android - 使用 Itemtouchhelper 更改房间数据库的顺序

Question

我有一个使用 recyclerview 来显示数据库项目的应用程序。我想通过使用 itemtouchhelper 拖动来重新排列项目。我想出了如何做到这一点，但我不知道如何更新我的房间数据库。

ItemTouchHelper helper = new ItemTouchHelper(new ItemTouchHelper.SimpleCallback(ItemTouchHelper.LEFT|ItemTouchHelper.RIGHT|ItemTouchHelper.DOWN|ItemTouchHelper.UP, ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT) {

            int dragFrom = -1;
            int dragTo = -1;
            boolean listChanged = false;

            @Override
            public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder viewHolder1) {
                int from = viewHolder.getAdapterPosition();
                int to = viewHolder1.getAdapterPosition();

                if(dragFrom == -1) {
                    dragFrom =  from;
                }
                dragTo = to;
                listChanged = true;

                Collections.swap(mGames, from, to);
                gameAdapter.notifyItemMoved(from, to);

                return true;
            }

            @Override
            public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int i) {
                mGames.remove(viewHolder.getAdapterPosition());
                Game game = mGames.get(viewHolder.getAdapterPosition());
                mGameViewModel.deleteGame(game);
                gameAdapter.notifyItemRemoved(viewHolder.getAdapterPosition());
            }

            @Override
            public void onSelectedChanged(@Nullable RecyclerView.ViewHolder viewHolder, int actionState) {
                super.onSelectedChanged(viewHolder, actionState);

                if(actionState == ItemTouchHelper.ACTION_STATE_IDLE && listChanged){

                    //update database

                    listChanged = false;
                }
            }
        });

比如我把第 3 项拖到第 6 点，然后第 4 项变成第 3 项，第 5 项变成 4，第 6 项变成 5。

有没有一种特殊的方法，或者我必须自己找到一个？

Answer 1

一种简单的方法(但对于大型列表效率低下)是，一旦您获得新列表，清除数据库并重新插入项目(使用新的 id (PKeys))。还要确保仅在用户停止拖动时才进行数据库操作。还要确保您没有以任何特定顺序从数据库中查询项目。

        new ItemTouchHelper(new ItemTouchHelper.SimpleCallback(ItemTouchHelper.UP | ItemTouchHelper.DOWN, ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT) {

            boolean drag = false;

            @Override
            public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder target) {
                int position_dragged = viewHolder.getAdapterPosition();
                int position_target = target.getAdapterPosition();

                Collections.swap(mAdapter.getTasks(), position_dragged, position_target);
                mAdapter.notifyItemMoved(position_dragged, position_target);

                return false;
            }

            @Override
            public void onSelectedChanged(@Nullable RecyclerView.ViewHolder viewHolder, int actionState) {
                super.onSelectedChanged(viewHolder, actionState);

                if(actionState == ItemTouchHelper.ACTION_STATE_DRAG) {
                    drag = true;
                }

                if(actionState == ItemTouchHelper.ACTION_STATE_IDLE && drag) {
                    Log.d("DragTest","DRAGGGING stop");
                    drag= false;

                    final List<TaskEntry> NewTasksList =  mAdapter.getTasks();

                    AppExecutors.getInstance().diskIO().execute(new Runnable() {
                        @Override
                        public void run() {
                            mDb.taskDao().deleteAll();

                            for(int i =0; i < NewTasksList.size(); i++){
                                TaskEntry task = NewTasksList.get(i);
                                mDb.taskDao().insertTask(new TaskEntry(
                                        task.getDescription(),
                                        task.getPriority(),
                                        task.getUpdatedAt(),
                                        task.isChecked()
                                ));
                            }
                        }
                    });
                }
            }
        }).attachToRecyclerView(mRecyclerView);

默认情况下，Sqlite 按 primaryKey 的 ASC 顺序返回(在我的例子中是 ids)。因此，请确保不要插入具有旧 ID 的新项目。
我的TaskEntry.java

@Entity(tableName = "task")
public class TaskEntry {

    @PrimaryKey(autoGenerate = true)
    private int id;
    private String description;
    private int priority;
    @ColumnInfo(name = "updated_at")
    private Date updatedAt;
    private boolean checked;

    //When adding new entry to database, id is automatically generated
    @Ignore
    public TaskEntry(String description, int priority, Date updatedAt, boolean checked) {
        this.description = description;
        this.priority = priority;
        this.updatedAt = updatedAt;
        this.checked = checked;
    }

    //when reading from database
    public TaskEntry(int id, String description, int priority, Date updatedAt, boolean checked) {
        this.id = id;
        this.description = description;
        this.priority = priority;
        this.updatedAt = updatedAt;
        this.checked = checked;
    }

我的TaskDao.java

@Dao
public interface TaskDao{

//
    @Query("SELECT * FROM task")
    LiveData<List<TaskEntry>> loadAllTasks();

    @Insert
    void insertTask(TaskEntry taskEntry);

    @Update(onConflict = OnConflictStrategy.REPLACE)
    void updateTask(TaskEntry taskEntry);

    @Delete
    void deleteTask(TaskEntry taskEntry);

    @Query("DELETE FROM task")
    void deleteAll();

    @Query("SELECT * FROM task WHERE id = :id")
    LiveData<TaskEntry> loadTaskById(int id);
}