我对创建和操作数据库非常陌生，我似乎被卡住了，我的 logcat 一直告诉我它无法打开数据库？
09-12 13:02:31.823: I/SqliteDatabaseCpp(7213): sqlite 返回：错误代码 = 14，msg = 无法在 [8609a15dfa] 的第 27701 行打开文件，db=/data/data/net.learn2develop.Database/数据库/数据库
我猜它找不到它，但我知道为什么。感谢你们中的许多人，到目前为止，我已经按照自己的方式工作了，但仍然卡住了，我的代码正在做的是导入我从资产文件夹中创建的数据库。这是我的数据库助手类：
public class DatabaseHelper extends SQLiteOpenHelper {
public static final String KEY_ROWID = "_id";
public static final String KEY_ALCOHOL = "alcohol";
public static final String KEY_TYPE = "type";
public static final String KEY_BRAND = "brand";
public static final String KEY_PRICE = "price";
private static final String TAG = "DatabaseHelper";
private static String DB_PATH = "/data/data/net.learn2develop.Database/databases/";
private static String DB_NAME = "database";
private static final String DB_TABLE = "booze";
private SQLiteDatabase myDataBase;
private final Context myContext;
/**
* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
* @param context
*/
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
}
/**
* Creates a empty database on the system and rewrites it with your own database.
* */
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist){
//do nothing - database already exist
}else{
//By calling this method and empty database will be created into the default system path
//of your application so we are gonna be able to overwrite that database with our database.
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 myDataBase) {
}
@Override
public void onUpgrade(SQLiteDatabase myDataBase, int oldVersion, int newVersion) {
Log.w(TAG, "Upgrading database from version " + oldVersion
+ " to "
+ newVersion + ", which will destroy all old data");
myDataBase.execSQL("DROP TABLE IF EXISTS titles");
onCreate(myDataBase);
}
//---insert a title into the database---
public long insertTitle(String alcohol, String type, String brand, int price)
{
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_ALCOHOL, alcohol);
initialValues.put(KEY_TYPE, type);
initialValues.put(KEY_BRAND, brand);
initialValues.put(KEY_PRICE, price);
return myDataBase.insert(DB_TABLE, null, initialValues);
}
//---retrieves a particular title---
public Cursor getTitle(long rowId) throws SQLException
{
Cursor mCursor =
myDataBase.query(true, DB_TABLE, new String[] {
KEY_ROWID,
KEY_ALCOHOL,
KEY_TYPE,
KEY_BRAND,
KEY_PRICE
},
KEY_ROWID + "=" + rowId,
null,
null,
null,
null,
null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
这是我在活动中调用的内容，以测试我是否可以读取数据库：
public class DatabaseActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_database);
DatabaseHelper myDbHelper = new DatabaseHelper(this);
//---get a title---
myDbHelper.openDataBase();
Cursor c = myDbHelper.getTitle(2);
if (c.moveToFirst())
DisplayTitle(c);
else
Toast.makeText(this, "No title found",
Toast.LENGTH_LONG).show();
myDbHelper.close();
}
public void DisplayTitle(Cursor c)
{
Toast.makeText(this,
"id: " + c.getString(0) + "\n" +
"ALCOHOL: " + c.getString(1) + "\n" +
"TYPE: " + c.getString(2) + "\n" +
"BRAND: " + c.getString(3) + "\n" +
"PRICE: " + c.getString(4),
Toast.LENGTH_LONG).show();
}
}
我创建的数据库的名称只是“数据库”，活动是“DatabaseActivity.java”，帮助文件是“DatabaseHelper.java”
这是我的数据库的样子
