java - 创建和使用数据库 : Android

Question

我正在开发一个应用程序，它有几个模块。 我将不得不多次访问许多模块中的同一个数据库。

我的问题是哪个地方是为其创建数据库和表的最佳方式和最佳位置？？

喜欢...

    1. creating the required databases and tables at once while loading app or

    2. Creating db and tables in respective modules when required??
     resulting in extra lines of codes to check if db and table already 
     exists or not..

哪个是好的选择？？或者还有其他更好的方法吗？

如有任何建议，我们将不胜感激。

提前致谢:)

Answer 1

首先你应该创建一个类来创建一个数据库，比如:

package com.DB;

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.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import android.webkit.WebChromeClient.CustomViewCallback;

public class DatabaseHandler_Dashboard extends SQLiteOpenHelper {

    // All Static variables
    // Database Version
    private static final int DATABASE_VERSION = 1;

    // Database Name
    private static final String DATABASE_NAME = "dashboard";

    // Contacts table name
    private static final String TABLE_NAME = "tbl_dashboard";

    // Contacts Table Columns names
    private static final String KEY_ID = "id";
    private static final String RANK = "RANK";
    private static final String MHBHUBCD = "MHBHUBCD";
    private static final String WK1Dkts = "WK1Dkts";
    private static final String WK1Per = "WK1Per";
    private static final String WK1OnTime = "WK1OnTime";

    private static final String WK2Dkts = "WK2Dkts";    
    private static final String Wk2Per = "Wk2Per";
    private static final String WK2OnTime = "WK2OnTime";

    private static final String QTDDkts = "QTDDkts";
    private static final String QTDPer = "QTDPer";
    private static final String QTDOnTime = "QTDOnTime";

    private static final String YTDDkts = "YTDDkts";
    private static final String YTDPer = "YTDPer";
    private static final String YTDOnTime = "YTDOnTime";



    public DatabaseHandler_Dashboard(Context context) {
        // TODO Auto-generated constructor stub
        super(context, DATABASE_NAME, null, DATABASE_VERSION);  
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub

        String CREATE_DEVICE_TABLE = "CREATE TABLE " + TABLE_NAME + "("
        + RANK + " TEXT,"
        + MHBHUBCD + " TEXT,"
        + WK1Dkts + " TEXT,"
        + WK1Per + " TEXT,"
        + WK1OnTime + " TEXT,"

        + WK2Dkts + " TEXT,"
        + Wk2Per + " TEXT,"
        + WK2OnTime + " TEXT,"

        + QTDDkts + " TEXT,"
        + QTDPer + " TEXT,"
        + QTDOnTime + " TEXT,"

        + YTDDkts + " TEXT,"
        + YTDPer + " TEXT,"
        + YTDOnTime + " TEXT"
        + ")";
        db.execSQL(CREATE_DEVICE_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub

        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);

        // Create tables again
        onCreate(db);
    }

    /**
     * All CRUD(Create, Read, Update, Delete) Operations
     */

    // Adding new Device
    public void addDevice(Contact_Dashboard device) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();

        values.put(RANK , device.get_RANK());

        values.put(MHBHUBCD  , device.get_MHBHUBCD ()); 

        values.put(WK1Dkts  , device.get_WK1Dkts()); 
        values.put(WK1Per  , device.get_WK1Per()); 
        values.put(WK1OnTime  , device.get_WK1OnTime()); 

        values.put(WK2Dkts  , device.get_WK2Dkts()); 
        values.put(Wk2Per   , device.get_Wk2Per()); 
        values.put(WK2OnTime  , device.get_WK2OnTime()); 

        values.put(QTDDkts  , device.get_QTDDkts()); 
        values.put(QTDPer  , device.get_QTDPer()); 
        values.put(QTDOnTime  , device.get_QTDOnTime()); 

        values.put(YTDDkts   , device.get_YTDDkts()); 
        values.put(YTDPer   , device.get_YTDPer()); 
        values.put(YTDOnTime   , device.get_YTDOnTime()); 


        // Inserting Row
        db.insert(TABLE_NAME, null, values);

        db.close(); // Closing database connection
    }





    // Getting All Devices
    public List<Contact_Dashboard> getAllDevice() {
        List<Contact_Dashboard> deviceList = new ArrayList<Contact_Dashboard>();
        // Select All Query
        String selectQuery = "SELECT  * FROM " + TABLE_NAME;

