我正在开发 android 应用程序。我的客户端为我提供了一个很大的数据库。它几乎是 2.3Mb。最初我不知道如何使用现有数据库，我遵循了本教程 教程
用于访问现有数据库。但我得到了错误。我想知道如何访问这种类型的大型数据库。谁能帮我。
在这里，我有我的 DataBaseHelper 类。
公共类 DataBaseHelper 扩展 SQLiteOpenHelper {
// The Android's default system path of your application database.
private static String DB_PATH = "/data/data/com.example.readdatabase/databases/";
private static String DB_NAME = "categories.sqlite";
private SQLiteDatabase myDataBase;
private final 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) {
// do nothing - database already exist
} else {
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
/**
* Check if the database already exist to avoid re-copying the file each
* time you open the application.
*
* @return true if it exists, false if it doesn't
*/
private boolean checkDataBase() {
SQLiteDatabase checkDB = null;
try {
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READONLY);
} catch (SQLiteException e) {
// database does't exist yet.
}
if (checkDB != null) {
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* Copies your database from your local assets-folder to the just created
* empty database in the system folder, from where it can be accessed and
* handled. This is done by transfering bytestream.
* */
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);
// transfer bytes from the inputfile to the outputfile
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) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
public Cursor performTransaction(String query) {
Cursor cur = myDataBase.rawQuery(query, null);
return cur;
}
}
这是我的主要课程
公共类 MainActivity 扩展 Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
DataBaseHelper db = new DataBaseHelper(this);
try {
db.createDataBase();
} catch (IOException e) {
e.printStackTrace();
}
db.openDataBase();
String query = "select * from PrayerInfo";
Cursor cursor = db.performTransaction(query);
System.out.println(cursor.getColumnCount());
}
}
它在 Android 2.3 和更高版本中运行良好。但它在较低版本上不起作用。我收到错误之类的错误。任何人都可以帮助我
java.lang.Error：在 com.example.readdatabase.MainActivity.onCreate(MainActivity.java:18) 的 com.example.readdatabase.DataBaseHelper.createDataBase(DataBaseHelper.java:48) 复制数据库时出错