我在代码中得到了这个错误，说doInBackground方法中有一个错误，而我的代码中没有使用AsyncTask，相反，我使用Loader从SQLite数据库加载数据，我如何在代码中没有在任何地方使用或调用的方法中得到错误。
当我试图按下floatingaction按钮打开另一个活动时会出现错误，我有两种模式用于此活动，这取决于用户要更新或添加宠物。
package com.example.android.pets;
import android.app.LoaderManager;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Context;
import android.content.CursorLoader;
import android.content.Intent;
import android.content.Loader;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import com.example.android.pets.data.PetContract.PetEntry;
/**
* Displays list of pets that were entered and stored in the app.
*/
public class CatalogActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<Cursor>{
//loader unique ID
public static final int PET_LOADER = 0;
// If non-null, this is the current filter the user has provided.
private String mCurFilter;
// This is the Adapter being used to display the list's data.
private PetCursorAdapter mAdapter;
@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) {
startActivity(new Intent(CatalogActivity.this,EditorActivity.class));
}
});
// 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);
mAdapter = new PetCursorAdapter(this,null);
petListView.setAdapter(mAdapter);
getLoaderManager().initLoader(PET_LOADER,null,this);
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 contentUri = ContentUris.withAppendedId(PetEntry.CONTENT_URI,id);
intent.setData(contentUri);
startActivity(intent);
}
});
}
/**
* Helper method to insert hardcoded pet data into the database. For debugging purposes only.
*/
private void insertPet() {
// Create a ContentValues object where column names are the keys,
// and Toto's pet attributes are the values.
ContentValues values = new ContentValues();
values.put(PetEntry.COLUMN_PET_NAME, "Toto");
values.put(PetEntry.COLUMN_PET_BREED, "Promenader");
values.put(PetEntry.COLUMN_PET_GENDER, PetEntry.GENDER_MALE);
values.put(PetEntry.COLUMN_PET_WEIGHT, 7);
// Insert a new row for Toto into the provider using the ContentResolver.
// Use the {@link PetEntry#CONTENT_URI} to indicate that we want to insert
// into the pets database table.
// Receive the new content URI that will allow us to access Toto's data in the future.
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 i, Bundle bundle) {
// This is called when a new Loader needs to be created. This
// sample only has one Loader, so we don't care about the ID.
// First, pick the base URI to use depending on whether we are
// currently filtering.
Uri baseUri;
if (mCurFilter != null) {
baseUri = Uri.withAppendedPath(PetEntry.CONTENT_URI,
Uri.encode(mCurFilter));
} else {
baseUri = PetEntry.CONTENT_URI;
}
String [] projection = {PetEntry._ID,PetEntry.COLUMN_PET_NAME,PetEntry.COLUMN_PET_BREED};
return new CursorLoader(getApplication(), baseUri,
projection, null, null,
null );
}
@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
// Swap the new cursor in. (The framework will take care of closing the
// old cursor once we return.)
mAdapter.swapCursor(data);
}
@Override
public void onLoaderReset(Loader<Cursor> loader) {
// This is called when the last Cursor provided to onLoadFinished()
// above is about to be closed. We need to make sure we are no
// longer using it.
mAdapter.swapCursor(null);
}
}.
区块报价
public class EditorActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<Cursor> {
/** Create an instance from @link{PetDbHelper}*/
PetDbHelper mDbHelper;
/** EditText field to enter the pet's name */
private EditText mNameEditText;
/** Content URI for the existing pet (null if it's a new pet) */
private Uri mCurrentPetUri;
/** EditText field to enter the pet's breed */
private EditText mBreedEditText;
/** EditText field to enter the pet's weight */
private EditText mWeightEditText;
/** EditText field to enter the pet's gender */
private Spinner mGenderSpinner;
//the unique id of the loader
private final static int EXISTING_PET_LOADER = 0;
/**
* Gender of the pet. The possible values are:
* 0 for unknown gender, 1 for male, 2 for female.
*/
private int mGender = 0;
// get the title of the activity inside a variable
private CharSequence activityTitle = getTitle();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_editor);
Intent intent = getIntent();
mCurrentPetUri = intent.getData();
if (mCurrentPetUri == null){
setTitle(R.string.editor_activity_title_new_pet);
}else {
setTitle(R.string.editor_activity_edit_pet);
}
// Find all relevant views that we will need to read user input from
mNameEditText = (EditText) findViewById(R.id.edit_pet_name);
mBreedEditText = (EditText) findViewById(R.id.edit_pet_breed);
mWeightEditText = (EditText) findViewById(R.id.edit_pet_weight);
mGenderSpinner = (Spinner) findViewById(R.id.spinner_gender);
// To access our database, we instantiate our subclass of SQLiteOpenHelper
// and pass the context, which is the current activity.
mDbHelper = new PetDbHelper(this);
getLoaderManager().initLoader(EXISTING_PET_LOADER, null, this);
setupSpinner();
}
/**
* Setup the dropdown spinner that allows the user to select the gender of the pet.
*/
private void setupSpinner() {
// Create adapter for spinner. The list options are from the String array it will use
// the spinner will use the default layout
ArrayAdapter genderSpinnerAdapter = ArrayAdapter.createFromResource(this,
R.array.array_gender_options, android.R.layout.simple_spinner_item);
// Specify dropdown layout style - simple list view with 1 item per line
genderSpinnerAdapter.setDropDownViewResource(android.R.layout.simple_dropdown_item_1line);
// Apply the adapter to the spinner
mGenderSpinner.setAdapter(genderSpinnerAdapter);
// Set the integer mSelected to the constant values
mGenderSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
String selection = (String) parent.getItemAtPosition(position);
if (!TextUtils.isEmpty(selection)) {
if (selection.equals(getString(R.string.gender_male))) {
mGender = PetEntry.GENDER_MALE; // Male
} else if (selection.equals(getString(R.string.gender_female))) {
mGender = PetEntry.GENDER_FEMALE; // Female
} else {
mGender = PetEntry.GENDER_UNKNOWN; // Unknown
}
}
}
// Because AdapterView is an abstract class, onNothingSelected must be defined
@Override
public void onNothingSelected(AdapterView<?> parent) {
mGender = 0; // Unknown
}
});
}
/**
* Get user input from editor and save new pet into database.
*/
private void savePet() {
// Read from input fields
// Use trim to eliminate leading or trailing white space
String nameString = mNameEditText.getText().toString().trim();
String breedString = mBreedEditText.getText().toString().trim();
String weightString = mWeightEditText.getText().toString().trim();
// If the weight is not provided by the user, don't try to parse the string into an
// integer value. Use 0 by default.
int weight = 0;
if (!TextUtils.isEmpty(weightString)) {
weight = Integer.parseInt(weightString);
}
if (mCurrentPetUri == null &&
TextUtils.isEmpty(nameString) && TextUtils.isEmpty(breedString) &&
TextUtils.isEmpty(weightString) && mGender == PetEntry.GENDER_UNKNOWN) {return;}
// Create a ContentValues object where column names are the keys,
// and pet attributes from the editor are the values.
ContentValues values = new ContentValues();
values.put(PetEntry.COLUMN_PET_NAME, nameString);
values.put(PetEntry.COLUMN_PET_BREED, breedString);
values.put(PetEntry.COLUMN_PET_GENDER, mGender);
values.put(PetEntry.COLUMN_PET_WEIGHT, weight);
// Determine if this is a new or existing pet by checking if mCurrentPetUri is null or not
if (mCurrentPetUri == null) {
// This is a NEW pet, so insert a new pet into the provider,
// returning the content URI for the new pet.
Uri newUri = getContentResolver().insert(PetEntry.CONTENT_URI, values);
// Show a toast message depending on whether or not the insertion was successful.
if (newUri == null) {
// If the new content URI is null, then there was an error with insertion.
Toast.makeText(this, getString(R.string.editor_insert_pet_failed),
Toast.LENGTH_SHORT).show();
} else {
// Otherwise, the insertion was successful and we can display a toast.
Toast.makeText(this, getString(R.string.editor_insert_pet_successful),
Toast.LENGTH_SHORT).show();
}
}else {
// Otherwise this is an EXISTING pet, so update the pet with content URI: mCurrentPetUri
// and pass in the new ContentValues. Pass in null for the selection and selection args
// because mCurrentPetUri will already identify the correct row in the database that
// we want to modify.
int rowsAffected = getContentResolver().update(mCurrentPetUri, values, null, null);
// Show a toast message depending on whether or not the update was successful.
if (rowsAffected == 0) {
// If no rows were affected, then there was an error with the update.
Toast.makeText(this, getString(R.string.editor_update_pet_failed),
Toast.LENGTH_SHORT).show();
} else {
// Otherwise, the update was successful and we can display a toast.
