Android学习笔记-保存数据到SQL数据库中(Saving Data in SQL Databases)

Contract Class的定义:
    Contract Class，又可以叫做Companion Class。
    Android Developer的帮助文档是这么说的:
   < A contract class is a container for constants that define names for URIs,
     tables, and columns. The contract class allows you to use the same constants
     across all the other classes in the same package. This lets you change a
     column name in one place and have it propagate throughout your code.>
     Contact 类是定义URI、表、列的名字的容器。这个类允许我们在同一包的不同类下使用相同的常量。
     我们在一处修改了列名，同时传播到我们代码的每个地方。

package com.example.sqlitetest;
//Contract类
public class Contact {
   
    int _id;
    String _name;
    String _phone_number;
   
    public Contact(){
       
    }
    public Contact(int id, String name, String _phone_number){
        this._id = id;
        this._name = name;
        this._phone_number = _phone_number;
    }
   
    public Contact(String name, String _phone_number){
        this._name = name;
        this._phone_number = _phone_number;
    }
    public int getID(){
        return this._id;
    }
   
    public void setID(int id){
        this._id = id;
    }
   
    public String getName(){
        return this._name;
    }
   
    public void setName(String name){
        this._name = name;
    }
   
    public String getPhoneNumber(){
        return this._phone_number;
    }

    public void setPhoneNumber(String phone_number){
        this._phone_number = phone_number;
    }
}

SQLiteDatabase db = this.getWritableDatabase();
 
ContentValues values = new ContentValues();
values.put(KEY_NAME, contact.getName());
values.put(KEY_PH_NO, contact.getPhoneNumber());
 
db.insert(TABLE_CONTACTS, null, values);
db.close();

SQLiteDatabase db = this.getWritableDatabase();
db.delete(TABLE_CONTACTS, KEY_ID + " = ?",
        new String[] { String.valueOf(contact.getID()) });
db.close();

 SQLiteDatabase db = this.getWritableDatabase();

ContentValues values = new ContentValues();
values.put(KEY_NAME, contact.getName());
values.put(KEY_PH_NO, contact.getPhoneNumber());

return db.update(TABLE_CONTACTS, values, KEY_ID + " = ?",
          ew String[] { String.valueOf(contact.getID()) });
 

SQLiteDatabase db = this.getReadableDatabase();

Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID,
                KEY_NAME, KEY_PH_NO }, KEY_ID + "=?",
                new String[] { String.valueOf(id) }, null, null, null, null);
if (cursor != null)
cursor.moveToFirst();

Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
                cursor.getString(1), cursor.getString(2));

return contact;

package com.example.sqlitetest;

import java.util.ArrayList;
import java.util.List;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DatabaseHelper extends SQLiteOpenHelper {

    // 数据库版本
    private static final int DATABASE_VERSION = 1;

    // 数据库名
    private static final String DATABASE_NAME = "contactsManager";

    //Contact表名
    private static final String TABLE_CONTACTS = "contacts";

    //Contact表的列名
    private static final String KEY_ID = "id";
    private static final String KEY_NAME = "name";
    private static final String KEY_PH_NO = "phone_number";

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

    // 创建表
    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "("
                + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
                + KEY_PH_NO + " TEXT" + ")";
        db.execSQL(CREATE_CONTACTS_TABLE);
    }

    // 更新表
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // 删除旧表
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);

        //再次创建表
        onCreate(db);
    }

    /**
     *增删改查操作
     */

    // 增加新的联系人
    void addContact(Contact contact) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_NAME, contact.getName());
        values.put(KEY_PH_NO, contact.getPhoneNumber());

        // 插入行
        db.insert(TABLE_CONTACTS, null, values);
        db.close(); // 关闭数据库的连接
    }

    // 获取联系人
    Contact getContact(int id) {
        SQLiteDatabase db = this.getReadableDatabase();

        Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID,
                KEY_NAME, KEY_PH_NO }, KEY_ID + "=?",
                new String[] { String.valueOf(id) }, null, null, null, null);
        if (cursor != null)
            cursor.moveToFirst();

        Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
                cursor.getString(1), cursor.getString(2));
        return contact;
    }
   
    // 获取所有联系人
    public List<Contact> getAllContacts() {
        List<Contact> contactList = new ArrayList<Contact>();
        // Select All Query
        String selectQuery = "SELECT  * FROM " + TABLE_CONTACTS;

        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);

        if (cursor.moveToFirst()) {
            do {
                Contact contact = new Contact();
                contact.setID(Integer.parseInt(cursor.getString(0)));
                contact.setName(cursor.getString(1));
                contact.setPhoneNumber(cursor.getString(2));
                contactList.add(contact);
            } while (cursor.moveToNext());
        }

        return contactList;
    }

    // 更新单个联系人
    public int updateContact(Contact contact) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_NAME, contact.getName());
        values.put(KEY_PH_NO, contact.getPhoneNumber());

        //更新行
        return db.update(TABLE_CONTACTS, values, KEY_ID + " = ?",
                new String[] { String.valueOf(contact.getID()) });
    }

    // 删除单个联系人
    public void deleteContact(Contact contact) {
        SQLiteDatabase db = this.getWritableDatabase();
        db.delete(TABLE_CONTACTS, KEY_ID + " = ?",
                new String[] { String.valueOf(contact.getID()) });
        db.close();
    }

    // 获取联系人数量
    public int getContactsCount() {
        String countQuery = "SELECT  * FROM " + TABLE_CONTACTS;
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(countQuery, null);
        cursor.close();

        return cursor.getCount();
    }
}