如何在android中创建数据库? [英] How do I create a database in android?

问题描述

我需要一个在 Android 中创建数据库的分步过程.

I need a step by step procedure for creating a database in Android.

推荐答案

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

Database is important thing in programming. Many of our codes always use data to be processed and saved. Just like any other programming environment, Android supports database programming too. You can use the default database supported by android, SQLiteDatabase.

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

Database in SQLiteDatabase can contain more than one table.Assume that we have one database PERSONALDB and one table BIODATA. The structure of BIODATA is:

_id integer
code string
name string
gender string

_id is for key increment,

code、name和gender是对person的描述.

第一次调用程序时，我们要确保数据库和表是打开的，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 Android 记事本示例 的示例，这里是用于操作表 Biodata 的类 PersonDbHelper.

When program is called for the first time, we have to make sure that the database and the table is opened, if it exists.If not, then we have to create a database and a table. As an example from Android notepad sample, here is the class PersonDbHelper for manipulating table 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;
        }
    }
}

在方法 onCreate 中，您只需要输入下面给出的单个命令来初始化数据库:...

In the method onCreate, you just have to put a single command given below to initialize the database : ...

Db = new PersonDbHelper(this);

...

它会先尝试打开'PersonalDB'.如果它不存在，那么它会创建一个数据库.在这个PersonDbHelper"类中，您有插入、删除、更新、查询表的方法.

It will try to open 'PersonalDB' first.If it does not exist, then it will create a database. In this 'PersonDbHelper' class, you have methods for inserting, deleting, updating, querying the table.

这里是对上述教程的参考:

创建我的第一个安卓数据库

您也可以通过:

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

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

希望这会有所帮助.

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