Android数据库的使用

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注：Android中是使用Sqlite数据库的

一、创建数据库

利用继承SQLiteOpenHelper类创建数据库帮助类，由此类创建数据库

public class DbOpenHelper extends SQLiteOpenHelper {    //数据库文件名    public static final String DB_NAME = "contact.db";    //数据库版本    public static final int DB_VERSION=1;    //数据库表的内容    public static final String TABLE_NAME="contactinfo";    public static final String _USERNAME="username";    public static final String _PHONE="phone";    private static final String _ID = "id";    public DbOpenHelper(Context context) {        super(context, DB_NAME, null, DB_VERSION);    }    //数据库文件创建的时候调用该方法    @Override    public void onCreate(SQLiteDatabase db) {        db.execSQL("create table "+TABLE_NAME+" ("+_ID+" integer primary key autoincrement," +                _USERNAME+" text,"+_PHONE+" text);");    }    //数据据更新，只要跟之前的数据库版本不一样，则会调用，该方法可以修改数据库表的各种数据    @Override    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {    }}

注：保存数据库文件：/data/data/包名/databases/xxx.db

二、创建DAO类，对数据库进行增删改查

public class ContactDao {    private DbOpenHelper mHelper;    public ContactDao(Context c ){        mHelper = new DbOpenHelper(c);    }    //增    public void insertContact(String username,String phone){        SQLiteDatabase db = mHelper.getWritableDatabase();        db.execSQL("insert into "+DbOpenHelper.TABLE_NAME                        +"("+DbOpenHelper._USERNAME+","+DbOpenHelper._PHONE+") values(?,?);",                new String[]{username,phone});    }    //删    public void updateContact(String username,String newPhone){        SQLiteDatabase db = mHelper.getWritableDatabase();        db.execSQL("update contactinfo set phone=? where username=?;",                new String[]{newPhone,username});    }    //改    public void deleteContact(String username){        SQLiteDatabase db = mHelper.getWritableDatabase();        db.execSQL("delete from contactinfo where username=?;",                new String[]{username});    }    //查    public String queryContact(String phone){        SQLiteDatabase db = mHelper.getReadableDatabase();        Cursor cursor = db.rawQuery("select username from contactinfo where phone=?;",                new String[]{phone});        while (cursor.moveToNext()) {            String username = cursor.getString(0);            return username;        }    }}

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