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
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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：
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