RecyclerView上下拖動條目排序，左右劃出屏幕刪除條目的最簡單的實現

效果圖

概述：

ItemTouchHelperAdapter：(★)

RecyclerListAdapter需要實現這個接口，
RecyclerListAdapter通過ItemTouchHelperAdapter的onItemMove和onItemDismiss方法來完成條目移動、條目消除的操作，並且通過notifyItemMoved()和notifyItemRemoved()來通知adapter數據的改變

ItemTouchHelperViewHolder：(★)

RecyclerListAdapter的內部類ItemViewHolder需要實現這個接口ItemViewHolder，通過調用ItemTouchHelperViewHolder的onItemSelected()和onItemClear()來完成條目被選中時（底色變灰色）、條目動畫完成時（底色變透明）的操作

SimpleItemTouchHelperCallback：(★★★★★)

該類繼承於抽象類ItemTouchHelper.Callback，ItemTouchHelper.Callback已經封裝了RecyclerView拖動、側滑的效果，我們只需要重寫其暴露出來的方法來控制拖拽即可，具體涉及到的方法有：（詳細介紹見源碼）
1. 構造函數
2. isLongPressDragEnabled()
3. isItemViewSwipeEnabled()
4. getMovementFlags()
5. onMove()
6. onSwiped()
7. onSelectedChanged()
8. clearView()

MainActivity/RecyclerListFragment(★)

外界如何調用

RecyclerListAdapter(★★★★★)

該類實現了ItemTouchHelperAdapter接口

RecyclerListAdapter通過ItemTouchHelperAdapter的onItemMove和onItemDismiss方法來完成條目移動、條目消除的操作，並且通過notifyItemMoved()和notifyItemRemoved()來通知adapter數據的改變

其內部類ItemViewHolder實現這個接口ItemTouchHelperViewHolder

通過調用ItemTouchHelperViewHolder的onItemSelected()和onItemClear()來完成條目被選中時（底色變灰色）、條目動畫完成時（底色變透明）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);
//         ★★★關鍵之處在於RecyclerListAdapter的寫法
        RecyclerListAdapter adapter = new RecyclerListAdapter();

        RecyclerView recyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
//        setHasFixedSize()方法用來使RecyclerView保持固定的大小，該信息被用於自身的優化。
        recyclerView.setHasFixedSize(true);
        recyclerView.setAdapter(adapter);
        recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));

        /**
         * ★★★★★★★★★★★★★★★★★★★★★★★
         * 要使用ItemTouchHelper，你需要創建一個ItemTouchHelper.Callback。
         * 這個接口可以讓你監聽“move(上下移動)”與 “swipe（左右滑動）”事件。這裡還是
         * ★控制view被選中
         * 的狀態以及★重寫默認動畫的地方。
         *
         * 如果你只是想要一個基本的實現，有一個
         * 幫助類可以使用：SimpleCallback,但是為了了解其工作機制，我們還是自己實現
         */
        ItemTouchHelper.Callback callback = new SimpleItemTouchHelperCallback(adapter);
        mItemTouchHelper = new ItemTouchHelper(callback);
//        將定義好的mItemTouchHelper應用於我們的recyclerView，使得recyclerView獲得move和swipe的效果
        mItemTouchHelper.attachToRecyclerView(recyclerView);


    }

}

SimpleItemTouchHelperCallback

<code class="hljs java">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.

 * 

 * Expects the <code>RecyclerView.Adapter</code> to react to {@link
 * ItemTouchHelperAdapter} callbacks and the <code>RecyclerView.ViewHolder</code> to implement
 * {@link ItemTouchHelperViewHolder}.
 *
 * 接下來的兩個是onMove()和onSwiped()，用於通知底層數據的更新。
 *
 * @author Paul Burke (ipaulpro)
 */
public class SimpleItemTouchHelperCallback extends ItemTouchHelper.Callback {

    private final ItemTouchHelperAdapter mAdapter;

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

    /**
     * 要支持長按RecyclerView item進入拖動操作，
     * 你必須在isLongPressDragEnabled()方法中返回true。
     * 或者，也可以調用ItemTouchHelper.startDrag(RecyclerView.ViewHolder)
     * 方法來開始一個拖動。
     */
    @Override
    public boolean isLongPressDragEnabled() {

        return true;//返回true表示支持長按開始拖拽
    }

    /**
     * 而要在view任意位置觸摸事件發生時啟用滑動操作，
     * 則直接在sItemViewSwipeEnabled()中返回true就可以了。
     * 或者，你也主動調用ItemTouchHelper.startSwipe(RecyclerView.ViewHolder)
     * 來開始滑動操作。
     */
    @Override
    public boolean isItemViewSwipeEnabled() {

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

    /**
     * ItemTouchHelper可以讓你輕易得到一個事件的方向。
     * 你需要重寫getMovementFlags()方法來指定可以支持
     * 的拖放和滑動的方向。
     * 使用helperItemTouchHelper.makeMovementFlags(int, int)
     * 來構造返回的flag。這裡我們啟用了上下左右兩種方向。
     * 注：上下為拖動（drag），左右為滑動（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動
//        return makeMovementFlags(dragFlags, 0);//第二項為0，表示你支持拖拽，不支持左右滑動
    }

  </code>
    /**
     * Called when ItemTouchHelper wants to move the dragged item from its old position to
     * the new position.
     * 當移動一個條目時被調用
     * <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()}).
     * 如果該方法返回true，認定條目已經移動到了新的位置
     * <p>
     * If you don‘t support drag & drop, this method will never be called.
     * 如果你不支持拖拽，此方法不會被調用
     *
     * @param recyclerView The RecyclerView to which ItemTouchHelper is attached to.
     *                     ItemTouchHelper所附著的RecyclerView
     * @param source   The ViewHolder which is being dragged by the user.
     *                 正在被用戶拖拽的位置
     * @param target       The ViewHolder over which the currently active item is being
     *                     dragged.
     *                     當前正在被拖拽的條目所經過的位置
     * @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.
     * 當被左右滑動時，調用該方法
     * 注意：這裡的ViewHolder統一翻譯成條目，通過ViewHolder可以得到關於條目的所有屬性（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.
     * 當你返回一個相對方向時（由getMovementFlags()所返回的方向），該方法使用的是相對方向，否則使用絕對方向
     * <p>
     * If you don‘t support swiping, this method will never be called.
     * 如果你不支持左右滑動，該方法不會被調用
     * <p>
     * ItemTouchHelper will keep a reference to the View until it is detached from
     * RecyclerView.
     * ItemTouchHelper將會持有View的引用，直到ItemTouchHelper不再附著在RecyclerView上時
     * As soon as it is detached, ItemTouchHelper will call
     * {@link #clearView(RecyclerView, RecyclerView.ViewHolder)}.
     * 當不再附著時，ItemTouchHelper會調用clearView方法
     *
     * @param viewHolder The ViewHolder which has been swiped by the user.
     *                   用戶拖拽的條目
     * @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}).
     *                   條目被左右滑動的方向，他是上、下、左、右中的一個，如果getMovementFlags返回了
     *                   相對標志flags代替了左、右方向，將使用這個返回的方向
     *
     */
    @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.
     * 當條目被改變（拖拽、側滑）時，該方法被調用
     * <p/>
     * If you override this method, you should call super.
     * 如果你重寫該方法，你應該調用super
     *
     * @param viewHolder  The new ViewHolder that is being swiped or dragged. Might be null if
     *                    it is cleared.
     *                    正在被拖拽/側滑的條目，可能為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}.
     *                    活動狀態：空閒、側滑、拖拽，根據這個判斷不同狀態下的操作
     *
     * @see #clearView(RecyclerView, RecyclerView.ViewHolder)
     */
    @Override
    public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
        if (actionState != ItemTouchHelper.ACTION_STATE_IDLE) {//只要這個條目不是空閒狀態（即：拖拽或者側滑）
            ItemTouchHelperViewHolder itemViewHolder = (ItemTouchHelperViewHolder) viewHolder;
            itemViewHolder.onItemSelected();//這裡改變選中時的條目的狀態
        }

        super.onSelectedChanged(viewHolder, actionState);
    }
    /**
     * Called by the ItemTouchHelper when the user interaction with an element is over and it
     * also completed its animation.
     * 當ItemTouchHelper已經完成他的動畫時（即用戶與條目交互完成後），該方法被調用
     * <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)}.
     * 這是一個很好的地方，用來清除所有條目動畫完成後的效果（可能你在onSelectedChanged()、onChildDraw()
     * onChildDrawOver()時賦予了條目很多效果，在這個方法裡，統統把這些效果清除掉）
     *
     * @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();//在這裡處理清除掉條目效果
    }
}

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.
     *
     *當一個條目被拖拽移動時，該方法將被調用，當條目被移動時，該方法都會被調用，而不是在拖拽結尾才被調用
     *
     * @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.
     *
     * 當左右滑動條目時，調用該方法
     *
     * @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.
     * 當ItemTouchHelper將拖拽/側滑注冊（作用）到條目上時，實現該方法去更新這個條目的視圖效果，
     * 以暗示該條目正在被操作
     *
     */
    void onItemSelected();


    /**
     * Called when the {@link ItemTouchHelper} has completed the move or swipe, and the active item
     * state should be cleared.
     * 當ItemTouchHelper完成了拖拽/側滑時，激活的條目效果應該被消除
     */
    void onItemClear();
}

主要的代碼：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要實現ItemTouchHelperAdapter
 *    重寫onItemDismiss（刪除條目）和onItemMove（移動條目）
 *
 * ★ RecyclerView.ViewHolder實現ItemTouchHelperViewHolder
 *    重寫onItemSelected（條目被選中時）和onItemClear（條目被拖拽之後）
 */
public class RecyclerListAdapter extends RecyclerView.Adapter
        implements ItemTouchHelperAdapter {

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

    private final List 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));
    }

//   當條目被刪除時的操作（實現ItemTouchHelperAdapter重寫onItemDismiss方法）
    @Override
    public void onItemDismiss(int position) {
        mItems.remove(position);
//        通知條目已經被刪除，與adapter互動
        notifyItemRemoved(position);
    }

    //   當條目被移動時的操作（實現ItemTouchHelperAdapter重寫onItemMove方法）
    @Override
    public void onItemMove(int fromPosition, int toPosition) {
//        ★移動一個條目分兩步：首先把該條目先移除，再考慮在對應要移動到的地方增加這個條目
        String prev = mItems.remove(fromPosition);
//        toPosition > fromPosition ? toPosition - 1 : toPosition,
//        即將拖動到的位置是否比開始拖動的位置大，
//        如果大，則在集合裡在toPosition - 1處填寫該條目，否則在toPosition處添加該條目
        mItems.add(toPosition > fromPosition ? toPosition - 1 : toPosition, prev);
//        通知條目被移動，與adapter互動
        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() {
//            當選中時，背景色為灰色
            itemView.setBackgroundColor(Color.LTGRAY);
        }

        @Override
        public void onItemClear() {
//            當拖拽完畢後，背景色為透明
            itemView.setBackgroundColor(0);
        }
    }
}

完整源碼：

AndroidStudy2015/ItemTouchHelperdemo">github