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

        // looping through all rows and adding to list
        if (cursor !=null)
        {
            if (cursor.moveToFirst()) {
                do {
                    Contact_Dashboard device = new Contact_Dashboard();

                    device.set_RANK(cursor.getString(0));
                    device.set_MHBHUBCD(cursor.getString(1));

                    device.set_WK1Dkts(cursor.getString(2));
                    device.set_WK1Per (cursor.getString(3));
                    device.set_WK1OnTime (cursor.getString(4));


                    device.set_WK2Dkts (cursor.getString(5));
                    device.set_Wk2Per  (cursor.getString(6));
                    device.set_WK2OnTime (cursor.getString(7));

                    device.set_QTDDkts (cursor.getString(8));
                    device.set_QTDPer (cursor.getString(9));
                    device.set_QTDOnTime (cursor.getString(10));


                    device.set_YTDDkts (cursor.getString(11));
                    device.set_YTDPer (cursor.getString(12));
                    device.set_YTDOnTime (cursor.getString(13));


                    // Adding Device to list
                    deviceList.add(device);

                } while (cursor.moveToNext());

            }

    }
        cursor.close();
        return deviceList;


}





    // Getting contacts Count
    public int get_all_data() {
        String countQuery = "SELECT  * FROM " + TABLE_NAME;
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(countQuery, null);
        cursor.close();

        // return count
        return cursor.getCount();
    }



    public int del_all_data()
    {
        SQLiteDatabase db = this.getWritableDatabase();
         return db.delete(TABLE_NAME, null, null);

    }



    // Getting All Devices
    public List<Contact_Dashboard> getAllDevice_sort_by(String vall,String sort_type)
    {
        List<Contact_Dashboard> deviceList = new ArrayList<Contact_Dashboard>();
        // Select All Query
        String selectQuery = "SELECT  * FROM " + TABLE_NAME  + " order by CAST(" + vall + " as integer)" + sort_type;

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

        // looping through all rows and adding to list
        if (cursor !=null)
        {
            if (cursor.moveToFirst()) {
                do {
                    Contact_Dashboard device = new Contact_Dashboard();

                    device.set_RANK(cursor.getString(0));
                    device.set_MHBHUBCD(cursor.getString(1));

                    device.set_WK1Dkts(cursor.getString(2));
                    device.set_WK1Per (cursor.getString(3));
                    device.set_WK1OnTime (cursor.getString(4));


                    device.set_WK2Dkts (cursor.getString(5));
                    device.set_Wk2Per  (cursor.getString(6));
                    device.set_WK2OnTime (cursor.getString(7));

                    device.set_QTDDkts (cursor.getString(8));
                    device.set_QTDPer (cursor.getString(9));
                    device.set_QTDOnTime (cursor.getString(10));


                    device.set_YTDDkts (cursor.getString(11));
                    device.set_YTDPer (cursor.getString(12));
                    device.set_YTDOnTime (cursor.getString(13));


                    // Adding Device to list
                    deviceList.add(device);

                } while (cursor.moveToNext());

            }

    }
        cursor.close();
        return deviceList;


}


}

现在在您的其他 Activity 页面中创建此类的对象，例如:

DatabaseHandler_Dashboard ECDS_DB = new DatabaseHandler_Dashboard(this);

当该 Activity 运行时，它会自动生成您的数据库并检查数据库是否存在....

现在您可以为您的变量创建一个 get set 方法并在每个 Activity 中使用 DB 类对象，例如:

ECDS_DB.del_all_data();

    ECDS_DB.addDevice(new Contact_Dashboard(
                        ARR_RANK[i] ,
                        ARR_MHBHUBCD[i] , 

                        ARR_WK1Dkts[i] ,
                        ARR_WK1OnTime[i] ,
                        ARR_WK1Per[i] ,

                        ARR_WK2Dkts[i] ,
                        ARR_WK2OnTime[i] ,
                        ARR_Wk2Per[i] , 

                        ARR_QTDDkts[i] , 
                        ARR_QTDOnTime[i] ,
                        ARR_QTDPer[i] ,

                        ARR_YTDDkts[i] ,
                        ARR_YTDOnTime[i] ,
                        ARR_YTDPer[i] ));

试试这个，别忘了评论我......................