RecyclerView - 拖拽和移动项目到另一个项目上。

Question

我有一个适配器(Adapter)，RecyclerView和ItemTouchHelper。 我想创建占位符，以便在移动的结果中可以放置项目。 占位符现在是空元素。但我不知道如何直接将元素放在这个占位符上。

我的适配器：

public class DateTimeAdapter extends RecyclerView.Adapter<MainHolder> implements ItemTouchHelperAdapter {
    private List<MainItem> values;
    private RecyclerView.RecycledViewPool viewPool = new RecyclerView.RecycledViewPool();
    private Activity context;
    private final OnStartDragListener mDragStartListener;
    private boolean initEmpty = false;

    public DateTimeAdapter(Activity context, List<MainItem> values, OnStartDragListener dragListener) {
        this.values = values;
        this.context = context;
        mDragStartListener = dragListener;
    }


    @NonNull
    @Override
    public MainHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view;
        switch (viewType){
            case (Constants.ITEM_HEADER_TEXT_VIEWTYPE):
                view = LayoutInflater.from(context).inflate(R.layout.list_group_item, parent, false);
                return new HeaderHolder(view);
            case (Constants.ITEM_EVENT_TEXT_VIEWTYPE):
                view = LayoutInflater.from(context).inflate(R.layout.item_wo_items, parent, false);
                return new ItemHolder(view);
            case (Constants.ITEM_PLACEHOLDER_VIEWTYPE):
                view = LayoutInflater.from(context).inflate(R.layout.item_placeholder, parent, false);
                return new PlaceHolder(view);
            default: throw new IllegalArgumentException();
        }
    }

    @Override
    public void onBindViewHolder(@NonNull final MainHolder holder, int position) {
        holder.setData(values.get(position));

        if (holder.getItemViewType() == Constants.ITEM_PLACEHOLDER_VIEWTYPE){

        }
    }


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

    @Override
    public int getItemViewType(int position) {
        return values.get(position).getViewType();
    }

    protected LocalTime getStartTimebyHeader(int position){
        ListIterator<MainItem> listIterator = values.listIterator(position);
        while (listIterator.hasPrevious()){
            MainItem t = listIterator.previous();
            if (t.getHeaderItem() != null){
                DateTimeFormatter parse = new DateTimeFormatterBuilder().appendPattern("HH:mm").toFormatter();
                LocalTime localTime = LocalTime.parse(t.getHeaderItem().getHeaderText(), parse);
                return localTime;
            }
        }
        return null;
    }



    protected LocalTime getEndTimebyHeader(int position){
        ListIterator<MainItem> listIterator = values.listIterator(position);
        while (listIterator.hasNext()){
            MainItem t = listIterator.next();
            if (t.getHeaderItem() != null){
                DateTimeFormatter parse = new DateTimeFormatterBuilder().appendPattern("HH:mm").toFormatter();
                LocalTime localTime = LocalTime.parse(t.getHeaderItem().getHeaderText(), parse);
                return localTime;
            }
        }
        return null;
    }


    @Override
    public boolean onItemMove(int fromPosition, int toPosition) {
        if (fromPosition < toPosition) {
            for (int i = fromPosition; i < toPosition; i++) {
                Collections.swap(values, i, i + 1);
            }
        } else {
            for (int i = fromPosition; i > toPosition; i--) {
                Collections.swap(values, i, i - 1);
            }
        }
        notifyItemMoved(fromPosition, toPosition);

        return true;
    }

    @Override
    public void onItemDismiss(int position) {
        values.remove(position);
        notifyItemRemoved(position);
    }
}

我的ItemTouchHelper

 ItemTouchHelper.SimpleCallback simpleCallback = new ItemTouchHelper.SimpleCallback(0, 0) {


            @Override
            public boolean canDropOver(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder current, @NonNull RecyclerView.ViewHolder target) {
                if (target.getAdapterPosition() != 0 && target.getAdapterPosition() != dta.getItemCount()-1)
                    return true;
                return false;
            }

            @Override
            public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder target) {
                Log.d("onMove", Integer.toString(viewHolder.getAdapterPosition()) + " - " + Integer.toString(target.getAdapterPosition()));
                dta.onItemMove(viewHolder.getAdapterPosition(), target.getAdapterPosition());
                return true;

            }

            @Override
            public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int direction) {

            }

            @Override
            public int getMovementFlags(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder) {
                int dragFlags =  viewHolder.getItemViewType() == Constants.ITEM_EVENT_TEXT_VIEWTYPE ? ItemTouchHelper.UP | ItemTouchHelper.DOWN : 0;
                int swipeFlags =  viewHolder.getItemViewType() == Constants.ITEM_EVENT_TEXT_VIEWTYPE ? ItemTouchHelper.START | ItemTouchHelper.END : 0;
                return makeMovementFlags(dragFlags, swipeFlags);
            }

            @Override
            public void clearView(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder) {
                showingDatas.get(viewHolder.getAdapterPosition()).getEventItem().setTimeS(dta.getStartTimebyHeader(viewHolder.getAdapterPosition()));
                showingDatas.get(viewHolder.getAdapterPosition()).getEventItem().setTimeE(dta.getEndTimebyHeader(viewHolder.getAdapterPosition()));
                dta.notifyItemChanged(viewHolder.getAdapterPosition());
                super.clearView(recyclerView, viewHolder);
            }
        };

        ItemTouchHelper itemTouchHelper = new ItemTouchHelper(simpleCallback);
        itemTouchHelper.attachToRecyclerView(rvPlan);

我该怎么做？

- Кирилл Химов

Answer 1

问题已解决：使用数据类来区分普通视图和占位符视图。在适配器中使用以下列表：

data class MyData(var type:Int, var name: String)
val list = mutableListOf(MyData(0,"PlaceHolder"),MyData(1,"Normal"),MyData(1,"Noraml"),MyData(0,"Place Holder"),MyData(1,"Normal"),MyData(1,"Normal"))

自定义项目触摸监听器类：

    ItemTouchHelper(object : RecyclerViewDragDetector() {
        override fun onMove(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder, target: RecyclerView.ViewHolder): Boolean {

            if (adapter.getItemViewType(viewHolder.adapterPosition) == 1){
                if (adapter.getItemViewType(target.adapterPosition)!= 1){

                    list[target.adapterPosition].type = 1
                    list[target.adapterPosition].name = "Normal"
                    adapter.notifyItemChanged(target.adapterPosition)
                    list.removeAt(viewHolder.adapterPosition)
                    adapter.notifyDataSetChanged()
                }
            }
            return true
        }
        override fun isLongPressDragEnabled(): Boolean {
            return true
        }
    }).attachToRecyclerView(recyclerView)

根据您的需要更改适配器。我的示例适配器如下所示：

（请注意保留HTML标签）

    inner class MyAdapter: RecyclerView.Adapter<RecyclerView.ViewHolder>(){
    private val viewTypeHeader = 0
    private val viewTypeNormal = 1
    inner class MyHolder(view: View): RecyclerView.ViewHolder(view){
        val textView: TextView = view.findViewById(R.id.normal_tv)
        fun bind(myData: MyData){
            textView.text = myData.name
        }
    }
    inner class MyHeaderHolder(view:View): RecyclerView.ViewHolder(view){
        val textView: TextView = view.findViewById(R.id.header_tv)
        fun bind(myData: MyData){
            textView.text = myData.name
        }
    }
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
        return if (viewType == viewTypeHeader){
            val view = LayoutInflater.from(parent.context).inflate(R.layout.header, parent, false)
            MyHeaderHolder(view)
        }else {
            val view = LayoutInflater.from(parent.context).inflate(R.layout.list_item, parent, false)
            MyHolder(view)
        }
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
      if (getItemViewType(position) == viewTypeHeader){
            (holder as MyHeaderHolder).bind(list[position])
      }else{
          (holder as MyHolder).bind(list[position])
      }
    }

    override fun getItemViewType(position: Int): Int {
        return if (list[position].type == viewTypeHeader)
            return viewTypeHeader
        else
            viewTypeNormal

    }
    override fun getItemCount(): Int {
        return list.size
    }
}

- NRUSINGHA MOHARANA

---

这个解决方案不起作用。我想把EVENT ViewType的项目放在PLACEHOLDER ViewType的项目上。我该怎么做？ - Кирилл Химов

问题已经解决。您可以查看我的更新答案。 - NRUSINGHA MOHARANA

根据您的代码，占位符和项目只是在更改类型，对吗？ 但我想把一个项目放在一个占位符上。也就是说，占位符应该消失。并且在它的位置上出现一个项目。 也就是说，我拖放，指向占位符，松开手指，一个项目出现在占位符的位置。然后占位符被移除。 就像在Android屏幕上的图标一样-当您按住图标时，空框架出现在可以移动图标的位置。 - Кирилл Химов

哦，好的，那也可以。我会更新你的。 - NRUSINGHA MOHARANA

好的，我为您希望。 - Кирилл Химов