Toast.makeText(this, getString(R.string.editor_update_pet_successful),
Toast.LENGTH_SHORT).show();
}
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu options from the res/menu/menu_editor.xml file.
// This adds menu items to the app bar.
getMenuInflater().inflate(R.menu.menu_editor, 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 "Save" menu option
case R.id.action_save:
//save pet for data base
savePet();
finish();
return true;
// Respond to a click on the "Delete" menu option
case R.id.action_delete:
// Do nothing for now
return true;
// Respond to a click on the "Up" arrow button in the app bar
case android.R.id.home:
// Navigate back to parent activity (CatalogActivity)
NavUtils.navigateUpFromSameTask(this);
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public Loader <Cursor> onCreateLoader(int id, Bundle args) {
// Since the editor shows all pet attributes, define a projection that contains
// all columns from the pet table
String[] projection = {
PetEntry._ID,
PetEntry.COLUMN_PET_NAME,
PetEntry.COLUMN_PET_BREED,
PetEntry.COLUMN_PET_GENDER,
PetEntry.COLUMN_PET_WEIGHT };
// This loader will execute the ContentProvider's query method on a background thread
return new CursorLoader(this, // Parent activity context
mCurrentPetUri, // Query the content URI for the current pet
projection, // Columns to include in the resulting Cursor
null, // No selection clause
null, // No selection arguments
null); // Default sort order
}
@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) {
if (cursor.moveToFirst()) {
// Find the columns of pet attributes that we're interested in
int nameColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_NAME);
int breedColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_BREED);
int genderColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_GENDER);
int weightColumnIndex = cursor.getColumnIndex(PetEntry.COLUMN_PET_WEIGHT);
// Extract out the value from the Cursor for the given column index
String name = cursor.getString(nameColumnIndex);
String breed = cursor.getString(breedColumnIndex);
int gender = cursor.getInt(genderColumnIndex);
int weight = cursor.getInt(weightColumnIndex);
// Update the views on the screen with the values from the database
mNameEditText.setText(name);
mBreedEditText.setText(breed);
mWeightEditText.setText(Integer.toString(weight));
// Gender is a dropdown spinner, so map the constant value from the database
// into one of the dropdown options (0 is Unknown, 1 is Male, 2 is Female).
// Then call setSelection() so that option is displayed on screen as the current selection.
switch (gender) {
case PetEntry.GENDER_MALE:
mGenderSpinner.setSelection(1);
break;
case PetEntry.GENDER_FEMALE:
mGenderSpinner.setSelection(2);
break;
default:
mGenderSpinner.setSelection(0);
break;
}
}
}
@Override
public void onLoaderReset(Loader<Cursor> loader) {
// If the loader is invalidated, clear out all the data from the input fields.
mNameEditText.setText("");
mBreedEditText.setText("");
mWeightEditText.setText("");
mGenderSpinner.setSelection(0); // Select "Unknown" gender
}
}。
08-04 04:28:57.457 11642-11900/com.example.android.pets E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #7
Process: com.example.android.pets, PID: 11642
java.lang.RuntimeException: An error occurred while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:353)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:383)
at java.util.concurrent.FutureTask.setException(FutureTask.java:252)
at java.util.concurrent.FutureTask.run(FutureTask.java:271)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
at java.lang.Thread.run(Thread.java:764)
Caused by: java.lang.NullPointerException: uri
at com.android.internal.util.Preconditions.checkNotNull(Preconditions.java:128)
at android.content.ContentResolver.query(ContentResolver.java:737)
at android.content.ContentResolver.query(ContentResolver.java:704)
at android.content.CursorLoader.loadInBackground(CursorLoader.java:64)
at android.content.CursorLoader.loadInBackground(CursorLoader.java:54)
at android.content.AsyncTaskLoader.onLoadInBackground(AsyncTaskLoader.java:315)
at android.content.AsyncTaskLoader$LoadTask.doInBackground(AsyncTaskLoader.java:69)
at android.content.AsyncTaskLoader$LoadTask.doInBackground(AsyncTaskLoader.java:64)
at android.os.AsyncTask$2.call(AsyncTask.java:333)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
at java.lang.Thread.run(Thread.java:764)
您没有直接使用asynctask，但AsyncTaskLoader类正在使用它。您必须学习读取日志。上面写着"老兄，你没有在URI中发送任何内容，因此后台进程失败了"。