LinearLayoutManager prepareForDrop未被解雇

Question

我正在试图捕捉Recyclerview项在拖放操作(例如读取坐标)之后被删除时的点。

认为prepareForDrop事件的LinearLayoutManager将是正确的事情：

public class OverviewActivity extends AppCompatActivity implements OnStartDragListener {

private RecyclerView recyclerView;
private RecyclerAdapter myAdapter;
private LinearLayoutManager linearLayoutManager;
private ItemTouchHelper mItemTouchHelper;

private dbhelper db;

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

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
    linearLayoutManager = new LinearLayoutManager(this) {
        @Override
        public void prepareForDrop(View view, View target, int x, int y) {
            // do something
            return;
        }
    };
    recyclerView.setLayoutManager(linearLayoutManager);

    myAdapter = new RecyclerAdapter(this, this);
    recyclerView.setAdapter(myAdapter);
    myAdapter.setOnScrollToListener(new OnScrollToListener() {
        @Override
        public void scrollTo(int position) {
            recyclerView.scrollToPosition(position);
        }
    });

    ItemTouchHelper.Callback callback = new SimpleItemTouchHelperCallback(myAdapter);
    mItemTouchHelper = new ItemTouchHelper(callback);
    mItemTouchHelper.attachToRecyclerView(recyclerView);

    db = new dbhelper(this);
    db.open();

    myAdapter.addRootCards(3);
}
.......

创建LinearLayoutManager并将其附加到RecyclerView，并实现对prepareForDrop事件的重写。

问题是: prepareForDrop()从来没有被调用过，但是为什么，出了什么问题？

Answer 1

根据源代码，prepareForDrop()只有在LayoutManager instanceOf ViewDropHandler时才从onMoved调用。在你的情况下，是的。这使我相信onMoved()没有被调用。根据其javadocs，只有当onMoved()返回true时才调用onMove()。您还没有显示SimpleItemTouchHelperCallback的实现，但我猜它的onMove()实现返回false。