Android Sqlite 问题

Question

我正在尝试实现一个在 Android10 上找到的 SQLite 示例.

代码工作正常，直到我向原始代码添加了两列，然后它崩溃了。 这是在我向它添加了另外两列之后的 DBAdapter，它们是 from 和 link

public class DBAdapter 
{
    public static final String KEY_ROWID = "_id";
    public static final String KEY_ISBN = "isbn";
    public static final String KEY_TITLE = "title";
    public static final String KEY_FROM = "from";
    public static final String KEY_LINK = "link";
    public static final String KEY_PUBLISHER = "publisher";    
    private static final String TAG = "DBAdapter";

    private static final String DATABASE_NAME = "books";
    private static final String DATABASE_TABLE = "titles";
    private static final int DATABASE_VERSION = 1;

    private static final String DATABASE_CREATE =
        "create table titles (_id integer primary key autoincrement, "
        + "isbn text not null, title text not null, from text not null, link text not null"
        + "publisher text not null);";

    private final Context context; 

    private DatabaseHelper DBHelper;
    private SQLiteDatabase db;

    public DBAdapter(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) 
        {
            db.execSQL(DATABASE_CREATE);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, 
        int newVersion) 
        {
            Log.w(TAG, "Upgrading database from version " + oldVersion 
                    + " to "
                    + newVersion + ", which will destroy all old data");
            db.execSQL("DROP TABLE IF EXISTS titles");
            onCreate(db);
        }
    }    

    //---opens the database---
    public DBAdapter open() throws SQLException 
    {
        db = DBHelper.getWritableDatabase();
        return this;
    }

    //---closes the database---    
    public void close() 
    {
        DBHelper.close();
    }

    //---insert a title into the database---
    public long insertTitle(String isbn, String title,String from, String link, String publisher) 
    {
        ContentValues initialValues = new ContentValues();
        initialValues.put(KEY_ISBN, isbn);
        initialValues.put(KEY_TITLE, title);
        initialValues.put(KEY_FROM, from);
        initialValues.put(KEY_LINK, link);
        initialValues.put(KEY_PUBLISHER, publisher);
        return db.insert(DATABASE_TABLE, null, initialValues);
    }

    //---deletes a particular title---
    public boolean deleteTitle(long rowId) 
    {
        return db.delete(DATABASE_TABLE, KEY_ROWID + 
                "=" + rowId, null) > 0;
    }

    //---retrieves all the titles---
    public Cursor getAllTitles() 
    {
        return db.query(DATABASE_TABLE, new String[] {
                KEY_ROWID, 
                KEY_ISBN,
                KEY_TITLE,
                KEY_FROM,
                KEY_LINK,
                KEY_PUBLISHER}, 
                null, 
                null, 
                null, 
                null, 
                null);
    }

    //---retrieves a particular title---
    public Cursor getTitle(long rowId) throws SQLException 
    {
        Cursor mCursor =
                db.query(true, DATABASE_TABLE, new String[] {
                        KEY_ROWID,
                        KEY_ISBN, 
                        KEY_TITLE,
                        KEY_FROM,
                        KEY_LINK,
                        KEY_PUBLISHER
                        }, 
                        KEY_ROWID + "=" + rowId, 
                        null,
                        null, 
                        null, 
                        null, 
                        null);
        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;
    }

    //---updates a title---
    public boolean updateTitle(long rowId, String isbn, 
    String title, String from, String link, String publisher) 
    {
        ContentValues args = new ContentValues();
        args.put(KEY_ISBN, isbn);
        args.put(KEY_TITLE, title);
        args.put(KEY_FROM, from);
        args.put(KEY_LINK, link);
        args.put(KEY_PUBLISHER, publisher);
        return db.update(DATABASE_TABLE, args, 
                         KEY_ROWID + "=" + rowId, null) > 0;
    }
}

这是我添加两列后的DatabaseActivity

public class DatabaseActivity extends Activity {
    /** Called when the activity is first created. */

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

        DBAdapter db = new DBAdapter(this);

        //---add 2 titles---
        db.open();        
        long id;
        id = db.insertTitle(
                "0470285818",
                "Hanudi is the best :)",
                "Wrox",
                "www.wrox.com",
                "WroxWrox");        
        id = db.insertTitle(
                "047017661X",
                "Professional Windows Vista Gadgets Programming",
                "Wrox",
                "www.wrox2.com",
                "WroxWrox2");
        db.close();

        //---get all titles---
        db.open();
        Cursor c = db.getAllTitles();
        if (c.moveToFirst())
        {
            do {          
                DisplayTitle(c);
            } while (c.moveToNext());
        }
        db.close();
    }    
    public void DisplayTitle(Cursor c)
    {
        Toast.makeText(this, 
                "id: " + c.getString(0) + "\n" +
                "ISBN: " + c.getString(1) + "\n" +
                "TITLE: " + c.getString(2) + "\n" +
                "FROM: " + c.getString(3) + "\n" +
                "LINK: " + c.getString(4) + "\n" +
                "PUBLISHER:  " + c.getString(5),
                Toast.LENGTH_LONG).show();        
    }    
}

Answer 1

2 个可能让您悲伤的问题:

1. 确保您的DATABASE_CREATE 中有足够的逗号!目前 null 和 publisher 之间没有逗号。如果您在 SQLite 管理工具中运行它，这将引发错误，并且可能是导致崩溃的原因。你的字符串最终是:

   ...., link text not nullpublisher text not null

2. 您正在尝试使用 SQL 保留关键字 FROM 作为列名。这可能是您今后的第二个问题。最佳做法是为您的列选择一个命名合理且有意义的名称。也许将其称为 fromCustomer 或 fromYear 或更具描述性的名称。