Question

当我第一次执行应用程序时，我的DbHelper会创建数据库。但是，当我稍后尝试打开数据库时（在同一个应用程序执行期间，在另一个活动中），再次创建数据库，因为checkDatabase（）返回false，当然，这会因为表存在而产生异常。当我第一次创建数据库时，我打开它并关闭它，所以我猜问题是文件没有刷新（这是第二次checkDatabase（）返回false的唯一原因。）

重要的是要说这只在第一次执行时发生。在“不幸，已停止”消息之后，数据库访问正常。任何想法???

Answer 1

您可以参考以下代码了解何时创建新数据库，检查现有数据库

public class DataBaseHelper extends SQLiteOpenHelper {

private static String DB_PATH;
private static String DB_NAME = "podcastDB.db";
private SQLiteDatabase myDataBase;
private final Context myContext;
SharedPreferences sharedPreferences;

public DataBaseHelper(Context context) {

    super(context, DB_NAME, null, 1);
    this.myContext = context;
    DB_PATH = "/data/data/" + myContext.getPackageName() + "/databases/";

    sharedPreferences = PreferenceManager
            .getDefaultSharedPreferences(myContext);
}

/**
 * Creates a empty database on the system and rewrites it with your own
 * database.
 * */
public void createDataBase() throws IOException {

    // ---Check whether database is already created or not---
    boolean dbExist = checkDataBase();

    if (dbExist) {
    } else {
        this.getReadableDatabase();
        try {
            // ---If not created then copy the database---
            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() {
    try {
        String myPath = DB_PATH + DB_NAME;
        File f = new File(myPath);
        if (f.exists())
            return true;
        else
            return false;
    } catch (SQLiteException e) {
        Log.e("Podcast", "There was an error", e);
        return 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 {

    InputStream myInput = myContext.getAssets().open(DB_NAME);

    String outFileName = DB_PATH + DB_NAME;

    OutputStream myOutput = new FileOutputStream(outFileName);

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

    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_READWRITE);

}

@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) {

}
}

SQLiteOpenHelper在首次执行时崩溃

1 个答案: