java - 为什么列表元素不交换？

Question

我有一个 RecyclerView 并实现了一个名为 onItemMove 的 onMove 命令。我正在使用 onItemMove 尝试让列表元素在拖动时交换位置，但列表元素只是悬停在每个元素上，它们不会交换。我该如何纠正这个问题？

注意 1:onItemDismiss 工作正常；它会将项目滑开并将其从列表中删除。

注意 2:我尝试过 Override onItemMove，但它实际上并没有覆盖它的父类(super class)。

列表适配器类:它包含 onItemMove 命令

public class ListAdapter extends RecyclerView.Adapter<ListAdapter.ListViewHolder> {
    private static final String TAG = "ListAdapter";
    Context context;
    private List<UserData> dataList = new ArrayList<>();
    LayoutInflater inflater;
    Listener listener;
    DbHelper dbHelper;



    public interface Listener {
        void nameToChnge(String name);
    }

    public ListAdapter(Context context, List<UserData> dataList1) {
        this.context = context;
        this.dataList = dataList1;
        this.listener= (Listener) context;
        inflater = LayoutInflater.from(context);
    }


    @Override
    public ListViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View convertView = inflater.inflate(R.layout.recylerview_one, parent, false);
        ListViewHolder viewHolder = new ListViewHolder(convertView);
        return viewHolder;
    }

    @Override
    public void onBindViewHolder(ListViewHolder holder, final int position) {
        holder.tv_name.setText(dataList.get(position).name);
        holder.tv_quantity.setText(dataList.get(position).quantity);
        holder.tv_description.setText(dataList.get(position).description + "");

        holder.relLayout.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                String s = dataList.get(position).id;
                Integer stringo = Integer.parseInt(s);
                Intent intent = new Intent(context, ItemEditActivity.class);
                intent.putExtra("ItemNumber", stringo);
                context.startActivity(intent);
            }
        });
    }

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

    class ListViewHolder extends RecyclerView.ViewHolder {
        TextView tv_name, tv_quantity, tv_description;
        RelativeLayout relLayout;


        public ListViewHolder(View itemView) {
            super(itemView);
            tv_name = (TextView) itemView.findViewById(R.id.nameDisplay);
            tv_quantity = (TextView) itemView.findViewById(R.id.quantityDisplay);
            tv_description = (TextView) itemView.findViewById(R.id.descriptionDisplay);
            relLayout = (RelativeLayout) itemView.findViewById(R.id.relLayout);
        }
    }



    public void onItemDismiss(final int position) {
        dataList.remove(position);
        notifyItemRemoved(position);

    }

    public void onItemMove(int fromPosition, int toPosition) {
        Collections.swap(dataList, fromPosition, toPosition);
        notifyItemMoved(fromPosition, toPosition);

    }
}

ItemTouchHelper 类:

  public class SimpleItemTouchHelperCallback extends ItemTouchHelper.Callback{
        private final ListAdapter  mAdapter;


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

        @Ov

erride
    public boolean isLongPressDragEnabled() {
        return true;
    }

    @Override
    public boolean isItemViewSwipeEnabled() {
        return true;
    }

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

    @Override
    public boolean onMove(RecyclerView recyclerView,
                          RecyclerView.ViewHolder viewHolder,
                          RecyclerView.ViewHolder target) {
        mAdapter.onItemMove(viewHolder.getAdapterPosition(), target.getAdapterPosition());

        return true;
    }

    @Override
    public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
        mAdapter.onItemDismiss(viewHolder.getAdapterPosition());
    }
}

我初始化 RecyclerView 和SimpleItemTouchHelperCallback:

public class MainActivity extends AppCompatActivity implements ListAdapter.Listener {
    private static final String TAG = "MainActivity";

    RecyclerView recyclerView;
    DbHelper dbHelper;
    ListAdapter adapter;
    FloatingActionButton fab;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        introItem();
        dbHelper = DbHelper.getInstance(getApplicationContext());

        recyclerView= (RecyclerView) findViewById(R.id.rv_contactlist);
        adapter = new ListAdapter(this, dbHelper.getAllUser());
        recyclerView.setAdapter(adapter);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));

        ItemTouchHelper.Callback callback =
                new SimpleItemTouchHelperCallback(adapter);
        ItemTouchHelper touchHelper = new ItemTouchHelper(callback);
        touchHelper.attachToRecyclerView(recyclerView);

        totalQuantity();

        adapter.notifyDataSetChanged();
        fabHideShow();
        versionCheckMethod();

    }

Answer 1

你只需要研究这个示例的代码并实现它:https://github.com/iPaulPro/Android-ItemTouchHelper-Demo/tree/master/app/src/main/java/co/paulburke/android/itemtouchhelperdemo

但基本上您需要的是创建两个接口(interface)。第一个:

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.
 *
 * @param fromPosition The start position of the moved item.
 * @param toPosition   Then end position of the moved item.

 */
void onItemMove(int fromPosition, int toPosition);


/**
 * Called when an item has been dismissed by a swipe.
 *
 * @param position The position of the item dismissed.

 */
void onItemDismiss(int position);
}

第二个:

public interface ItemTouchHelperViewHolder {
    /**
      * Implementations should update the item view to indicate it's active state.
     */
    void onItemSelected();


    /**
     * state should be cleared.
     */
    void onItemClear();
}

SimpleItemTouchHelperCallback 中的类似内容:

public class SimpleItemTouchHelperCallback extends ItemTouchHelper.Callback {

    private final ItemTouchHelperAdapter mAdapter;

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

    @Override
    public boolean isLongPressDragEnabled() {
        return true;
    }

    @Override
    public boolean isItemViewSwipeEnabled() {
        return false;
    }

    @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);
    }

    @Override
    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder source, RecyclerView.ViewHolder target) {
        mAdapter.onItemMove(source.getAdapterPosition(), target.getAdapterPosition());
        return true;
    }

    @Override
    public void onSwiped(RecyclerView.ViewHolder viewHolder, int i) {
        mAdapter.onItemDismiss(viewHolder.getAdapterPosition());
    }

    @Override
    public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
        if (actionState != ItemTouchHelper.ACTION_STATE_IDLE) {
            ItemTouchHelperViewHolder itemViewHolder = (ItemTouchHelperViewHolder) viewHolder;
            itemViewHolder.onItemSelected();
        }

        super.onSelectedChanged(viewHolder, actionState);
    }

    @Override
    public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        super.clearView(recyclerView, viewHolder);

        ItemTouchHelperViewHolder itemViewHolder = (ItemTouchHelperViewHolder) viewHolder;
        itemViewHolder.onItemClear();
    }
}

然后您必须更改 RecyclerViewAdapter，并在那里实现 onItemMove 方法，正如我们在其他注释中所说的那样。您还应该像这样实现 onStartDragListener:

    public interface OnStartDragListener {
    /**
     * Called when a view is requesting a start of a drag.
     *
     * @param viewHolder The holder of the view to drag.
     */
    void onStartDrag(RecyclerView.ViewHolder viewHolder);
}

然后在你的适配器 onBindViewHolder 中使用它(记得在类声明中实现所有接口(interface))像这样(你需要根据你的变量名更改这段代码):

holder.handleView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                if (MotionEventCompat.getActionMasked(event) == MotionEvent.ACTION_DOWN) {
                    mDragStartListener.onStartDrag(holder);
                }
                return false;
            }
        });

其中 mDragListener 是一个 OnStartDragListener 变量。

最后查看本指南了解更多信息:http://valokafor.com/remember-drag-and-drop-position-with-recyclerview/