我正在开发一个小应用程序，用于在数据库中保存书籍的数据（例如书籍的名称，书籍的类型，书籍的作者和出版年份），但是当数据使用 CursorLoader 从数据库返回它在 ListView
中显示两次这是 AddBook 活动的代码。
package training.android.com.librarycard;
import android.app.AlertDialog;
import android.app.LoaderManager;
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.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.NavUtils;
import android.support.v7.app.AppCompatActivity;
import android.text.TextUtils;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.Toast;
import training.android.com.librarycard.Database.Database;
import training.android.com.librarycard.Database.LibraryCardContract;
public class AddBook extends AppCompatActivity
implements LoaderManager.LoaderCallbacks<Cursor> {
private static final int EXISTING_BOOK_LOADER = 0;
Spinner mBookType;
EditText mBookTitle, mBookAuthor, mBookPublishYear;
String bookType;
int position;
private boolean bookHasChanged = false;
private Uri currentBookUri;
private View.OnTouchListener touchListener = new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
bookHasChanged = true;
return false;
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_add_book);
Intent intent = getIntent();
if (intent != null) {
currentBookUri = intent.getData();
if (currentBookUri == null) {
setTitle("Add a book");
invalidateOptionsMenu();
} else {
setTitle("Edit a book");
getLoaderManager().initLoader(EXISTING_BOOK_LOADER, null, this);
}
}
mBookType = findViewById(R.id.spinner);
mBookTitle = findViewById(R.id.book_title);
mBookAuthor = findViewById(R.id.book_author);
mBookPublishYear = findViewById(R.id.publish_year);
mBookType.setOnTouchListener(touchListener);
mBookAuthor.setOnTouchListener(touchListener);
mBookTitle.setOnTouchListener(touchListener);
mBookPublishYear.setOnTouchListener(touchListener);
setupBookTypeSpinner();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.home, menu);
return true;
}
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
super.onPrepareOptionsMenu(menu);
if (currentBookUri == null) {
MenuItem menuItem = menu.findItem(R.id.action_delete);
menuItem.setVisible(false);
}
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
switch (id) {
case R.id.action_save:
setBook();
finish();
return true;
case R.id.action_delete:
showDeleteConfirmationDialog();
return true;
case android.R.id.home:
if (!bookHasChanged) {
NavUtils.navigateUpFromSameTask(AddBook.this);
return true;
}
DialogInterface.OnClickListener discardButtonClickListener
= new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
NavUtils.navigateUpFromSameTask(AddBook.this);
}
};
showUnsavedChangeDialog(discardButtonClickListener);
return true;
}
return super.onOptionsItemSelected(item);
}
private void showUnsavedChangeDialog(DialogInterface.OnClickListener discardButtonClickListener) {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Discard your changes and quit editing?");
builder.setPositiveButton("Discard", discardButtonClickListener);
builder.setNegativeButton("Keep editing", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
if (dialog != null)
dialog.dismiss();
}
});
AlertDialog alertDialog = builder.create();
alertDialog.show();
}
private void showDeleteConfirmationDialog() {
final AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Delete this book ?");
builder.setPositiveButton("Delete", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
deleteBook();
}
});
builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
if (dialog != null)
dialog.dismiss();
}
});
AlertDialog alertDialog = builder.create();
alertDialog.show();
}
private void deleteBook() {
if (currentBookUri != null) {
int rowDeleted = getContentResolver().delete(currentBookUri, null, null);
if (rowDeleted == 0)
Toast.makeText(this, "Delete book failed", Toast.LENGTH_SHORT).show();
else
Toast.makeText(this, "Delete book successful", Toast.LENGTH_SHORT).show();
}
finish();
}
public void setupBookTypeSpinner() {
final ArrayAdapter<CharSequence> bookTypeAdapter = ArrayAdapter.createFromResource(
this, R.array.books_type, R.layout.support_simple_spinner_dropdown_item);
bookTypeAdapter.setDropDownViewResource(android.R.layout.simple_dropdown_item_1line);
mBookType.setAdapter(bookTypeAdapter);
mBookType.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
bookType = parent.getSelectedItem().toString();
position = parent.getSelectedItemPosition();
Log.i("BookTypeSelection", bookType+"");
}
@Override
public void onNothingSelected(AdapterView<?> parent) {
}
});
}
public void setBook() {
String bookTitle = mBookTitle.getText().toString().trim();
String bookAuthor = mBookAuthor.getText().toString().trim();
String publishYear = mBookPublishYear.getText().toString().trim();
if (currentBookUri == null && TextUtils.isEmpty(bookTitle) && TextUtils.isEmpty(bookAuthor)
&& TextUtils.isEmpty(publishYear))
return;
Database database = new Database(this);
SQLiteDatabase db = database.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(LibraryCardContract.LibraryCard.COLUMN_BOOK_TITLE, bookTitle);
values.put(LibraryCardContract.LibraryCard.COLUMN_BOOK_AUTHOR, bookAuthor);
values.put(LibraryCardContract.LibraryCard.COLUMN_BOOK_PUBLISH_YEAR, publishYear);
values.put(LibraryCardContract.LibraryCard.COLUMN_BOOK_TYPE, bookType);
if (currentBookUri == null) {
Uri uri = getContentResolver().insert(LibraryCardContract.LibraryCard.CONTENT_URI, values);
if (uri == null) {
Toast.makeText(this, "Error with saving book", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(this, "Book saved", Toast.LENGTH_SHORT).show();
}
} else {
int rowAffected = getContentResolver().update(currentBookUri, values, null, null);
if (rowAffected == 0) {
Toast.makeText(this, "Error with saving book", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(this, "Book saved", Toast.LENGTH_SHORT).show();
}
}
db.insert(LibraryCardContract.LibraryCard.TABLE_NAME, null, values);
Toast.makeText(this, "Insert new book", Toast.LENGTH_SHORT).show();
}
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
String [] projection = {
LibraryCardContract.LibraryCard.COLUMN_BOOK_TITLE,
LibraryCardContract.LibraryCard.COLUMN_BOOK_TYPE,
LibraryCardContract.LibraryCard.COLUMN_BOOK_AUTHOR,
LibraryCardContract.LibraryCard.COLUMN_BOOK_PUBLISH_YEAR };
return new CursorLoader(this,currentBookUri,projection,
null,null,null);
}
@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
if(data.moveToFirst()){
String title = data.getString(
data.getColumnIndexOrThrow(LibraryCardContract.LibraryCard.COLUMN_BOOK_TITLE));
String type = data.getString(
data.getColumnIndexOrThrow(LibraryCardContract.LibraryCard.COLUMN_BOOK_TYPE));
String publishYear = data.getString(
data.getColumnIndexOrThrow(LibraryCardContract.LibraryCard.COLUMN_BOOK_PUBLISH_YEAR));
String author = data.getString(
data.getColumnIndexOrThrow(LibraryCardContract.LibraryCard.COLUMN_BOOK_AUTHOR));
mBookTitle.setText(title);
mBookAuthor.setText(author);
mBookType.setSelection(position);
mBookPublishYear.setText(publishYear);
}
}
@Override
public void onLoaderReset(Loader<Cursor> loader) {
mBookTitle.setText("");
mBookType.setSelection(position);
mBookAuthor.setText("");
mBookPublishYear.setText("");
}
@Override
public void onBackPressed() {
if(!bookHasChanged){
super.onBackPressed();
return;
}
DialogInterface.OnClickListener discardButtonClickListener =
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
finish();
}
};
showUnsavedChangeDialog(discardButtonClickListener);
}
}
这是主页活动的代码，其中包含 listView 显示数据。
package training.android.com.librarycard;
import android.app.LoaderManager;
import android.content.ContentUris;
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.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import java.util.ArrayList;
