Question

我使用android sqlite数据库创建了一个示例应用程序，我的要求是How can i use Sqlite database in my android activity?（请注意此链接）。我使用以下代码执行此操作，

MainClass.java

public class MainClass extends Activity implements OnClickListener {

    Button NUM_INPUT;
    EditText enter_NUM;
    int number;
    DatabaseHandler db = new DatabaseHandler(this);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.sai_answers_home);
        NUM_INPUT = (Button) findViewById(R.id.answerButton);
        enter_NUM = (EditText) findViewById(R.id.saiAnssersEditText);
        NUM_INPUT.setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        if (v.getId() == R.id.answerButton) {
             number = Integer.parseInt(this.enter_NUM.getText().toString());
            // /System.out.println("EDITTEXTVALUE" + number);
            Log.d("Reading: ", "Reading all contacts..");
            List<Contact> contacts = db.getAllContacts(number);
            for (Contact cn : contacts) {
                String log = "Id: " + cn.getID() + " ,Name: " + cn.getName();
                // Writing Contacts to log
                Log.d("Name: ", log);
            }
            db.close();
        }
    }
}

DataBaseHandler.java

   public class DatabaseHandler extends SQLiteOpenHelper {

        // The Android's default system path of your application database.
        private static String DB_PATH = "/data/data/com.sqlite.example/databases/";

        private static String DB_NAME = "answers";

        private SQLiteDatabase myDataBase;

        private final Context myContext;
        String myPath;

        /**
         * Constructor Takes and keeps a reference of the passed context in order to
         * access to the application assets and resources.
         * 
         * @param context
         */
        public DatabaseHandler(Context context) {

            super(context, DB_NAME, null, 1);
            this.myContext = context;
        }

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

            boolean dbExist = checkDataBase();

            if (dbExist) {
                // do nothing - database already exist
            } else {

                // By calling this method and empty database will be created into
                // the default system path
                // of your application so we are gonna be able to overwrite that
                // database with our database.
                this.getReadableDatabase();

                try {

                    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() {

            SQLiteDatabase checkDB = null;

            try {
                myPath = DB_PATH + DB_NAME;
                checkDB = SQLiteDatabase.openDatabase(myPath, null,
                        SQLiteDatabase.OPEN_READONLY);

            } catch (SQLiteException e) {

                // database does't exist yet.

            }

            if (checkDB != null) {

                checkDB.close();

            }

            return checkDB != null ? true : 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 {

            // Open your local db as the input stream
            InputStream myInput = myContext.getAssets().open(DB_NAME);

            // Path to the just created empty db
            String outFileName = DB_PATH + DB_NAME;

            // Open the empty db as the output stream
            OutputStream myOutput = new FileOutputStream(outFileName);

            // transfer bytes from the inputfile to the outputfile
            byte[] buffer = new byte[1024];
            int length;
            while ((length = myInput.read(buffer)) > 0) {
                myOutput.write(buffer, 0, length);
            }

            // Close the streams
            myOutput.flush();
            myOutput.close();
            myInput.close();

        }

        public void openDataBase() throws SQLException {

            // Open the database
            myPath = DB_PATH + DB_NAME;
            myDataBase = SQLiteDatabase.openDatabase(myPath, null,
                    SQLiteDatabase.OPEN_READONLY);

        }

        @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) {

        }

        // Add your public helper methods to access and get content from the
        // database.
        // You could return cursors by doing "return myDataBase.query(....)" so it'd
        // be easy
        // to you to create adapters for your views.

        public List<Contact> getAllContacts(int muNumber) {
            List<Contact> contactList = new ArrayList<Contact>();
            // Select All Query
            String selectQuery = "SELECT * FROM ANSWER WHERE ID= " + muNumber;
    System.out.println("QUERY STRING IS......>>>>>> " + selectQuery);

            SQLiteDatabase db = this.getWritableDatabase();
            Cursor cursor = db.rawQuery(selectQuery, null);

            // looping through all rows and adding to list
            if (cursor.moveToFirst()) {
                do {
                    Contact contact = new Contact();
                    contact.setID(Integer.parseInt(cursor.getString(0)));
                    contact.setName(cursor.getString(1));
                    // contact.setPhoneNumber(cursor.getString(2));
                    // Adding contact to list
                    contactList.add(contact);
                } while (cursor.moveToNext());
            }

            // return contact list
            return contactList;
        }
}

answers.db

database image

当我执行此代码时，我得到了错误，“android.database.sqlite.SQLiteException：没有这样的表：ANSWER :,编译时：SELECT * FROM ANSWER WHERE ID = 3”。我的确切要求是，当单击MainActivity类中的Button时，输入的值将传递给数据库。最后搜索数据库并返回数据库中存在的相应值。例如我输入2并单击按钮，从数据库我将得到“橙色”我怎么能实现这一点。提前谢谢。

Answer 1

您在变量DB_NAME =“answers”中提到了表名，在查询中，您尝试访问表名ANSWER。它唯一的拼写错误。

Answer 2

在您提到的“SELECT * FROM ANSWER WHERE ID =”

的选择查询中

但你必须提到“”SELECT * FROM answer WHERE ID“

因为表名不是答案

如何从android sqlite数据库中获取所选id的值？

2 个答案: