android - 无法访问以前创建的 SQLite 数据库

Question

我正在创建一个应用程序，我必须在其中打开之前创建的 SQLite 数据库。我正在使用 DBHelper 类。当我模拟应用程序时一切正常，但 logcat 显示以下错误:

10-31 17:59:56.345: I/Database(391): sqlite returned: error code = 14, msg = cannot open file at source line 25467
10-31 17:59:56.345: E/Database(391): sqlite3_open_v2("/data/data/com.proj.neuroq/databases/quiz.db", &handle, 1, NULL) failed

我的 Activity 类:

public class QuestionActivity extends Activity {

    String db_name="quiz";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_question);

        DatabaseHelper myDbHelper = new DatabaseHelper(getBaseContext());
        myDbHelper = new DatabaseHelper(this);

        try {

            myDbHelper.createDatabase();

    } catch (IOException ioe) {

        throw new Error("Unable to create database");

    }

    try {

        myDbHelper.openDataBase();

    }catch(SQLException sqle){

        throw sqle;

    }



    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_question, menu);
        return true;
    }


}

我的 DatabaseHelper 类:

public class DatabaseHelper extends SQLiteOpenHelper {

    private static String DB_PATH = "/data/data/com.proj.neuroq/databases/";
    private static String DB_NAME = "quiz.db";
    private SQLiteDatabase db;
    private final Context myContext;

    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 dosen'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) {

        }

        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;
        db = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
    }

    @Override
    public synchronized void close() {
        if(db != null)
            db.close();

        super.close();
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub

    }

}

我的 list 文件:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.proj.neuroq"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="15" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".QuestionActivity"
            android:label="@string/title_activity_question" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

这是我的项目结构:

这是我的logcat 输出

我提到的链接:

http://www.reigndesign.com/blog/using-your-own-sqlite-database-in-android-applications/

http://snipplr.com/view.php?codeview&id=58589

棘手的问题在哪里？

Answer 1

你应该用这样的东西替换你的 checkDataBase() 方法:

public boolean checkDataBase()
{
    File dbFile = new File(DB_PATH + DB_NAME);
    return dbFile.exists();
}

如本文中所建议:http://www.itsalif.info/content/check-if-database-exist-android-sqlite3openv2-failed