Question

我正在移动设备上直接开发，我有一些问题希望能帮助我澄清使用数据库的开发：

我的应用程序是使用SQLite数据库（只读模式），所以我想要知道我应该在pc上创建.sqlite文件的位置订购应用程序甚至可以直接阅读。
稍后，应用程序应该从a下载db文件集中服务器。因此，我们的想法是继续将该文件放入相同的位置，一个应用程序肯定会知道，并可以检查它是否在尝试使用它之前就存在了。

谢谢！

Answer 1

您需要将SQLite数据库打包为您的应用程序的资源（例如res / raw）或资产。但是，您将无法直接使用打包的SQLite数据库。您需要将其复制到Android期望您的应用程序的数据库文件所在的位置，然后从那里使用它。执行此操作的最佳方法是使用Context.getDatabasePath(String)（传递数据库文件的名称）来确定文件路径。这也是您应该在运行时放置应用程序下载的数据库文件的位置。

Answer 2

您需要将数据库文件复制到assets文件夹中，然后使用以下代码将其写入内存以便在应用程序中访问：

public class DataBaseHelper extends SQLiteOpenHelper{

private static final String TAG = "DataBaseHelper";

//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/" + Constants.package_name + "/databases/";

private static String DB_NAME = "YourDatabaseName.db";

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 doesn't
 */
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 does't 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);

    // 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) {

}

希望这有帮助。

Answer 3

我将我的初始数据库放在'assets'目录中，然后将其复制到用户可访问的路径上 - 如外部存储器（sdcard等）。我用这种方式没有任何麻烦：）

Answer 4

我建议你是否要插入数据而不是仅仅取值你可以在应用程序中创建数据库

总是有路径

像

/数据/数据/ your_project_name /数据库/ yourdatabase_name

http://www.anotherandroidblog.com/2010/08/04/android-database-tutorial/

在Android应用程序中放置sqlite文件的位置

4 个答案: