adapter数据的改变

• 其内部类ItemViewHolder实现这个接口ItemTouchHelperViewHolder

通过调用ItemTouchHelperViewHolder的onItemSelected()和onItemClear()来完成条目被选中时（底色变灰色）、条目动画完成时（底色变透明）的操作

外部使用Activity/Fragment

package co.paulburke.android.itemtouchhelperdemo;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.helper.ItemTouchHelper;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import co.paulburke.android.itemtouchhelperdemo.helper.SimpleItemTouchHelperCallback;

/**
 * @author Paul Burke (ipaulpro)
 */
public class RecyclerListFragment extends Fragment {

    private ItemTouchHelper mItemTouchHelper;

    public RecyclerListFragment() {
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_main, container, false);
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
//         ★★★关键之处在于RecyclerListAdapter的写法
        RecyclerListAdapter adapter = new RecyclerListAdapter();

        RecyclerView recyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
//        setHasFixedSize()方法用来使RecyclerView保持固定的大小，该信息被用于自身的优化。
        recyclerView.setHasFixedSize(true);
        recyclerView.setAdapter(adapter);
        recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));

        /**
         * ★★★★★★★★★★★★★★★★★★★★★★★
         * 要使用ItemTouchHelper，你需要创建一个ItemTouchHelper.Callback。
         * 这个接口可以让你监听“move(上下移动)”与 “swipe（左右滑动）”事件。这里还是
         * ★控制view被选中
         * 的状态以及★重写默认动画的地方。
         *
         * 如果你只是想要一个基本的实现，有一个
         * 帮助类可以使用：SimpleCallback,但是为了了解其工作机制，我们还是自己实现
         */
        ItemTouchHelper.Callback callback = new SimpleItemTouchHelperCallback(adapter);
        mItemTouchHelper = new ItemTouchHelper(callback);
//        将定义好的mItemTouchHelper应用于我们的recyclerView，使得recyclerView获得move和swipe的效果
        mItemTouchHelper.attachToRecyclerView(recyclerView);


    }

}

SimpleItemTouchHelperCallback

package co.paulburke.android.itemtouchhelperdemo.helper;

import android.graphics.Canvas;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.helper.ItemTouchHelper;

/**
 * An implementation of {@link ItemTouchHelper.Callback} that enables basic drag & drop and
 * swipe-to-dismiss. Drag events are automatically started by an item long-press.<br/>
 * </br/>
 * Expects the <code>RecyclerView.Adapter</code> to react to {@link
 * ItemTouchHelperAdapter} callbacks and the <code>RecyclerView.ViewHolder</code> to implement
 * {@link ItemTouchHelperViewHolder}.
 *
 * 接下来的两个是onMove()和onSwiped()，用于通知底层数据的更新。
 *
 * @author Paul Burke (ipaulpro)
 */
public class SimpleItemTouchHelperCallback extends ItemTouchHelper.Callback {

    private final ItemTouchHelperAdapter mAdapter;

    public SimpleItemTouchHelperCallback(ItemTouchHelperAdapter adapter) {
        mAdapter = adapter;
    }

    /**
     * 要支持长按RecyclerView item进入拖动操作，
     * 你必须在isLongPressDragEnabled()方法中返回true。
     * 或者，也可以调用ItemTouchHelper.startDrag(RecyclerView.ViewHolder)
     * 方法来开始一个拖动。
     */
    @Override
    public boolean isLongPressDragEnabled() {

        return true;//返回true表示支持长按开始拖拽
    }

    /**
     * 而要在view任意位置触摸事件发生时启用滑动操作，
     * 则直接在sItemViewSwipeEnabled()中返回true就可以了。
     * 或者，你也主动调用ItemTouchHelper.startSwipe(RecyclerView.ViewHolder)
     * 来开始滑动操作。
     */
    @Override
    public boolean isItemViewSwipeEnabled() {

        return true;//返回true表示支持左右滑动
    }

    /**
     * ItemTouchHelper可以让你轻易得到一个事件的方向。
     * 你需要重写getMovementFlags()方法来指定可以支持
     * 的拖放和滑动的方向。
     * 使用helperItemTouchHelper.makeMovementFlags(int, int)
     * 来构造返回的flag。这里我们启用了上下左右两种方向。
     * 注：上下为拖动（drag），左右为滑动（swipe）。
     */
    @Override
    public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        final int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;
        final int swipeFlags = ItemTouchHelper.START | ItemTouchHelper.END;
        return makeMovementFlags(dragFlags, swipeFlags);//表示支持上下拖拽和左右滑动
//        return makeMovementFlags(dragFlags, 0);//第二项为0，表示你支持拖拽，不支持左右滑动
    }

