android - 如何创建 Android 数据库应用程序？

Question

我是数据库的新手，不知道这是否是实现我想要实现的目标的最佳方式。我想为我周围的餐馆创建一个自定义列表，然后搜索它们，并根据排名、标题或位置对它们进行排序。

我需要为此创建一个数据库吗？从技术上讲，我可以使用文本文件和数组，但我觉得这样效率很低。我需要一个节点来包含以下数据:机构名称、地址、电话号码、排名(基于我们的排名系统)。

我应该怎么做？

Answer 1

是的，您肯定想使用数据库。如果您使用手机本地的数据库，则需要使用 SQLite 数据库。 Here是一个很好的起点。

如果你想要一个预装在手机中的数据库，把它放在你的 Assets 文件夹中。下面是一个数据库助手类的示例，其中的数据库随手机一起打包:

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.text.DateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Vector;


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

public class DataBaseHelper extends SQLiteOpenHelper{

private static final String TAG = "DataBaseHelper";

//The Androids default system path of your application database.
private static String DB_PATH = "/data/data/yourpackage/databases/";

private static String DB_NAME = "DatabaseName";

public SQLiteDatabase myDataBase; 

private final Context myContext;


    /**
     * Constructor
     * Takes and keeps a reference of the passed context in order to access to the application assets and resources.
     * @param context
     */
    public DataBaseHelper(Context context) {

        super(context, DB_NAME, null, 1);
        this.myContext = context;
    }   

  /**
     * Creates a empty database on the system and rewrites it with your own database.
     * */
    public void createDataBase() throws IOException{

        boolean dbExist = checkDataBase();

        if(dbExist){
            //do nothing - database already exist
        }else{

            //By calling this method and empty database will be created into the default system path
               //of your application so we are gonna be able to overwrite that database with our database.
            this.getWritableDatabase();

            try {

                copyDataBase();

            } catch (IOException e) {

                throw new Error("Error copying database");

            }
        }

    }

    /**
     * Check if the database already exist to avoid re-copying the file each time you open the application.
     * @return true if it exists, false if it doesnt
     */
    private boolean checkDataBase(){

        SQLiteDatabase checkDB = null;

        try{
            String myPath = DB_PATH + DB_NAME;
            checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);

        }catch(SQLiteException e){

            //database doest exist yet.

        }

        if(checkDB != null){

            checkDB.close();

        }

        return checkDB != null ? true : false;
    }

    /**
     * Copies your database from your local assets-folder to the just created empty database in the
     * system folder, from where it can be accessed and handled.
     * This is done by transfering bytestream.
     * */
    private void copyDataBase() throws IOException{



        //Open your local db as the input stream
        InputStream myInput = myContext.getAssets().open(DB_NAME);

        Log.d(TAG, "found the database");
        // Path to the just created empty db
        String outFileName = DB_PATH + DB_NAME;


        //Open the empty db as the output stream
        OutputStream myOutput = new FileOutputStream(outFileName);


        //transfer bytes from the inputfile to the outputfile
        byte[] buffer = new byte[2048];
        int length;
        while ((length = myInput.read(buffer))>0){
            myOutput.write(buffer, 0, length);
        }

        //Close the streams
        myOutput.flush();
        myOutput.close();
        myInput.close();

    }

    public void openDataBase() throws SQLException{

        //Open the database
        String myPath = DB_PATH + DB_NAME;
        myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
    }

    @Override
    public synchronized void close() {

            if(myDataBase != null)
                myDataBase.close();

            super.close();

    }

    @Override
    public void onCreate(SQLiteDatabase db) {

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

        // Add your public helper methods to access and get content from the database.
       // You could return cursors by doing "return myDataBase.query(....)" so itd be easy
       // to you to create adapters for your views.