android 数据库sqllite示例

这篇文章写得好, 行文简洁, 清晰, 内容详尽. 一个例子可将你一脚踢进android数据库大门. 剩下的就是搭积木了.

Objectives:

• How to start using SQLite API?
• How to create new database & database tables?
• How to perform CRUD “Create, Read, Update and Delete” operations?

Environment & Tools:

• Android Developer Tools (ADT) (or Eclipse + ADT plugin)
• AVD Nexus S Android 4.3 “emulator”
• Min SDK 8
  

What we are building here?

We will build an App that can store & retrieve books title and author name.

( 1 ) Create Android Application

• File >> New >> Android Application
• Enter App name: SQLite App
• Enter Project name: android-sqlite
• Pakcage: com.hmkcode.android
• Keep other defualt selections, click Next until you reach Finish

( 2 ) Data Model Design “Table Structure”

We want to create the following:

• One Database instance: “BookDB“.
• One Table: “books” with three columns id, title & author
• 

 

( 3 ) Object Model “Book.java”

• Create one Java bean class: Book.java

• /src/com/hmkcode/android/model/Book.java

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package com.hmkcode.android.model; 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;     }     //getters & setters     @Override     public String toString() {         return "Book [id=" + id + ", title=" + title + ", author=" + author                 + "]";     } }

( 4 ) extends SQLiteOpenHelper

The recommended method to create a new SQLite database is to create a subclass of SQLiteOpenHelper and override the onCreate() method, in which you can execute a SQLite command to create tables in the database.

This is the main step.

• Create a new class MySQLiteHelper extends SQLiteOpenHelper.
• MySQLiteHelper constructor must call the super class constructor.
• Override onCreate() method to create the table(s)
• Override onUpgrade() to drop old tables and create new ones.

• /src/com/hmkcode/android/sqlite/MySQLiteHelper.java

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package com.hmkcode.android.sqlite; import android.content.Context; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; 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);     } }

• This class MySQLiteHelper will just create for us Database “BookDB” with one empty table “books“.
• Next, we will create methods to help us populate “insert”, read “select”, update and delete book(s) from this table.

( 5 ) Add, Get, Update & Delete a Book

• In the same file “MySQLiteHelper.java” we will add 5 methods

1. addBook(Book book)
2. getBook(int id)
3. getAllBooks()
4. update(Book book)
5. delete(Book book)

• Some static constants 

Define static constants for table & columns names;

    // 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};

1. addBook(Book book)

Notice:

• ConentValues this class is used to store a set of values.
• Log.d() just for logging, so we can see the result later on LogCat when we run the App.

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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();     }

2. getBook(int id)

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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; }

3. getAllBooks()

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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;    }

4. update(Book book)

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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; }

5. delete(Book book)

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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());     }

Complete MySQLiteHelper.java Code:

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package com.hmkcode.android.sqlite; import java.util.LinkedList; import java.util.List; import com.hmkcode.android.model.Book; 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){         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.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,                 KEY_ID+" = ?",                 new String[] { String.valueOf(book.getId()) });         // 3. close         db.close();         Log.d("deleteBook", book.toString());     } }

( 6 ) Using MySQLiteHelper in Activity

• /src/com/hmkcode/android/MainActivity.java

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package com.hmkcode.android; import java.util.List; import com.hmkcode.android.model.Book; import com.hmkcode.android.sqlite.MySQLiteHelper; import android.os.Bundle; import android.app.Activity; public class MainActivity extends Activity {     @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);         MySQLiteHelper db = new MySQLiteHelper(this);         /**          * CRUD Operations          * */         // 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();     } }

• Deploy the App on the emulator and run it.
• Look for the results in LogCat!

( 7 ) Where to See the Results? LogCat!

• Log function Log.d() used within the addBook(), getBook()…etc. will log database operations on LogCat Eclipse (ADT) window.

• If you don’t see LogCat window, you need to add it.
• go to Window >> Show View >> Others… (on Show View window) Android >> LogCat

 

LogCat view

 

转自http://hmkcode.com/android-simple-sqlite-database-tutorial/