AsyncTaskLoader的onStartLoading（）没有被调用

Question

我有这个自定义Loader，它应该使用内容解析器插入我在数据库中发送给它的一些虚拟数据。我在活动中使用getLoaderManager().initLoader(INSERT_DUMMY_DATA_ID, null, this); 。调用构造函数。但是没有调用onStartLoading（）和loadinBackgroung（）。

这是ProductInsertionLoader.java

public class ProductInsertionLoader extends AsyncTaskLoader {
private String LOG_TAG = ProductInsertionLoader.class.getSimpleName();
private ArrayList<ContentValues> mValues;
private ContentResolver mContentResolver;

public ProductInsertionLoader(Context context, ContentResolver contentResolver, ArrayList<ContentValues> values) {
    super(context);
    mValues = values;
    mContentResolver = contentResolver;
    Log.v(LOG_TAG, "constructor called");
}

@Override
public Object loadInBackground() {
    Log.v(LOG_TAG, "loadInBackground() called");
    ArrayList<Uri> uris = new ArrayList<>();
    for (ContentValues value : mValues) {
        Uri uri = mContentResolver.insert(ProductContract.ProductEntry.CONTENT_URI, value);
        Log.v(LOG_TAG, "Dummy data inserted. ID: " + ContentUris.parseId(uri));
        uris.add(uri);
    }
    return null;
}

@Override
protected void onStartLoading() {
    Log.v(LOG_TAG, "onStartLoading() called");
    forceLoad();
}

}

以下是我在CatalogActivity.java中调用它的方法

package com.example.android.inventory;

import android.app.LoaderManager;
import android.content.ContentResolver;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.CursorLoader;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.Loader;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.ActionMode;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AbsListView;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import com.example.android.inventory.data.ProductContract.ProductEntry;
import com.example.android.inventory.data.ProductInsertionLoader;

import java.io.IOException;
import java.util.ArrayList;

public class CatalogActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<Cursor> {
    private static final String LOG_TAG = CatalogActivity.class.getSimpleName();
    private ProductCursorAdapter mCursorAdapter;
    private static final int URL_LOADER = 0;
    private static final int INSERT_DUMMY_DATA_ID = 1;
    private Uri mCurrentProductUri;
    private ArrayList<ContentValues> mValues;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_catalog);
    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(CatalogActivity.this, EditorActivity.class);
            startActivity(intent);
        }
    });

    final ListView listView = (ListView) findViewById(R.id.list_view_product);
    TextView textView = (TextView) findViewById(R.id.empty_view);
    listView.setEmptyView(textView);
    mCursorAdapter = new ProductCursorAdapter(this, null, getContentResolver());
    listView.setAdapter(mCursorAdapter);

    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            Intent intent = new Intent(CatalogActivity.this, EditorActivity.class);
            Uri currentProductUri = ContentUris.withAppendedId(ProductEntry.CONTENT_URI, id);
            intent.setData(currentProductUri);
            startActivity(intent);
        }
    });


    getLoaderManager().initLoader(URL_LOADER, null, CatalogActivity.this);
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.menu_catalog, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case R.id.action_insert_dummy_data:
            insertDummyData();
            return true;
        case R.id.action_delete_all_entries:
            showDeleteConfirmationDialog("Delete all products?", null);
            return true;
    }
    return super.onOptionsItemSelected(item);
}

private void insertDummyData() {
    mValues = new ArrayList<>();
    mValues.add(getContentValues("Sugar", 50, 60, "Sweet Sugar Company", R.drawable.sugar));
    mValues.add(getContentValues("Salt", 20, 30, "Salty Salt Company", R.drawable.salt));
    mValues.add(getContentValues("Bread", 45, 20, "Nanglo", R.drawable.bread));
    mValues.add(getContentValues("Biscuit", 75, 20, "GoodDay", R.drawable.biscuit));
    mValues.add(getContentValues("Noodles", 15, 200, "CupMen", R.drawable.noodles));
    mValues.add(getContentValues("Milk", 33, 100, "DDC", R.drawable.milk));
    mValues.add(getContentValues("Cheese", 80, 30, "Amul", R.drawable.cheese));

    getLoaderManager().initLoader(INSERT_DUMMY_DATA_ID, null, this).forceLoad();

    Toast.makeText(this, "Dummy Data Inserted", Toast.LENGTH_SHORT).show();
}

private ContentValues getContentValues(String name, int price, int quantity, String supplier, int resId) {
    ContentValues values = new ContentValues();
    values.put(ProductEntry.COLUMN_NAME, name);
    values.put(ProductEntry.COLUMN_PRICE, price);
    values.put(ProductEntry.COLUMN_QUANTITY, quantity);
    values.put(ProductEntry.COLUMN_SUPPLIER, supplier);

    //Uri for the sugar drawable
    Uri imageUri = Uri.parse(ContentResolver.SCHEME_ANDROID_RESOURCE +
            "://" + getResources().getResourcePackageName(resId)
            + '/' + getResources().getResourceTypeName(resId)
            + '/' + getResources().getResourceEntryName(resId));
    Bitmap bitmap = null;
    //Converting the sugar image into a thumbnail
    try {
        bitmap = DbBitmapUtility.getThumbnail(imageUri, this);
    } catch (IOException e) {
        e.printStackTrace();
    }
    //Converting the sugar thumbnail into a byte array.
    byte[] image = DbBitmapUtility.getBitmapAsByteArray(bitmap);

    values.put(ProductEntry.COLUMN_IMAGE, image);
    return values;
}



@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
    switch (id) {
        case URL_LOADER:
            String[] projection = {
                    ProductEntry._ID,
                    ProductEntry.COLUMN_NAME,
                    ProductEntry.COLUMN_QUANTITY,
                    ProductEntry.COLUMN_PRICE,
                    ProductEntry.COLUMN_SUPPLIER,
                    ProductEntry.COLUMN_IMAGE
            };
            return new CursorLoader(
                    this,
                    ProductEntry.CONTENT_URI,
                    projection,
                    null,
                    null,
                    null);
        case INSERT_DUMMY_DATA_ID:
            new ProductInsertionLoader(this, getContentResolver(), mValues);
            return null;
        default:
            Log.v(LOG_TAG, "onCreateLoader: Invalid id");
            return null;

    }
}

@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
    if (loader.getId() == URL_LOADER) {
        mCursorAdapter.swapCursor(data);
    } else return;
}

@Override
public void onLoaderReset(Loader<Cursor> loader) {
    mCursorAdapter.swapCursor(null);

}

}

如你所见，我正在使用两个装载机。一个CursorLoader将所有数据库数据加载到UI中，另一个自定义AsyncTaskLoader将一些虚拟数据插入到后台线程上的数据库中。 为什么自定义加载器的onStartLoading（）或loadInBackground（）没有被调用？