我尝试了很多次在我的Android应用程序中使用现有的数据库sqlite！ 我可以创建一个新的数据库，但在这里，我想使用现有的数据库！ 这是我的代码，那里没有问题，没有错误， 但它不起作用，任何人都可以帮助我吗？
DataBaseHelper.java：
public class DataBaseHelper extends SQLiteOpenHelper {
private static String DB_PATH = "/data/data/com.global.getrain/databases/";
private static String DB_NAME = "BookDB";
private SQLiteDatabase myDataBase;
private Context myContext;
public DataBaseHelper(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
}
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist){
}else{
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
public boolean checkDataBase(){
SQLiteDatabase checkDB = null;
try{
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteException e){
}
if(checkDB != null){
checkDB.close();
}
return checkDB != null ? true : false;
}
private void copyDataBase() throws IOException{
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
}
//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
public void openDataBase() throws SQLException{
//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if(myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
// SQL statement to create book table
String CREATE_BOOK_TABLE = "CREATE TABLE books ( " + "id INTEGER PRIMARY KEY AUTOINCREMENT, " + "title TEXT, "
+ "author TEXT )";
// create books table
db.execSQL(CREATE_BOOK_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// Drop older books table if existed
db.execSQL("DROP TABLE IF EXISTS books");
// create fresh books table
this.onCreate(db);
}
// Books table name
private static final String TABLE_BOOKS = "books";
// Books Table Columns names
private static final String KEY_ID = "id";
private static final String KEY_TITLE = "title";
private static final String KEY_AUTHOR = "author";
private static final String[] COLUMNS = { KEY_ID, KEY_TITLE, KEY_AUTHOR };
public void addBook(Book book) {
Log.d("addBook", book.toString());
// 1. get reference to writable DB
SQLiteDatabase db = this.getWritableDatabase();
// 2. create ContentValues to add key "column"/value
ContentValues values = new ContentValues();
values.put(KEY_TITLE, book.getTitle()); // get title
values.put(KEY_AUTHOR, book.getAuthor()); // get author
// 3. insert
db.insert(TABLE_BOOKS, // table
null, // nullColumnHack
values); // key/value -> keys = column names/ values = column
// values
// 4. close
db.close();
}
public Book getBook(int id) {
// 1. get reference to readable DB
SQLiteDatabase db = this.getReadableDatabase();
// 2. build query
Cursor cursor = db.query(TABLE_BOOKS, // a. table
COLUMNS, // b. column names
" id = ?", // c. selections
new String[] { String.valueOf(id) }, // d. selections args
null, // e. group by
null, // f. having
null, // g. order by
null); // h. limit
// 3. if we got results get the first one
if (cursor != null)
cursor.moveToFirst();
// 4. build book object
Book book = new Book();
book.setId(Integer.parseInt(cursor.getString(0)));
book.setTitle(cursor.getString(1));
book.setAuthor(cursor.getString(2));
Log.d("getBook(" + id + ")", book.toString());
// 5. return book
return book;
}
// Get All Books
public List<Book> getAllBooks() {
List<Book> books = new LinkedList<Book>();
// 1. build the query
String query = "SELECT * FROM " + TABLE_BOOKS;
// 2. get reference to writable DB
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(query, null);
// 3. go over each row, build book and add it to list
Book book = null;
if (cursor.moveToFirst()) {
do {
book = new Book();
book.setId(Integer.parseInt(cursor.getString(0)));
book.setTitle(cursor.getString(1));
book.setAuthor(cursor.getString(2));
// Add book to books
books.add(book);
} while (cursor.moveToNext());
}
Log.d("getAllBooks()", books.toString());
// return books
return books;
}
// Updating single book
public int updateBook(Book book) {
// 1. get reference to writable DB
SQLiteDatabase db = this.getWritableDatabase();
// 2. create ContentValues to add key "column"/value
ContentValues values = new ContentValues();
values.put("title", book.getTitle()); // get title
values.put("author", book.getAuthor()); // get author
// 3. updating row
int i = db.update(TABLE_BOOKS, // table
values, // column/value
KEY_ID + " = ?", // selections
new String[] { String.valueOf(book.getId()) }); // selection
// args
// 4. close
db.close();
return i;
}
// Deleting single book
public void deleteBook(Book book) {
// 1. get reference to writable DB
SQLiteDatabase db = this.getWritableDatabase();
// 2. delete
db.delete(TABLE_BOOKS, KEY_ID + " = ?", new String[] { String.valueOf(book.getId()) });
// 3. close
db.close();
Log.d("deleteBook", book.toString());
}
}
MainActivity.java：
public class MainActivity extends Activity {
private ListView obj;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
DataBaseHelper db = new DataBaseHelper(this);
db = new DataBaseHelper(this);
try {
db.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
db.openDataBase();
} catch (SQLException sqle) {
throw sqle;
}
/*
* db.addBook(new Book("Android Application Development Cookbook",
* "Wei Meng Lee")); db.addBook(new Book(
* "Android Programming: The Big Nerd Ranch Guide",
* "Bill Phillips and Brian Hardy")); db.addBook(new Book(
* "Learn Android App Development", "Wallace Jackson"));
*
*
* // get all books List<Book> list = db.getAllBooks();
*
* // delete one book db.deleteBook(list.get(0));
*
* // get all books db.getAllBooks();
*/
obj = (ListView) findViewById(R.id.listView1);
List<Book> array_list = db.getAllBooks();
ArrayAdapter<Book> arrayAdapter = new ArrayAdapter<Book>(this, android.R.layout.simple_list_item_1, array_list);
obj.setAdapter(arrayAdapter);
db.close();
}
PS：我可以发布Book课程，如果有帮助的话！
答案 0 :(得分：0)
问题出在资产文件夹中，它必须是这样的：
资产/数据库/
我添加了数据库文件夹然后它工作：D