如何在android中创建数据库？

Question

我需要一步一步的步骤来在Android中创建数据库.

Answer 1

数据库在编程中很重要.我们的许多代码总是使用数据进行处理和保存.就像任何其他编程环境一样,Android也支持数据库编程.您可以使用android支持的默认数据库SQLiteDatabase.

SQLiteDatabase中的数据库可以包含多个PERSONALDB表BIODATA.假设我们有一个数据库和一个表.结构BIODATA是:

_id integer
code string
name string
gender string

_id is for key increment,

code,name和gender,用于描述person.

当第一次调用程序时,我们必须确保打开数据库和表(如果存在).如果不存在,那么我们必须创建一个数据库和一个表.作为一个例子Android notepad sample,这里是PersonDbHelper操作表的类Biodata.

import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;

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

public class PersonDbHelper {
    class Row extends Object {
        public long _Id;
        public String code;
        public String name;
        public String gender;
    }

    private static final String DATABASE_CREATE =
        "create table BIODATA(_id integer primary key autoincrement, "
            + "code text not null,"
            + "name text not null"
            +");";

    private static final String DATABASE_NAME = "PERSONALDB";

    private static final String DATABASE_TABLE = "BIODATA";

    private static final int DATABASE_VERSION = 1;

    private SQLiteDatabase db;

    public PersonDbHelper(Context ctx) {
        try {
            db = ctx.openDatabase(DATABASE_NAME, null);
        } catch (FileNotFoundException e) {
            try {
                db =
                    ctx.createDatabase(DATABASE_NAME, DATABASE_VERSION, 0,
                        null);
                db.execSQL(DATABASE_CREATE);
            } catch (FileNotFoundException e1) {
                db = null;
            }
        }
    }

    public void close() {
        db.close();
    }

    public void createRow(String code, String name) {
        ContentValues initialValues = new ContentValues();
        initialValues.put("code", code);
        initialValues.put("name", name);
        db.insert(DATABASE_TABLE, null, initialValues);
    }

    public void deleteRow(long rowId) {
        db.delete(DATABASE_TABLE, "_id=" + rowId, null);
    }

    public List<Row> fetchAllRows() {
        ArrayList<Row> ret = new ArrayList<Row>();
        try {
            Cursor c =
                db.query(DATABASE_TABLE, new String[] {
                    "_id", "code", "name"}, null, null, null, null, null);
            int numRows = c.count();
            c.first();
            for (int i = 0; i < numRows; ++i) {
                Row row = new Row();
                row._Id = c.getLong(0);
                row.code = c.getString(1);
                row.name = c.getString(2);
                ret.add(row);
                c.next();
            }
        } catch (SQLException e) {
            Log.e("Exception on query", e.toString());
        }
        return ret;
    }

    public Row fetchRow(long rowId) {
        Row row = new Row();
        Cursor c =
            db.query(true, DATABASE_TABLE, new String[] {
                "_id", "code", "name"}, "_id=" + rowId, null, null,
                null, null);
        if (c.count() > 0) {
            c.first();
            row._Id = c.getLong(0);
            row.code = c.getString(1);
            row.name = c.getString(2);
            return row;
        } else {
            row.rowId = -1;
            row.code = row.name= null;
        }
        return row;
    }

    public void updateRow(long rowId, String code, String name) {
        ContentValues args = new ContentValues();
        args.put("code", code);
        args.put("name", name);
        db.update(DATABASE_TABLE, args, "_id=" + rowId, null);
    }
    public Cursor GetAllRows() {
        try {
            return db.query(DATABASE_TABLE, new String[] {
                    "_id", "code", "name"}, null, null, null, null, null);
        } catch (SQLException e) {
            Log.e("Exception on query", e.toString());
            return null;
        }
    }
}

在该方法中onCreate,您只需要在下面给出一个命令来初始化数据库:...

Db = new PersonDbHelper(this);

...

它将首先尝试打开'PersonalDB'.如果它不存在,那么它将创建一个数据库.在这个'PersonDbHelper'类中,您可以使用插入,删除,更新,查询表的方法.

以下是上面教程的参考:

创建我的第一个android数据库

你也可以通过:

http://www.devx.com/wireless/Article/40842

http://www.vogella.de/articles/AndroidSQLite/article.html

希望这可以帮助.

Answer 2

创建数据库:

db= this.openOrCreateDatabase("db_hw3", MODE_PRIVATE, null);