import java.util.List;
import training.android.com.librarycard.Database.Database;
import training.android.com.librarycard.Database.LibraryCardContract;
import training.android.com.librarycard.Models.BookCursorAdapter;
import training.android.com.librarycard.Models.BookDetail;
public class Home extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener, LoaderManager.LoaderCallbacks<Cursor> {
private static final int BOOK_LOADER = 0;
private ListView mBookList;
private BookCursorAdapter cursorAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
mBookList = findViewById(R.id.books_rv);
cursorAdapter = new BookCursorAdapter(this, null);
mBookList.setAdapter(cursorAdapter);
mBookList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Intent intent = new Intent(Home.this, AddBook.class);
Uri currentPetUri = ContentUris.withAppendedId(LibraryCardContract.LibraryCard.CONTENT_URI, id);
intent.setData(currentPetUri);
startActivity(intent);
}
});
getLoaderManager().initLoader(BOOK_LOADER, null, this);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(getBaseContext(), AddBook.class);
startActivity(intent);
}
});
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.addDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
switch (id) {
case R.id.delete_all_books:
deleteAllBooks();
return true;
}
//noinspection SimplifiableIfStatement
return super.onOptionsItemSelected(item);
}
private void deleteAllBooks() {
int rowDeleted = getContentResolver().delete(LibraryCardContract.LibraryCard.CONTENT_URI,
null, null);
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
String[] projection = {
LibraryCardContract.LibraryCard._ID,
LibraryCardContract.LibraryCard.COLUMN_BOOK_TITLE,
LibraryCardContract.LibraryCard.COLUMN_BOOK_AUTHOR,
LibraryCardContract.LibraryCard.COLUMN_BOOK_TYPE,
LibraryCardContract.LibraryCard.COLUMN_BOOK_PUBLISH_YEAR};
return new CursorLoader(this, LibraryCardContract.LibraryCard.CONTENT_URI,
projection,
null,
null,
null);
}
@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
cursorAdapter.swapCursor(data);
}
@Override
public void onLoaderReset(Loader<Cursor> loader) {
cursorAdapter.swapCursor(null);
}
}
> This is a code of **BookCursorAdapter** class.
package training.android.com.librarycard.Models;
import android.content.Context;
import android.database.Cursor;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.CursorAdapter;
import android.widget.TextView;
import training.android.com.librarycard.Database.LibraryCardContract;
import training.android.com.librarycard.R;
/**
* Created by Hassan on 4/9/2018.
*/
public class BookCursorAdapter extends CursorAdapter {
public BookCursorAdapter(Context context, Cursor c) {
super(context, c, 0);
}
@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {
return LayoutInflater.from(context)
.inflate(R.layout.book_list,parent,false);
}
@Override
public void bindView(View view, Context context, Cursor cursor) {
TextView bookTitle = view.findViewById(R.id.book_name_tv);
TextView bookAuthor = view.findViewById(R.id.author_tv);
TextView bookType = view.findViewById(R.id.book_type_tv);
TextView publishYear = view.findViewById(R.id.publish_year_tv);
String title = cursor.getString(
cursor.getColumnIndexOrThrow(LibraryCardContract.LibraryCard.COLUMN_BOOK_TITLE));
String type = cursor.getString(
cursor.getColumnIndexOrThrow(LibraryCardContract.LibraryCard.COLUMN_BOOK_TYPE));
String year = cursor.getString(
cursor.getColumnIndexOrThrow(LibraryCardContract.LibraryCard.COLUMN_BOOK_PUBLISH_YEAR));
String author = cursor.getString(
cursor.getColumnIndexOrThrow(LibraryCardContract.LibraryCard.COLUMN_BOOK_AUTHOR));
bookAuthor.setText(author);
bookTitle.setText(title);
bookType.setText(type);
publishYear.setText(year);
}
@Override
public int getCount() {
return super.getCount();
}
}
应用程序的屏幕截图 enter image description here
