ItemTouchHelper實現RecyclerView條目拖拽移動、滑動刪除

ItemTouchHelper

• 先來看看MainActivity onCreat()中的代碼
  我們需要用到ItemTouchHelper,在new的時候發現他需要一個callback 而我們就要在這個callback中做文章。

rvContent.setLayoutManager(new LinearLayoutManager(this));
        MyAdapter adapter = new MyAdapter(list, this);
        rvContent.setAdapter(adapter);
        MyItemTouchHelperCallback callback = new MyItemTouchHelperCallback(adapter);
        itemTouchHelper = new ItemTouchHelper(callback);
        itemTouchHelper.attachToRecyclerView(rvContent);

ItemTouchHelper.Callback

定義一個類 MyItemTouchHelperCallback extends ItemTouchHelper.Callback 重寫他的方法

• 獲取移動的方向 dragFlags是拖動的方向 swipeFlags是滑動的方向

    @Override
    public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;
        int swipeFlags = ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;
        return makeMovementFlags(dragFlags, swipeFlags);
    }

• 移動時的回調

public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder,
                          RecyclerView.ViewHolder target)

• 側滑時的回調

public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction)

• item選擇狀態發生改變

public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState)

• 實時繪製child的方法

public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder
            viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive)

• 刷新view防止 在重用view的時候出現錯位

public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder)

• 是否啓用長按拖拽

public boolean isLongPressDragEnabled()

看一下這個完整的類

public class MyItemTouchHelperCallback extends ItemTouchHelper.Callback {
    private ItemTouchMoveListener itemTouchMoveListener;
    public MyItemTouchHelperCallback(ItemTouchMoveListener itemTouchMoveListener) {
        this.itemTouchMoveListener=itemTouchMoveListener;
    }

    @Override
    public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;
        int swipeFlags = ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;
        return makeMovementFlags(dragFlags, swipeFlags);
    }

    @Override
    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder,
                          RecyclerView.ViewHolder target) {
        if(viewHolder.getItemViewType()!=viewHolder.getItemViewType()){
            return false;//不同條目類型不能移動
        }
        boolean result = itemTouchMoveListener.onItemMove(viewHolder.getAdapterPosition(), target
                .getAdapterPosition());
        return result;
    }

    /* 側滑時的回調*/
    @Override
    public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
        itemTouchMoveListener.onItemRemove(viewHolder.getAdapterPosition());
    }

    @Override
    public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
        super.onSelectedChanged(viewHolder, actionState);
        if (actionState != ItemTouchHelper.ACTION_STATE_IDLE) {
            viewHolder.itemView.setAlpha(0.5f);
        }
    }


    @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 percentage = 1-Math.abs(dX)/viewHolder.itemView.getWidth();
            viewHolder.itemView.setScaleX(percentage);
            viewHolder.itemView.setScaleY(percentage);
        }
        super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
    }

    @Override
    public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        viewHolder.itemView.setAlpha(1.0f);
        viewHolder.itemView.setScaleX(1.0f);
        viewHolder.itemView.setScaleY(1.0f);
        super.clearView(recyclerView, viewHolder);
    }

    /* 是否開啓長按拖動 */
    @Override
    public boolean isLongPressDragEnabled() {
        return true;
    }
}

ItemTouchMoveListener

• 可以看到，上一個類中用到了 ItemTouchMoveListener 這是幹什麼的呢？
• 我們先來看一下這個接口

public interface ItemTouchMoveListener {
    boolean onItemMove(int fromPosition, int toPosition);
    boolean onItemRemove(int position);
}

可以看到,接口中就兩個方法 onItemMove是item移動時交換的時候執行
onItemRemove是item移除的時候執行。
而這兩個動作都是adapter的方法，所以這裏讓adapter實現這個接口，在callback中適當的時候調用他們

notifyItemMoved(fromPosition, toPosition);
notifyItemRemoved(position);

MyAdapter

• 這裏再來看看recyclerview適配器 可以看到適配器實現了先前看到的那個ItemTouchMoveListener

class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> implements ItemTouchMoveListener{
    private List<String> list;
    private StartDragListener dragListener;


    public MyAdapter(List<String> list,StartDragListener dragListener) {
        super();
        this.list = list;
        this.dragListener = dragListener;
    }


    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.listitem, parent, false);
        return new ViewHolder(view);
    }
    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        holder.setData(holder,position);
    }

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

    class ViewHolder extends RecyclerView.ViewHolder {
        private TextView tvTitle;
        private ImageView ivIcon;

        public ViewHolder(View itemView) {
            super(itemView);
            initView(itemView);
        }

        private void initView(View itemView) {
            tvTitle = (TextView) itemView.findViewById(R.id.tv_title);
            ivIcon = (ImageView) itemView.findViewById(R.id.iv_icon);
        }
        void setData(final ViewHolder holder, int position) {
            tvTitle.setText(list.get(position));
            ivIcon.setOnTouchListener(new View.OnTouchListener() {
                @Override
                public boolean onTouch(View v, MotionEvent event) {
                    if(event.getAction()==MotionEvent.ACTION_DOWN){
                        dragListener.onStartDrag(holder);
                    }
                    return false;
                }
            });
        }
    }

    @Override
    public boolean onItemMove(int fromPosition, int toPosition) {
        Collections.swap(list,fromPosition,toPosition);//交換數據
        notifyItemMoved(fromPosition, toPosition);
        return true;
    }

    @Override
    public boolean onItemRemove(int position) {
        list.remove(position);
        notifyItemRemoved(position);
        return true;
    }
}

StartDragListener

• 在適配器中，我們用到了StartDragListener，並在ivIcon上添加了OnTouchListener，使得我們在觸摸時調用相應的方法。
• 調用什麼方法才能使條目拖動呢。我們發現ItemTouchHelper下有個startDrag方法。所以就需要在主函數中實現StartDragListener接口。並且在主函數中實現響應的方法。

public interface StartDragListener {
    public void onStartDrag(ViewHolder viewHolder);
}

MainActivity

• 主函數就沒什麼說的了

public class MainActivity extends AppCompatActivity implements StartDragListener{
    private RecyclerView rvContent;
    private ItemTouchHelper itemTouchHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
        List<String> list = new ArrayList<>();
        for (int i = 0; i < 20; i++) {
            list.add("第" + i + "條數據");
        }

        rvContent.setLayoutManager(new LinearLayoutManager(this));
        MyAdapter adapter = new MyAdapter(list, this);
        rvContent.setAdapter(adapter);
        MyItemTouchHelperCallback callback = new MyItemTouchHelperCallback(adapter);
        itemTouchHelper = new ItemTouchHelper(callback);
        itemTouchHelper.attachToRecyclerView(rvContent);
    }

    private void initView() {
        rvContent = (RecyclerView) findViewById(R.id.rv_content);
    }

    @Override
    public void onStartDrag(RecyclerView.ViewHolder viewHolder) {
        itemTouchHelper.startDrag(viewHolder);
    }
}