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我试图在拖放操作后Recyclerview删除项目时抓住点，例如读出坐标。

认为该prepareForDrop事件LinearLayoutManager是正确的：

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 prepareForDrop 事件的 Override。

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

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1 回答 1

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根据源代码 prepareForDrop() 仅在 LayoutManager instanceOf ViewDropHandler 时从 onMoved 调用。在你的情况下，它是。这让我相信 onMoved() 没有被调用。根据其 javadocs onMove() 仅在 onMove() 返回 true 时调用。您还没有展示 SimpleItemTouchHelperCallback 的实现，但我的猜测是它的 onMove() 实现返回 false。

于 2016-10-25T18:30:03.780 回答