Android 数据库 - 没有这样的表错误

Question

我正在尝试使用一些 http 请求来为 android 应用程序填充数据库中的一些表。当填充这些表时，表中的部分数据将填充并扩展 View 。问题是我收到一条错误消息，告诉我我尝试创建的表未创建。

错误日志:

01-05 13:33:29.811: E/SQLiteLog(1823): (1) no such table: lvl2List

01-05 13:33:29.831: E/AndroidRuntime(1823): android.database.sqlite.SQLiteException: no such table: lvl2List (code 1): , while compiling: SELECT id, Title, Description FROM lvl2List

这是我的代码:

MainActivity.java

public class MainActivity extends Activity 
{
    private List<lvItem> myLVItems = new ArrayList<lvItem>();
    private List<Parent> myParent = new ArrayList<Parent>();
    ExpandableListView exv;
    final DBHelper db2 = new DBHelper(this);
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        exv=(ExpandableListView)findViewById(R.id.expandableListView1);
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        db2.open();

        lvl3 lvl3Item = new lvl3();
        lvl3Item.popDB(db2, myParent);
    }
}

DBHelper.java

public class DBHelper 
{
    private static final String Database_Name = "MyDBs";
    private static final int Database_Version = 2;

    public static final String Key_ID = "id";
    public static final String Key_Title = "Title";
    public static final String Key_Summary = "Summary";
    public static final String Key_Book = "Book";
    public static final String Key_Chapter = "Chapter";
    public static final String Key_Description = "Description";
    public static final String Key_SourceType = "SourceType";

    private static final String Lvl3_Table_Name = "lvl3";
    private static final String Lvl2_Table_Name = "lvl2List";
    private static final String Lvl1_Table_Name = "lvl1List";

    private static final String Lvl3_Create = "CREATE TABLE IF NOT EXISTS lvl3 (id integer primary key autoincrement, "
        +"Summary VARCHAR, Book VARCHAR, Chapter VARCHAR, Description VARCHAR, SourceType VARCHAR);";
    private static final String Lvl2_Create = "CREATE TABLE IF NOT EXISTS lvl2List (id integer primary key autoincrement, "
        +"Title VARCHAR, Description VARCHAR);";
    private static final String Lvl1_Create = "CREATE TABLE IF NOT EXISTS lvl1List (id integer primary key autoincrement, "
        +"Title VARCHAR, Description VARCHAR);";

    public DBHelper(Context ctx) {
        this.context = ctx;
        DBhelper = new DatabaseHelper(context);
    }

    private static class DatabaseHelper extends SQLiteOpenHelper
    {
        DatabaseHelper(Context context)
        {
            super(context, Database_Name, null, Database_Version);
        }

        @Override
        public void onCreate(SQLiteDatabase db) 
        {
            try
            {
                db.execSQL(Lvl3_Create);
                db.execSQL(Lvl2_Create);
                db.execSQL(Lvl1_Create);
            }catch(SQLException e){

            }

        }

        public long insertLvl2Record(String Title, String Description)
        {
            ContentValues initialValues = new ContentValues();
            initialValues.put(Key_Title, Title); 
            initialValues.put(Key_Description, Description); 

            return db.insert(Lvl2_Table_Name, null, initialValues);
        }

        public long insertLvl3Record(String Summary, String Book, String Chapter, String Description, String SourceType)
        {
            ContentValues initialValues = new ContentValues();
            initialValues.put(Key_Summary, Summary); 
            initialValues.put(Key_Book, Book); 
            initialValues.put(Key_Chapter, Chapter); 
            initialValues.put(Key_Description, Description); 
            initialValues.put(Key_SourceType, SourceType); 

            return db.insert(Lvl3_Table_Name, null, initialValues);
        }

        public int getLvl2Count()
        {
            Cursor c = db.query(Lvl2_Table_Name, new String[] {Key_ID, Key_Title,Key_Description}, 
            null, null, null, null, null);

            return c.getCount();
        }

        public int getLvl3Count()
        {
            Cursor c = db.query(Lvl3_Table_Name, new String[] {Key_ID, Key_Summary,Key_Book,Key_Verse,Key_Scripts,Key_Description,Key_SourceType}, null, null, null, null, null);

            return c.getCount();
        }

lvl3.java

public class lvl3
{
    DBHelper db2;
    List<Parent> parent;
    public void popDB(DBHelper db, List<Parent> myParent) 
    {
        this.db2 = db;
        this.parent = myParent;
        Lvl3Thread lvl3theard = new Lvl3Thread();
        lvl3theard.execute();
    }
    public class Lvl3Thread extends AsyncTask<String, Integer, String>{
        @Override
        protected String doInBackground(String... params) 
        {
            //Httprequest that get the data for the database… this works
        }
        @Override
        protected void onPostExecute(String result) 
        {
            lvl2 lvl2Item = new lvl2();
            lvl2Item.popDB(db2, parent);
        }
    }
}

lvl2.java

public class lvl3
{
    DBHelper db2;
    List<Parent> parent;
    public void popDB(DBHelper db, List<Parent> myParent) 
    {
        this.db2 = db;
        this.parent = myParent;
        Lvl3Thread lvl3theard = new Lvl3Thread();
        lvl3theard.execute();
    }
    public class Lvl3Thread extends AsyncTask<String, Integer, String>{
        @Override
        protected String doInBackground(String... params) 
        {
            //Httprequest that get the data for the database… this works
        }
        @Override
        protected void onPostExecute(String result) 
        {
            lvl2 lvl2Item = new lvl2();
            lvl2Item.popDB(db2, parent);
        }
    }
    public void popLvl2List(DBHelper db)
    {
        List<lvItem> childlvItems = new ArrayList<lvItem>();
        Cursor cLvl3 = db.getAllLvl3Records();
        db.getLvl2Count(); //This is where the error is coming from stating that there is no lvl2List table
    }
}

我已经尝试使用 db2.detLvl2Count(); 但它不起作用。如果我注释掉 行，程序就会运行。我尝试重新排序 db.execSQL，以便 db.execSQL(Lvl2_Create); 排在第一位，但我仍然收到该表不存在的错误。

Answer 1

您的 DBHelper 类的

onCreate 只会在您第一次打开应用程序并调用该类时被调用。

您后来是否碰巧添加了 lvl2List 表？

如果是这样，请尝试重新安装应用程序并重试。

添加/更改 SQL 表时，使用 onUpgrade 方法。查看official documentation

此外，在 DBHelper 的 onCreate 方法中，您正在“吃掉”SQLException - 不要这样做 - 它可能很有趣给你的信息 ;-)

通过吃掉 Exception 我的意思是，您“静静地”处理异常并继续前进。

这是 DatabaseHelper 的 onCreate 方法:

@Override
public void onCreate(SQLiteDatabase db) {
    try {
        db.execSQL(Lvl3_Create);
        db.execSQL(Lvl2_Create);
        db.execSQL(Lvl1_Create);
    } catch (SQLException e) {
        // Handle a possible exception here.
    }
}

注意 catch 子句。在这里您至少应该执行 e.printStacktrace(); 或 Log.e(e);。

在你的情况下，你可能没有从这个日志中得到任何东西，因为 onCreate 方法只在你第一次安装和启动应用程序时被调用。

查看此 SO post关于这个问题或只是搜索 Google - 这是我们作为程序员倾向于做的一个已知“问题”/“行为”；-)

可以找到关于如何处理异常的好线索 here .