sqlite 数据库的帮助程序类不起作用

Question

我在我的活动中使用了以下代码，它检查数据库错误并且工作正常：

//DB Test
        Boolean databaseError = false;
        SQLiteDatabase myDB = null;
        myDB = this.openOrCreateDatabase("myDB", 0, null);        
        try {
             myDB.rawQuery("SELECT _id FROM occasions;", null);
             myDB.rawQuery("SELECT _id FROM instrumentations;", null); 
             myDB.rawQuery("SELECT _id FROM editions;", null); 
             myDB.rawQuery("SELECT _id FROM composers;", null); 
             myDB.rawQuery("SELECT _id FROM compositions;", null); 
        } catch (SQLiteException e) {
            Log.e("SQLiteException", "SQLiteException");
            databaseError = true;       
        }
        myDB.close();

我想把代码放在下面的帮助类中：

public abstract class BackupHelper {

public static boolean checkDB() {
    Boolean databaseError = false;
    SQLiteDatabase myDB = null;
    myDB = SQLiteDatabase.openDatabase("myDB", null, SQLiteDatabase.OPEN_READWRITE);        
    try {
         myDB.rawQuery("SELECT _id FROM occasions;", null);
         myDB.rawQuery("SELECT _id FROM instrumentations;", null); 
         myDB.rawQuery("SELECT _id FROM editions;", null); 
         myDB.rawQuery("SELECT _id FROM composers;", null); 
         myDB.rawQuery("SELECT _id FROM compositions;", null); 
    } catch (SQLiteException e) {
        Log.e("SQLiteException", "SQLiteException");
        databaseError = true;       
    }
    myDB.close();
    return databaseError;
}

}

但这会引发以下错误：

02-26 21:13:16.397: E/MyTestDatabase(29244): sqlite3_open_v2("myDB", &handle, 2, NULL) 失败 02-26 21:13:17.048: E/AndroidRuntime(29244): 原因: android.database.sqlite.SQLiteException: 无法打开数据库文件

Answer 1

您必须先创建数据库，然后再尝试打开它。

创建一个扩展 SQLiteOpenHelper 的类

public class DBCreator extends SQLiteOpenHelper {

    // region Properties

    private final static String tag = "DBCreator";

    // endregion

    // region Constructors

    public DBCreator(String name, int version) {
        super(ABApplication.getContext(), name, null, version);
    }

    public DBCreator(Context context, String name, CursorFactory factory,
            int version) {
        super(context, name, factory, version);
    }

    public DBCreator(Context context, String name, CursorFactory factory,
            int version, DatabaseErrorHandler errorHandler) {
        super(context, name, factory, version, errorHandler);
    }

    // endregion

    // region Overrides
    @Override
    public void onCreate(SQLiteDatabase db) {

        // Execute your CREATE Table script
    }

    // endregion 

}

那么你可以通过这种方式检索一个 SQLiteDatabase 实例：

 SQLiteDatabase SQLiteDatabase = new DBCreator(context, dbName, null, 1) getWritableDatabase();