Android SQLite 示例 [英] Android SQLite Example

问题描述

我是 Android 新手，我必须创建一个需要使用 SQLite 数据库的应用程序.我不太熟悉 SQLite.

I am new to Android and I have to create an application where I need to use a SQLite database. I am not so well equipped with the SQLite.

能否告诉我SQLiteOpenHelper 类的用途和用途，并提供一个简单的数据库创建和插入示例?

Could you tell me what the purpose and use of the SQLiteOpenHelper class, and provide a simple database creation and insertion example?

推荐答案

Sqlite helper 类帮助我们管理数据库创建和版本管理.SQLiteOpenHelper 负责所有数据库管理活动.要使用它，
1.覆盖SQLiteOpenHelper的onCreate(), onUpgrade()方法.可选择覆盖 onOpen() 方法.
2.使用该子类创建可读或可写的数据库，并使用SQLiteDatabase的四个API方法insert()、execSQL()、update()、delete()来创建、读取、更新和删除表格中的行.

Sqlite helper class helps us to manage database creation and version management. SQLiteOpenHelper takes care of all database management activities. To use it,
1.Override onCreate(), onUpgrade() methods of SQLiteOpenHelper. Optionally override onOpen() method.
2.Use this subclass to create either a readable or writable database and use the SQLiteDatabase's four API methods insert(), execSQL(), update(), delete() to create, read, update and delete rows of your table.

创建 MyEmployees 表并选择和插入记录的示例:

Example to create a MyEmployees table and to select and insert records:

public class MyDatabaseHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME = "DBName";

    private static final int DATABASE_VERSION = 2;

    // Database creation sql statement
    private static final String DATABASE_CREATE = "create table MyEmployees
                                 ( _id integer primary key,name text not null);";

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

    // Method is called during creation of the database
    @Override
    public void onCreate(SQLiteDatabase database) {
        database.execSQL(DATABASE_CREATE);
    }

    // Method is called during an upgrade of the database,
    @Override
    public void onUpgrade(SQLiteDatabase database,int oldVersion,int newVersion){
        Log.w(MyDatabaseHelper.class.getName(),
                         "Upgrading database from version " + oldVersion + " to "
                         + newVersion + ", which will destroy all old data");
        database.execSQL("DROP TABLE IF EXISTS MyEmployees");
        onCreate(database);
    }
}

现在你可以使用这个类了，

Now you can use this class as below,

public class MyDB{  

    private MyDatabaseHelper dbHelper;  

    private SQLiteDatabase database;  

    public final static String EMP_TABLE="MyEmployees"; // name of table 

    public final static String EMP_ID="_id"; // id value for employee
    public final static String EMP_NAME="name";  // name of employee

    /** 
     * 
     * @param context 
     */  
    public MyDB(Context context){  
        dbHelper = new MyDatabaseHelper(context);  
        database = dbHelper.getWritableDatabase();  
    }


    public long createRecords(String id, String name){  
        ContentValues values = new ContentValues();  
        values.put(EMP_ID, id);  
        values.put(EMP_NAME, name);  
        return database.insert(EMP_TABLE, null, values);  
    }    

    public Cursor selectRecords() {
        String[] cols = new String[] {EMP_ID, EMP_NAME};  
        Cursor mCursor = database.query(true, EMP_TABLE,cols,null  
            , null, null, null, null, null);  
        if (mCursor != null) {  
            mCursor.moveToFirst();  
        }  
        return mCursor; // iterate to get each value.
    }
}

现在您可以在您的活动中使用 MyDB 类来进行所有数据库操作.创建记录将帮助您插入值，同样您可以拥有自己的更新和删除功能.

Now you can use MyDB class in you activity to have all the database operations. The create records will help you to insert the values similarly you can have your own functions for update and delete.

这篇关于Android SQLite 示例的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！