ItemTouchHelper类及RecyclerView的item滑动删除和拖拽案例

谁践踏了优雅 2022-08-22 05:53 198阅读 0赞

ItemTouchHelper类是v7包下的一个针对RecyclerView拖拽和滑动删除的辅助类，英文的解释：This is a utility class to add swipe to dismiss and drag & drop support to RecyclerView.

下面用一个例子介绍一下：

先看效果图：  
![这里写图片描述][20160525164914611]

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先介绍一下项目的结构图：  
![这里写图片描述][20160525164948539]

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简要说明

helper文件夹中，是自己定义的接口和类，ItemTouchHelperAdapter和ItemTouchHelperViewHolder是需要RecyclerView.Adapter和RecyclerView.ViewHolder的子类去实现的。SimpleItemTouchHelperCallback继承了ItemTouchHelper.Callback，在SimpleItemTouchHelperCallback需要实现3个方法，分别是getMovementFlags()，onMove()，onSwiped()。

ItemTouchHelper.Callback中的几个方法

*  getMovementFlags()：应该返回一个组合标志，它定义了在每个状态下启用的移动方向  
    原文解释：Should return a composite flag which defines the enabled move directions in each state(idle, swiping, dragging).
 *  onMove():当把之前的位置拖拽到新的位置上时调用  
    原文解释： Called when ItemTouchHelper wants to move the dragged item from its old position to the new position.
 *  onSwiped():当ViewHolder被用户滑动删除后调用。  
    原文解释：Called when a ViewHolder is swiped by the user.
    
    \-onChildDraw():在RecyclerView调用onDraw方法的时候，调用此方法  
    原文解释：Called by ItemTouchHelper on RecyclerView’s onDraw callback  
    可以在这个方法中，对itemView进行设置。如透明度，背景的变化等
 *  onSelectedChanged（）：当item’touViewHolder拖拽或滑动  
    原文解释：Called when the ViewHolder swiped or dragged by the ItemTouchHelper is changed.
 *  clearView（）：当用户与itemview交互完且动画执行完，调用  
    原文解释：Called by the ItemTouchHelper when the user interaction with an element is over and it also completed its animation.

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将RecyclerView依附到ItemTouchHelper中

ItemTouchHelper.Callback callback = new SimpleItemTouchHelperCallback(adapter);
    itemTouchHelper = new ItemTouchHelper(callback);
    itemTouchHelper.attachToRecyclerView(mRecyclerView);

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下面看具体代码：  
helper文件夹中：

ItemTouchHelperAdapter接口

public interface ItemTouchHelperAdapter {
        void onItemMove(int fromPosition , int toPosition);
        void onItemDelete(int position);
    }

ItemTouchHelperViewHolder接口

public interface ItemTouchHelperViewHolder {
        void onItemSelect();
        void onItemClear();
    }

SimpleItemTouchHelperCallback

public class SimpleItemTouchHelperCallback extends ItemTouchHelper.Callback { 
    
        private static final float ALPHA_NORMAL = 1.0f;
        private ItemTouchHelperAdapter mAdapter;
    
        public SimpleItemTouchHelperCallback(ItemTouchHelperAdapter adapter) {
            this.mAdapter = adapter;
        }
    
        @Override
        public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
    
            if (recyclerView.getLayoutManager() instanceof GridLayoutManager) {
                int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN | ItemTouchHelper.START | ItemTouchHelper.END;
                int swipeFlags = 0;
                return makeMovementFlags(dragFlags, swipeFlags);
            } else if (recyclerView.getLayoutManager() instanceof LinearLayoutManager) {
                int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;
                int swipeFlags = ItemTouchHelper.START | ItemTouchHelper.END;
                return makeMovementFlags(dragFlags, swipeFlags);
            }
            return 0;
        }
    
        @Override
        public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
    
            if (viewHolder.getItemViewType() != target.getItemViewType()) {
                return false;
            }
    
            mAdapter.onItemMove(viewHolder.getAdapterPosition(), target.getAdapterPosition());
    
            return true;
        }
    
        @Override
        public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
            mAdapter.onItemDelete(viewHolder.getAdapterPosition());
        }
    
        @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) {
                float alpha = ALPHA_NORMAL - Math.abs(dX) / viewHolder.itemView.getWidth();
                viewHolder.itemView.setAlpha(alpha);
                viewHolder.itemView.setTranslationX(dX);
            } else {
                super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
            }
    
        }
    
        @Override
        public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
    
            if (actionState != ItemTouchHelper.ACTION_STATE_IDLE) {
                if (viewHolder instanceof ItemTouchHelperViewHolder) {
                    ItemTouchHelperViewHolder itemTouchHelperViewHolder = (ItemTouchHelperViewHolder) viewHolder;
                    itemTouchHelperViewHolder.onItemSelect();
                }
            }
    
            super.onSelectedChanged(viewHolder, actionState);
        }
    
        @Override
        public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
            super.clearView(recyclerView, viewHolder);
    
            viewHolder.itemView.setAlpha(ALPHA_NORMAL);
    
            if (viewHolder instanceof ItemTouchHelperViewHolder) {
                ItemTouchHelperViewHolder itemTouchHelperViewHolder = (ItemTouchHelperViewHolder) viewHolder;
                itemTouchHelperViewHolder.onItemClear();
            }
        }
    }

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布局文件：

activity.xml

fragment.xml文件

recycler\_item文件：

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在MainActivity文件中：

public class MainActivity extends AppCompatActivity { 
    
        private FloatingActionButton fab;
        private boolean isList = true;
        private FragmentTransaction fragmentTransaction_list;
        private FragmentTransaction fragmentTransaction_grid;
        private ListFragment listFragment;
        private GridFragment gridFragment;
        private FrameLayout frameLayout_grid;
        private FrameLayout frameLayout_list;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            initView();
            initListener();
        }
    
        private void initView() {
            fab = (FloatingActionButton) findViewById(R.id.fab);
            frameLayout_list = (FrameLayout) findViewById(R.id.fragment_list);
            frameLayout_grid = (FrameLayout) findViewById(R.id.fragment_grid);
            listFragment = new ListFragment();
            gridFragment = new GridFragment();
            fragmentTransaction_list = getSupportFragmentManager().beginTransaction().replace(R.id.fragment_list, listFragment, "list");
            fragmentTransaction_list.commit();
            fragmentTransaction_grid = getSupportFragmentManager().beginTransaction().replace(R.id.fragment_grid, gridFragment, "grid");
            fragmentTransaction_grid.commit();
        }
    
        private void initListener() {
            fab.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    if (isList) {
                        frameLayout_list.setVisibility(View.GONE);
                        frameLayout_grid.setVisibility(View.VISIBLE);
                        fab.setImageResource(R.mipmap.grid);
                        isList = false;
                    } else {
                        frameLayout_list.setVisibility(View.VISIBLE);
                        frameLayout_grid.setVisibility(View.GONE);
                        fab.setImageResource(R.mipmap.list);
                        isList = true;
                    }
                }
            });
        }
    }

ListFragment文件

public class ListFragment extends Fragment { 
    
        private RecyclerView mRecyclerView;
        private RecyclerView.LayoutManager manager;
        private MyAdapter adapter;
        private ItemTouchHelper itemTouchHelper;
        private List<String> mdatas = new ArrayList<>();
    
        @Nullable
        @Override
        public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    
            View view = inflater.inflate(R.layout.fragment, container, false);
            return view;
        }
    
        @Override
        public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
            mRecyclerView = (RecyclerView) view.findViewById(R.id.recycler);
            manager = new LinearLayoutManager(getContext(), LinearLayoutManager.VERTICAL, false);
            initData();
            initRecycler();
        }
    
        private void initData() {
            for (int i = 0; i < 30; i++) {
                mdatas.add("这是第" + i + "item");
            }
        }
    
        private void initRecycler() {
    
            mRecyclerView.setLayoutManager(manager);
            mRecyclerView.setHasFixedSize(true);
            adapter = new MyAdapter(getContext(), mdatas);
            mRecyclerView.setAdapter(adapter);
    
            //RecyclerView与ItemTouchHelper关联
            ItemTouchHelper.Callback callback = new SimpleItemTouchHelperCallback(adapter);
            itemTouchHelper = new ItemTouchHelper(callback);
            itemTouchHelper.attachToRecyclerView(mRecyclerView);
        }
    }

GridFragment 文件与ListFragment基本相同，不相同的只有LayoutManager.

//初始化的时候换成GridLayoutManager对象
       manager = new GridLayoutManager(getContext(),2);

MyAdapter文件

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> implements ItemTouchHelperAdapter { 
    
        private Context mContext;
        private List<String> mDatas = new ArrayList<>();
    
        public MyAdapter(Context context, List<String> mdatas) {
            this.mContext = context;
            this.mDatas = mdatas;
        }
    
        @Override
        public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    
            View view = LayoutInflater.from(mContext).inflate(R.layout.recycler_item, parent, false);
    
            return new MyViewHolder(view);
        }
    
        @Override
        public void onBindViewHolder(MyViewHolder holder, int position) {
            holder.textView.setText(mDatas.get(position));
        }
    
        @Override
        public int getItemCount() {
            if (null == mDatas) {
                return 0;
            }
            return mDatas.size();
        }
    
        @Override
        public void onItemMove(int fromPosition, int toPosition) {
            Collections.swap(mDatas, fromPosition, toPosition);
            notifyItemMoved(fromPosition, toPosition);
        }
    
        @Override
        public void onItemDelete(int position) {
            mDatas.remove(position);
            notifyItemRemoved(position);
        }
    
        class MyViewHolder extends RecyclerView.ViewHolder implements ItemTouchHelperViewHolder { 
    
            TextView textView;
    
            public MyViewHolder(View itemView) {
                super(itemView);
                initView();
                initListener();
            }
    
            private void initView() {
                textView = (TextView) itemView.findViewById(R.id.recycler_tv);
            }
    
            private void initListener() {
                //事件监听
            }
    
            @Override
            public void onItemSelect() {
                itemView.setBackgroundColor(Color.LTGRAY);
            }
    
            @Override
            public void onItemClear() {
                itemView.setBackgroundColor(0);
            }
        }
    }

[20160525164914611]: /images/20220722/9ab3f60538e344ef88ad4899decae39e.png
[20160525164948539]: /images/20220722/e84247b97bc84d33b7739b19e87e07f7.png