如何在Android SQLite中返回表格行

Question

I want for the time being just to return a row of my SQLite Table in my Android app(In Logcat).

I inserted a sample code based on SQlite tutorials I have read as follows:

1)I inserted that code into my main activity:

MySQLiteHelper db = new MySQLiteHelper(this);
    // add Books
    db.addBook(new Book("Android Application Development Cookbook", "Wei Meng Lee"));   
    db.addBook(new Book("Android Programming: The Big Nerd Ranch Guide", "Bill Phillips and Brian Hardy"));       
    db.addBook(new Book("Learn Android App Development", "Wallace Jackson"));

    // get all books
    //List<Book> list = db.getAllBooks();

    // delete one book
    //db.deleteBook(list.get(0));

    // get all books
    //db.getAllBooks();

2)I created a new class named MySQLiteHelper.java and I pasted that code:

package com.qualcomm.QCARSamples.ImageTargets;

import java.util.LinkedList;
import java.util.List;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class MySQLiteHelper extends SQLiteOpenHelper {

    // Database Version
    private static final int DATABASE_VERSION = 1;
    // Database Name
    private static final String DATABASE_NAME = "BookDB";

    public MySQLiteHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);  
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // SQL statement to create book table
        String CREATE_BOOK_TABLE = "CREATE TABLE books ( " +
                "id INTEGER PRIMARY KEY AUTOINCREMENT, " + 
                "title TEXT, "+
                "author TEXT )";

        // create books table
        db.execSQL(CREATE_BOOK_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Drop older books table if existed
        db.execSQL("DROP TABLE IF EXISTS books");

        // create fresh books table
        this.onCreate(db);
    }
    //---------------------------------------------------------------------

    /**
     * CRUD operations (create "add", read "get", update, delete) book + get all books + delete all books
     */

    // Books table name
    private static final String TABLE_BOOKS = "books";

    // Books Table Columns names
    private static final String KEY_ID = "id";
    private static final String KEY_TITLE = "title";
    private static final String KEY_AUTHOR = "author";

    private static final String[] COLUMNS = {KEY_ID,KEY_TITLE,KEY_AUTHOR};

    public void addBook(Book book){
        //for logging
Log.d("addBook", book.toString()); 

// 1. get reference to writable DB
SQLiteDatabase db = this.getWritableDatabase();

// 2. create ContentValues to add key "column"/value
ContentValues values = new ContentValues();
values.put(KEY_TITLE, book.getTitle()); // get title 
values.put(KEY_AUTHOR, book.getAuthor()); // get author

// 3. insert
db.insert(TABLE_BOOKS, // table
        null, //nullColumnHack
        values); // key/value -> keys = column names/ values = column values

// 4. close
db.close(); 
}

    public Book getBook(int id){

        // 1. get reference to readable DB
        SQLiteDatabase db = this.getReadableDatabase();

        // 2. build query
        Cursor cursor = 
                db.query(TABLE_BOOKS, // a. table
                COLUMNS, // b. column names
                " id = ?", // c. selections 
                new String[] { String.valueOf(id) }, // d. selections args
                null, // e. group by
                null, // f. having
                null, // g. order by
                null); // h. limit

        // 3. if we got results get the first one
        if (cursor != null)
            cursor.moveToFirst();

        // 4. build book object
        Book book = new Book();
        book.setId(Integer.parseInt(cursor.getString(0)));
        book.setTitle(cursor.getString(1));
        book.setAuthor(cursor.getString(2));

        //log 
    Log.d("getBook("+id+")", book.toString());

        // 5. return book
        return book;
    }
    // Get All Books
    public List<Book> getAllBooks() {
        List<Book> books = new LinkedList<Book>();

        // 1. build the query
        String query = "SELECT  * FROM " + TABLE_BOOKS;

        // 2. get reference to writable DB
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(query, null);

        // 3. go over each row, build book and add it to list
        Book book = null;
        if (cursor.moveToFirst()) {
            do {
                book = new Book();
                book.setId(Integer.parseInt(cursor.getString(0)));
                book.setTitle(cursor.getString(1));
                book.setAuthor(cursor.getString(2));

                // Add book to books
                books.add(book);
            } while (cursor.moveToNext());
        }

        Log.d("getAllBooks()", books.toString());

        // return books
        return books;
    }

     // Updating single book
    public int updateBook(Book book) {

        // 1. get reference to writable DB
        SQLiteDatabase db = this.getWritableDatabase();

        // 2. create ContentValues to add key "column"/value
        ContentValues values = new ContentValues();
        values.put("title", book.getTitle()); // get title 
        values.put("author", book.getAuthor()); // get author

        // 3. updating row
        int i = db.update(TABLE_BOOKS, //table
                values, // column/value
                KEY_ID+" = ?", // selections
                new String[] { String.valueOf(book.getId()) }); //selection args

        // 4. close
        db.close();

        return i;

    }
    // Deleting single book
    public void deleteBook(Book book) {

        // 1. get reference to writable DB
        SQLiteDatabase db = this.getWritableDatabase();

        // 2. delete
        db.delete(TABLE_BOOKS, //table name
                KEY_ID+" = ?",  // selections
                new String[] { String.valueOf(book.getId())}); //selections args

        // 3. close
        db.close();

        //log
    Log.d("deleteBook", book.toString());

    }



}

3)Finally I created a new class named Book.java including that code:

package com.qualcomm.QCARSamples.ImageTargets;

public class Book {

    private int id;
    private String title;
    private String author;

    public Book(){}

    public Book(String title, String author) {
        super();
        this.title = title;
        this.author = author;
    }

 // getting ID
    public int getId(){
        return this.id;
    }
 // getting name
    public String getAuthor(){
        return this.author;
    }
 // getting name
    public String getTitle(){
        return this.title;
    }


    // setting id
    public void setId(int id){
        this.id = id;
    }



    // setting name
    public void setTitle(String title){
        this.title = title;
    }

    // setting name
    public void setAuthor(String author){
        this.author = author;
    }
    //getters & setters

    @Override
    public String toString() {
        return "Book [id=" + id + ", title=" + title + ", author=" + author
                + "]";
    }

    }

In my code so far I am able to view my three rows of my SQLite Table in Logcat.

How do I return for example the 1st or the 2nd row of my SQLite Table?

Answer 1

You can try http://developer.android.com/reference/android/database/Cursor.html#moveToPosition%28int%29 but without an order by in your query (and a very consistent order by), this might not give you the same row every time you ask for says move to 2nd position. Even then, as the table gets updated, this keeps changing.

Answer 2

You can just query through Your table like this:

        Cursor cursor = 
        db.query(TABLE_BOOKS, new String[] {KEY_ID,KEY_TITLE,KEY_AUTHOR }, 
        null, null, null, null, null); 

with this, You get the complete entries of Your table. And then, it depends on You what exactly You want. If You want just a certain line:

  String currentTitle="";
  String currentAuthor="";

      int rows = Cursor.getCount();
      Cursor.moveToFirst();
      for(int i=0;i<rows;i++){

         int bookId = c.getInt(0);

          if(bookId==id){
             //now You got the entry and can get all informations You want
             currentTitle = cursor.getString(1);
             currentAuthor = cursor.getString(2);
             c.moveToNext();
          }
       }

It is only an example to know how You have to do it.