    /**
     * Called when ItemTouchHelper wants to move the dragged item from its old position to
     * the new position.
     * 当移动一个条目时被调用
     * <p>
     * If this method returns true, ItemTouchHelper assumes {@code viewHolder} has been moved
     * to the adapter position of {@code target} ViewHolder
     * ({@link RecyclerView.ViewHolder#getAdapterPosition()
     * ViewHolder#getAdapterPosition()}).
     * 如果该方法返回true，认定条目已经移动到了新的位置
     * <p>
     * If you don‘t support drag & drop, this method will never be called.
     * 如果你不支持拖拽，此方法不会被调用
     *
     * @param recyclerView The RecyclerView to which ItemTouchHelper is attached to.
     *                     ItemTouchHelper所附着的RecyclerView
     * @param source   The ViewHolder which is being dragged by the user.
     *                 正在被用户拖拽的位置
     * @param target       The ViewHolder over which the currently active item is being
     *                     dragged.
     *                     当前正在被拖拽的条目所经过的位置
     * @return True if the {@code viewHolder} has been moved to the adapter position of
     * {@code target}.
     * @see #onMoved(RecyclerView, RecyclerView.ViewHolder, int, RecyclerView.ViewHolder, int, int, int)
     */


    @Override
    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder source, RecyclerView.ViewHolder target) {
        mAdapter.onItemMove(source.getAdapterPosition(), target.getAdapterPosition());
        return true;
    }
    /**
     * Called when a ViewHolder is swiped by the user.
     * 当被左右滑动时，调用该方法
     * 注意：这里的ViewHolder统一翻译成条目，通过ViewHolder可以得到关于条目的所有属性（如：位置等等）
     * <p>
     * If you are returning relative directions ( {START} , {END}) from the
     * {@link #getMovementFlags(RecyclerView, RecyclerView.ViewHolder)} method, this method
     * will also use relative directions. Otherwise, it will use absolute directions.
     * 当你返回一个相对方向时（由getMovementFlags()所返回的方向），该方法使用的是相对方向，否则使用绝对方向
     * <p>
     * If you don‘t support swiping, this method will never be called.
     * 如果你不支持左右滑动，该方法不会被调用
     * <p>
     * ItemTouchHelper will keep a reference to the View until it is detached from
     * RecyclerView.
     * ItemTouchHelper将会持有View的引用，直到ItemTouchHelper不再附着在RecyclerView上时
     * As soon as it is detached, ItemTouchHelper will call
     * {@link #clearView(RecyclerView, RecyclerView.ViewHolder)}.
     * 当不再附着时，ItemTouchHelper会调用clearView方法
     *
     * @param viewHolder The ViewHolder which has been swiped by the user.
     *                   用户拖拽的条目
     * @param direction  The direction to which the ViewHolder is swiped. It is one of
     *                   {UP}, {DOWN},
     *                   {LEFT} or {RIGHT}. If your
     *                   {@link #getMovementFlags(RecyclerView, RecyclerView.ViewHolder)}
     *                   method
     *                   returned relative flags instead of {LEFT} / {RIGHT};
     *                   `direction` will be relative as well. ({START} or {
     *                   END}).
     *                   条目被左右滑动的方向，他是上、下、左、右中的一个，如果getMovementFlags返回了
     *                   相对标志flags代替了左、右方向，将使用这个返回的方向
     *
     */
    @Override
    public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
        mAdapter.onItemDismiss(viewHolder.getAdapterPosition());
    }
    /**
     * Called when the ViewHolder swiped or dragged by the ItemTouchHelper is changed.
     * 当条目被改变（拖拽、侧滑）时，该方法被调用
     * <p/>
     * If you override this method, you should call super.
     * 如果你重写该方法，你应该调用super
     *
     * @param viewHolder  The new ViewHolder that is being swiped or dragged. Might be null if
     *                    it is cleared.
     *                    正在被拖拽/侧滑的条目，可能为null，如果他被清除掉
     * @param actionState One of {@link ItemTouchHelper#ACTION_STATE_IDLE},
     *                    {@link ItemTouchHelper#ACTION_STATE_SWIPE} or
     *                    {@link ItemTouchHelper#ACTION_STATE_DRAG}.
     *                    活动状态：空闲、侧滑、拖拽，根据这个判断不同状态下的操作
     *
     * @see #clearView(RecyclerView, RecyclerView.ViewHolder)
     */
    @Override
    public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
        if (actionState != ItemTouchHelper.ACTION_STATE_IDLE) {//只要这个条目不是空闲状态（即：拖拽或者侧滑）
            ItemTouchHelperViewHolder itemViewHolder = (ItemTouchHelperViewHolder) viewHolder;
            itemViewHolder.onItemSelected();//这里改变选中时的条目的状态
        }

        super.onSelectedChanged(viewHolder, actionState);
    }
    /**
     * Called by the ItemTouchHelper when the user interaction with an element is over and it
     * also completed its animation.
     * 当ItemTouchHelper已经完成他的动画时（即用户与条目交互完成后），该方法被调用
     * <p>
     * This is a good place to clear all changes on the View that was done in
     * {@link #onSelectedChanged(RecyclerView.ViewHolder, int)},
     * {@link #onChildDraw(Canvas, RecyclerView, RecyclerView.ViewHolder, float, float, int,
     * boolean)} or
     * {@link #onChildDrawOver(Canvas, RecyclerView, RecyclerView.ViewHolder, float, float, int, boolean)}.
     * 这是一个很好的地方，用来清除所有条目动画完成后的效果（可能你在onSelectedChanged()、onChildDraw()
     * onChildDrawOver()时赋予了条目很多效果，在这个方法里，统统把这些效果清除掉）
     *
     * @param recyclerView The RecyclerView which is controlled by the ItemTouchHelper.
     * @param viewHolder   The View that was interacted by the user.
     */
    @Override
    public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        super.clearView(recyclerView, viewHolder);

        ItemTouchHelperViewHolder itemViewHolder = (ItemTouchHelperViewHolder) viewHolder;
        itemViewHolder.onItemClear();//在这里处理清除掉条目效果
    }
}

ItemTouchHelperAdapter

package co.paulburke.android.itemtouchhelperdemo.helper;

import android.support.v7.widget.RecyclerView;

/**
 * Interface to notify a {@link RecyclerView.Adapter} of moving and dismissal event from a {@link
 * android.support.v7.widget.helper.ItemTouchHelper.Callback}.
 *
 * @author Paul Burke (ipaulpro)
 */
public interface ItemTouchHelperAdapter {

    /**
     * Called when an item has been dragged far enough to trigger a move. This is called every time
     * an item is shifted, and not at the end of a "drop" event.
     *
     *当一个条目被拖拽移动时，该方法将被调用，当条目被移动时，该方法都会被调用，而不是在拖拽结尾才被调用
     *
     * @param fromPosition The start position of the moved item.
     * @param toPosition   Then end position of the moved item.
     * @see RecyclerView#getAdapterPositionFor(RecyclerView.ViewHolder)
     * @see RecyclerView.ViewHolder#getAdapterPosition()
     */

    void onItemMove(int fromPosition, int toPosition);


    /**
     * Called when an item has been dismissed by a swipe.
     *
     * 当左右滑动条目时，调用该方法
     *
     * @param position The position of the item dismissed.
     * @see RecyclerView#getAdapterPositionFor(RecyclerView.ViewHolder)
     * @see RecyclerView.ViewHolder#getAdapterPosition()
     */
    void onItemDismiss(int position);
}

ItemTouchHelperViewHolder

package co.paulburke.android.itemtouchhelperdemo.helper;

import android.support.v7.widget.helper.ItemTouchHelper;

/**
 * Interface to notify an item ViewHolder of relevant callbacks from {@link
 * android.support.v7.widget.helper.ItemTouchHelper.Callback}.
 *
 * @author Paul Burke (ipaulpro)
 */
public interface ItemTouchHelperViewHolder {

    /**
     * Called when the {@link ItemTouchHelper} first registers an item as being moved or swiped.
     * Implementations should update the item view to indicate it‘s active state.
     * 当ItemTouchHelper将拖拽/侧滑注册（作用）到条目上时，实现该方法去更新这个条目的视图效果，
     * 以暗示该条目正在被操作
     *
     */
    void onItemSelected();


    /**
     * Called when the {@link ItemTouchHelper} has completed the move or swipe, and the active item
     * state should be cleared.
     * 当ItemTouchHelper完成了拖拽/侧滑时，激活的条目效果应该被消除
     */
    void onItemClear();
}

主要的代码：RecyclerListAdapter

package co.paulburke.android.itemtouchhelperdemo;

import android.graphics.Color;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import co.paulburke.android.itemtouchhelperdemo.helper.ItemTouchHelperAdapter;
import co.paulburke.android.itemtouchhelperdemo.helper.ItemTouchHelperViewHolder;

/**
 * @author Paul Burke (ipaulpro)
 * ★ RecyclerListAdapter要实现ItemTouchHelperAdapter
 *    重写onItemDismiss（删除条目）和onItemMove（移动条目）
 *
 * ★ RecyclerView.ViewHolder实现ItemTouchHelperViewHolder
 *    重写onItemSelected（条目被选中时）和onItemClear（条目被拖拽之后）
 */
public class RecyclerListAdapter extends RecyclerView.Adapter<RecyclerListAdapter.ItemViewHolder>
        implements ItemTouchHelperAdapter {

    private static final String[] STRINGS = new String[]{
            "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten"
    };

    private final List<String> mItems = new ArrayList<>();

    public RecyclerListAdapter() {
        mItems.addAll(Arrays.asList(STRINGS));
    }

    @Override
    public ItemViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_main, parent, false);
        ItemViewHolder itemViewHolder = new ItemViewHolder(view);
        return itemViewHolder;
    }

    @Override
    public void onBindViewHolder(final ItemViewHolder holder, int position) {
        holder.textView.setText(mItems.get(position));
    }

//   当条目被删除时的操作（实现ItemTouchHelperAdapter重写onItemDismiss方法）
    @Override
    public void onItemDismiss(int position) {
        mItems.remove(position);
//        通知条目已经被删除，与adapter互动
        notifyItemRemoved(position);
    }

    //   当条目被移动时的操作（实现ItemTouchHelperAdapter重写onItemMove方法）
    @Override
    public void onItemMove(int fromPosition, int toPosition) {
//        ★移动一个条目分两步：首先把该条目先移除，再考虑在对应要移动到的地方增加这个条目
        String prev = mItems.remove(fromPosition);
//        toPosition > fromPosition ? toPosition - 1 : toPosition,
//        即将拖动到的位置是否比开始拖动的位置大，
//        如果大，则在集合里在toPosition - 1处填写该条目，否则在toPosition处添加该条目
        mItems.add(toPosition > fromPosition ? toPosition - 1 : toPosition, prev);
//        通知条目被移动，与adapter互动
        notifyItemMoved(fromPosition, toPosition);
    }

    @Override
    public int getItemCount() {
        return mItems.size();
    }

    public static class ItemViewHolder extends RecyclerView.ViewHolder implements
            ItemTouchHelperViewHolder {

        public final TextView textView;

        public ItemViewHolder(View itemView) {
            super(itemView);
            textView = (TextView) itemView;
        }

        @Override
        public void onItemSelected() {
//            当选中时，背景色为灰色
            itemView.setBackgroundColor(Color.LTGRAY);
        }

        @Override
        public void onItemClear() {
//            当拖拽完毕后，背景色为透明
            itemView.setBackgroundColor(0);
        }
    }
}

完整源码：

github