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Question

我在服务器上有一个数据库作为应用内追求。 下载：

private static boolean downloadDatabase(Context context) {
    try {
           // Log.d(TAG, "downloading database");
            URL url = new URL("http://url/");
            /* Open a connection to that URL. */
            URLConnection ucon = url.openConnection();
            /*
             * Define InputStreams to read from the URLConnection.
             */
            InputStream is = ucon.getInputStream();
            BufferedInputStream bis = new BufferedInputStream(is);
            /*
             * Read bytes to the Buffer until there is nothing more to read(-1).
             */
            ByteArrayBuffer baf = new ByteArrayBuffer(50);
            int current = 0;
            while ((current = bis.read()) != -1) {
                    baf.append((byte) current);
            }

            /* Convert the Bytes read to a String. */
            FileOutputStream fos = null;
            // Select storage location
            fos = context.openFileOutput(Global.getName(), Context.MODE_PRIVATE); 

            fos.write(baf.toByteArray());
            fos.close();
           // Log.d(TAG, "downloaded");
    } catch (IOException e) {
            Log.e(TAG, "downloadDatabase Error: " , e);
            return false;
    }  catch (NullPointerException e) {
            Log.e(TAG, "downloadDatabase Error: " , e);
            return false;
    } catch (Exception e){
            Log.e(TAG, "downloadDatabase Error: " , e);
            return false;
    }
    return true;

这是DBHelper，数据库正在复制到data / data / ... dir。

public class DBHelper extends SQLiteOpenHelper { 

private static String DB_PATH = "/data/data/mypackage/databases";
public static String DB_NAME = Global.getName();
private static final int DB_VERSION = 1;
private static final String SP_KEY_DB_VER = "db_ver";

private SQLiteDatabase db; 
private  Context context;

 public DBHelper(Context context) {

        super(context, DB_NAME, null, DB_VERSION);
        this.context = context;
        initialize();
    }   

    private void initialize() {
        if (databaseExists()) {
            SharedPreferences prefs = PreferenceManager
                    .getDefaultSharedPreferences(context);
            int dbVersion = prefs.getInt(SP_KEY_DB_VER, 1);
            if (DB_VERSION != dbVersion) {
                File dbFile = context.getDatabasePath(DB_NAME);
                if (!dbFile.delete()) {
                    Log.w("MY APP", "Unable to update database");
                }
            }
        }
        if (!databaseExists()) {
            createDatabase();
        }
    }

    private boolean databaseExists() {
        File dbFile = context.getDatabasePath(DB_NAME);
        Log.e("TAG","database exist?"+dbFile.exists());
        return dbFile.exists();
    }

    /**
     * Creates database by copying it from assets directory.
     */
    private void createDatabase() {
        String parentPath = context.getDatabasePath(DB_NAME).getParent();
        String path = context.getDatabasePath(DB_NAME).getPath();
        File file = new File(parentPath);
        if (!file.exists()) {
            if (!file.mkdir()) {
                Log.w("MY APP", "Unable to create database directory");
                return;
            }
        }

        InputStream is = null;
        OutputStream os = null;
        try {
            is = context.openFileInput(Global.getDictionary());
            os = new FileOutputStream(path);

            byte[] buffer = new byte[1024];
            int length;
            while ((length = is.read(buffer)) > 0) {
                os.write(buffer, 0, length);
            }
            os.flush();

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (is != null) {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (os != null) {
                try {
                    os.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }


    public void openDataBase() throws SQLException{

        String myPath = DB_PATH + DB_NAME;
        db= SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);

    }


    @Override
    public synchronized void close() {

            if(db != null)
                db.close();

            super.close();

    }




public String getStr() {
    databaseExists();
    SQLiteDatabase db = this.getReadableDatabase();
    String s=null;
    Cursor c = db.rawQuery("SELECT indexStr from tablename where id=2 ",null);
    while (c.moveToNext()) {  
          s = c.getString(0);
    }  
    c.close();  
    db.close();  
    return s; 
}



@Override
public void onCreate(SQLiteDatabase arg0) {}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {}  

我看到，我的应用程序在下载数据库后占用了更多的内存空间，但是当我运行任何SELECT时返回“（1）没有这样的表”，但数据库存在。可能是数据库空了，但为什么呢？ 附：写入WRITE_EXTERNAL_STORAGE / READ_EXTERNAL_STORAGE的所有权限。

Answer 1

我认为你的表名不正确

  Cursor c = db.rawQuery("SELECT indexStr from tablename where id=2 ",null);

表的名称确实是＆＃34; tablename＆＃34; ???

检查

的值

public static String DB_NAME = Global.getName();

可能你正在阅读不同的数据库！。

Answer 2

尝试将此代码添加到onCreate（）方法并查看错误是否消失。

SQLiteDatabase db2 = openOrCreateDatabase("dbname", Context.MODE_PRIVATE, null);
    db2.execSQL("CREATE TABLE IF NOT EXISTS table_name(row1 INT PRIMARY KEY, row2 VARCHAR, row3 VARCHAR, row4 VARCHAR, );"); 

如果是，那意味着您的表格不是按照您之前尝试的方式创建的。

检查数据库是否已填充的最佳方法是单击DDMS并检查是否在项目下创建了数据库文件。如果已创建，请从设备中提取文件，然后通过SQLite数据库浏览器查看该文件，例如SQLiteBrowser