如何在android sqlite中删除单行

I have sqlite数据表示在ListView by a CustomListAdapter.单击一行时alert dialogue弹出提示用户删除单行sqlite在我的活动中：

private void deleteDialog() {
        AlertDialog.Builder alertDialog = new AlertDialog.Builder(MyCart.this);
        alertDialog.setCancelable(false);
        alertDialog.setMessage("Delete item?");
        alertDialog.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                myDb.deleteSingleContact(toString());
            }
        });
        alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                dialog.cancel();

            }
        });
        alertDialog.show();
    }

在我的 DBHelper.java 上：

 public void deleteSingleContact(String title){

        SQLiteDatabase db = this.getWritableDatabase();
        db.delete(CONTACTS_TABLE_NAME, CONTACTS_COLUMN_TITLE + "=?", new String[]{title});
//KEY_NAME is a column name
    }

然而上面的代码没有删除任何东西。我猜它是我没有正确完成的功能。有什么建议吗？

完整的 DBHelper.java

public class DBHelper extends SQLiteOpenHelper {

    public static final String DATABASE_NAME = "MyDBName.db";
    public static final String CONTACTS_TABLE_NAME = "contacts";
    public static final String CONTACTS_COLUMN_ID = "id";
    public static final String CONTACTS_COLUMN_TITLE = "title";
    public static final String CONTACTS_COLUMN_AMOUNT = "amount";
    public static final String CONTACTS_COLUMN_DESC = "description";

    private HashMap hp;

    public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub
        db.execSQL(
                "create table contacts " +
                        "(id integer primary key, title text,amount float,description text)"
        );
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub
        db.execSQL("DROP TABLE IF EXISTS contacts");
        onCreate(db);
    }

    public boolean insertContact(String title,  float amount, String description) {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();

        contentValues.put("title", title);
        contentValues.put("amount", amount);
        contentValues.put("description", description);


        db.insert("contacts", null, contentValues);
        return true;
    }

    public Cursor getData(int id) {
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor res = db.rawQuery("select * from contacts where id=" + id + "", null);
        return res;
    }

    public int numberOfRows() {
        String countQuery = "SELECT  * FROM " + CONTACTS_TABLE_NAME;
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(countQuery, null);
        int cnt = cursor.getCount();
        cursor.close();
        return cnt;
    }

    public boolean updateContact(Integer id, String title, float amount, String description) {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put("title", title);
        contentValues.put("amount", amount);
        contentValues.put("description", description);

        db.update("contacts", contentValues, "id = ? ", new String[]{Integer.toString(id)});
        return true;
    }

    public void deleteContact() {
        SQLiteDatabase db = this.getWritableDatabase();
        db.delete("contacts", null, null);
        db.close();
    }

    public void deleteSingleContact(String title){

        SQLiteDatabase db = this.getWritableDatabase();
        db.delete(CONTACTS_TABLE_NAME, CONTACTS_COLUMN_TITLE + "=?", new String[]{title});
//KEY_NAME is a column name
    }

    public boolean checkForTables() {
        boolean hasRows = false;
        SQLiteDatabase db = getReadableDatabase();
        Cursor cursor = db.rawQuery("SELECT COUNT(*) FROM " + CONTACTS_TABLE_NAME, null);
        cursor.moveToFirst();
        int count = cursor.getInt(0);
        if(count > 0)
            hasRows = true;
        db.close();
        return hasRows;
    }
    public ArrayList<ContactListItems> getAllContacts() {
        ArrayList<ContactListItems> contactList = new ArrayList<>();
        hp = new HashMap();
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor res = db.rawQuery("select * from contacts", null);
        res.moveToFirst();
        while (!res.isAfterLast()) {
                ContactListItems contactListItems = new ContactListItems();

                contactListItems.setTitle(res.getString(res
                        .getColumnIndex("title")));
                contactListItems.setAmount(res.getFloat(res
                        .getColumnIndex("amount")));
                contactListItems.setDescription(res.getString(res
                        .getColumnIndex("description")));
                contactList.add( contactListItems);
                res.moveToNext();
            }
        res.close();
        return contactList;
    }
    public int getTotalOfAmount(){
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor c=db.rawQuery("SELECT SUM(amount) FROM " +CONTACTS_TABLE_NAME,null);
        c.moveToFirst();
        int i=c.getInt(0);
        c.close();
        return i;
    }
}

EDIT

obj.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
            @Override
            public boolean onItemLongClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
                deleteDialog();
                return true;
            }
        });
    }

日志猫错误：

android.database.sqlite.SQLiteException: near "=": syntax error (code 1): , while compiling: DELETE FROM contacts WHERE title=
            at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
            at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:882)
            at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:493)
            at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
            at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
            at android.database.sqlite.SQLiteStatement.<init>(SQLiteStatement.java:31)
            at android.database.sqlite.SQLiteDatabase.executeSql(SQLiteDatabase.java:1663)
            at android.database.sqlite.SQLiteDatabase.execSQL(SQLiteDatabase.java:1594)
            at com.softtech.stevekamau.buyathome.DBHelper.removeSingleContact(DBHelper.java:157)
            at com.softtech.stevekamau.buyathome.MyCart$6.onClick(MyCart.java:140)
            at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:166)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4745)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
            at dalvik.system.NativeStart.main(Native Method)

您可以使用 SQL DELETE 语句来选择要删除的条目。 使用字符串值作为选择器时，请确保将该值括在''.

    /**
     * Remove a contact from database by title
     *
     * @param title to remove
     */
    public void removeSingleContact(String title) {
        //Open the database
        SQLiteDatabase database = this.getWritableDatabase();

        //Execute sql query to remove from database
        //NOTE: When removing by String in SQL, value must be enclosed with ''
        database.execSQL("DELETE FROM " + TABLE_NAME + " WHERE " + CONTACTS_COLUMN_TITLE + "= '" + title + "'");

        //Close the database
        database.close();
    }

然后，每当您想从数据库中删除条目时，请使用以下命令：

DBHelper dbHelper = new DBHelper(context);
dbHelper.removeSingleContact("CONTACT_TO_REMOVE_HERE");

UPDATE假设你的ListView数据集是一个ArrayList包含 ContactListItems，您可以设置OnItemClickListener为您ListView并用它来获取您选择的标题，然后将其删除。

listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

    @Override
    public void onItemClick(AdapterView<?> parent, View view, final int position, long id) {

        AlertDialog.Builder alertDialog = new AlertDialog.Builder(MyCart.this);
        alertDialog.setCancelable(false);
        alertDialog.setMessage("Delete item?");
        alertDialog.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                String title;

                title = arrayList.get(position).getTitle();

                dbHelper.removeSingleContact(title);

                //Update your ArrayList
                arrayList = dbHelper.getAllContacts();

                //Notify your ListView adapter
                adapter.notifyDataSetChanged();

            }
        });
        alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                dialog.cancel();
            }
        });
        alertDialog.show();

    }

});