加载程序管理器错误

Question

每当我使用 getLoaderManager().initLoader() 方法调用 LoaderManager 时，我都会收到错误的第三个参数类型的错误消息。我将 this 作为第三个参数传递。谁能告诉我为什么会出现此错误。我在 onCreate() 方法的末尾调用了 LoaderManager。下面是我的代码：

public class CatalogActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<Cursor> {

    private static final int PET_LOADER = 0;

    PetCursorAdapter mCursorAdapter;

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

        // Setup FAB to open EditorActivity
        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(CatalogActivity.this, EditorActivity.class);
                startActivity(intent);
            }
        });

        // Find the ListView which will be populated with the pet data
        ListView petListView = (ListView) findViewById(R.id.list);

        // Find and set empty view on the ListView, so that it only shows when the list has 0 items.
        View emptyView = findViewById(R.id.empty_view);
        petListView.setEmptyView(emptyView);

        mCursorAdapter = new PetCursorAdapter(this, null);
        petListView.setAdapter(mCursorAdapter);

        petListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {
                Intent intent = new Intent(CatalogActivity.this, EditorActivity.class);

                Uri currentPetUri = ContentUris.withAppendedId(PetEntry.CONTENT_URI, id);

                intent.setData(currentPetUri);

                startActivity(intent);
            }
        });

        getLoaderManager().initLoader(PET_LOADER, null, this);
    }

    private void insertPet() {

        ContentValues values = new ContentValues();
        values.put(PetEntry.COLUMN_NAME, "Toto");
        values.put(PetEntry.COLUMN_BREED, "Terrier");
        values.put(PetEntry.COLUMN_GENDER, PetEntry.GENDER_MALE);
        values.put(PetEntry.COLUMN_WEIGHT, 7);

        Uri newUri = getContentResolver().insert(PetEntry.CONTENT_URI, values);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu options from the res/menu/menu_catalog.xml file.
        // This adds menu items to the app bar.
        getMenuInflater().inflate(R.menu.menu_catalog, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // User clicked on a menu option in the app bar overflow menu
        switch (item.getItemId()) {
            // Respond to a click on the "Insert dummy data" menu option
            case R.id.action_insert_dummy_data:
                insertPet();
                return true;
            // Respond to a click on the "Delete all entries" menu option
            case R.id.action_delete_all_entries:
                // Do nothing for now
                return true;
        }
        return super.onOptionsItemSelected(item);
    }

    @Override
    public Loader<Cursor> onCreateLoader(int id, Bundle args) {

        String[] projection = {PetEntry._ID,
                PetEntry.COLUMN_NAME,
                PetEntry.COLUMN_BREED};

        return new CursorLoader(this,
                PetEntry.CONTENT_URI,
                projection,
                null,
                null,
                null);
    }

    @Override
    public void onLoadFinished(Loader<Cursor> loader, Cursor data) {

        mCursorAdapter.swapCursor(data);
    }

    @Override
    public void onLoaderReset(Loader<Cursor> loader) {

        mCursorAdapter.swapCursor(null);
    }
}

Answer 1

加载程序由 Android 框架 (android.app) 和 Android 支持库 (android.support.v4.app) 提供。它们不可互换，因此您需要选择使用哪一个，并确保您在给定位置使用的所有组件（例如 activity）都来自同一个包。

AppCompatActivity 提供了使用两者的能力 - getLoaderManager() returns 框架组件 (android.app.LoaderManager) 而 getSupportLoaderManager() returns 支持库组件 (android.support.v4.app.LoaderManager).

正如您在评论中提到的，您正在从支持库中导入 LoaderManager.LoaderCallbacks 组件。我认为你遇到的问题是你试图将它与框架中的 LoaderManager 组件一起使用（通过 getLoaderManager()）。

尝试将 getLoaderManager() 更改为 getSupportLoaderManager()。或者，如果出于某种原因您不想使用支持库，则需要导入 android.app.LoaderManager。

加载程序管理器错误

Loader Manager error

database

android

loader