Question

我有一个sqlite数据库存储在“assets”文件夹中，我想将其存储在Android设备的/ data / data文件夹中。它只是一个只读数据库，我想从中检索数据。

我一直在阅读很多讨论这个问题的话题但是当我检查设备中的/ data / data /文件夹时，我的包不在那里。这是我一直在使用的代码：

public class DatabaseManager extends SQLiteOpenHelper {
private static final String TAG = "DataBaseManager";

private static String DB_PATH = "/data/data/com.my_package/databases/";
private static String DB_NAME = "my_database";
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 DatabaseManager(Context context) {

    super(context, DB_NAME, null, 1);
    this.myContext = context;
    try {
        createDataBase();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

/**
 * 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
        Log.d("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_READONLY);
    }catch(SQLiteException e){
        Log.d("DATABASE", "DOESNT EXIST");
    }

    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();
    Log.d("COPY DATABASE", "DATABASE COPIED");
}

public void openDataBase() throws SQLException {
    //Open the database
    String myPath = DB_PATH + DB_NAME;
    myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
    Cursor cursor = myDataBase.rawQuery("SELECT * FROM chapters", null);

    while (cursor.moveToNext()) {
        cursor.getString(3);
        Log.d("CONTENT", cursor.getString(3));
    }

    myDataBase.beginTransaction();
}

@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) {

}

感谢Log.d（）消息，我可以看到以下消息：“database already exists”（来自createDatabase方法的消息）但是，我的Android设备的/ data / data文件夹中没有数据。

这对我来说很奇怪，因为在checkDatabase方法中，我检查myPath变量中是否存在数据库，其值对应于DB_PATH和DB_NAME的变量，即/ data / data文件夹，就像我说的那样，我打开了内部存储器我的设备，并检查是否在/ data / data文件夹中创建了什么，但没有。

Answer 1

最好检查一下DB File

 public boolean checkDataBase(){
    File databaseFile = new File(DB_PATH + DB_NAME);
    return databaseFile.exists();        
}

Answer 2

如果数据库不存在，

SQLiteDatabase.openDatabase将自动创建数据库（请参阅CREATE_IF_NECESSARY标志）。

通常，您必须先将嵌入式数据库从asset目录复制到应用程序数据目录：data/data/com.my_package/databases。

然后你可以使用你的数据库。

如有必要，请参阅SQLiteAssetHelper：https://stackoverflow.com/a/920523/998096

Answer 3

我认为您要从＆＃34; my_database＆＃34;更改DB_NAME变量。到＆＃34; my_database.sqlite＆＃34;

并且您无法在内部存储器中看到您的数据库... bcoz数据库将仅保存到系统文件夹... 如果你想检查它你可能需要一个root的Android设备或你可以检查使用android studio ...

检查此链接... check database if exist in android studio

/ data / data Android

3 个答案: