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我是Android SQLite的新手。這是我的：資產文件夾中的DB文件。它會被更新嗎？
- 我在我的
assets文件夾中有db.sqlite。 - db的意圖是隻讀。用戶不會寫信給它。
- 當應用程序得到更新時，
db.sqlite將被替換爲新的數據庫（我將從項目中刪除舊文件並添加新的數據庫）。
什麼，我關心的是：
- 將舊數據庫文件被刪除？ （這是我想要的;用新的替換舊的）
- 爲什麼問？因爲當我調試我的應用程序時，每次更新db文件時，我都需要從設備上卸載應用程序才能強制更新。當用戶從Play商店更新我的應用時，用戶是否也需要這樣做？我很害怕。
- 這會受到我執行onCreate(SQLiteDatabase)和onUpgrade(SQLiteDatabase, int, int)的影響嗎？
- 如果是，那麼實施它們以符合我的要求的正確方法是什麼？
這是我如何擴展SQLiteOpenHelper類。我也跟着教程中，我在互聯網上找到：
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
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{
//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/com.mydomain.myapp/databases/";
private static String DB_NAME = "db.sqlite";
private 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
Log.i("myapp", "database already exist");
}else{
Log.i("myapp", "database NOT exist");
//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.getReadableDatabase();
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){
//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[1024];
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) {
}
// My public helper methods to access and get content from the database go here
您的代碼比我的要簡單得多。我希望它能起作用。儘管在測試它之前我有一個問題：在'initialize（）'中，如果存在並且版本不同，則只刪除舊的db。你不想創造一個新的？ – iTurki 2012-07-22 19:33:13
它後面有「if（！databaseExists（））{createDatabase（）;}」。它創建數據庫，如果它被刪除。當然可以重寫保存此檢查。 – biegleux 2012-07-22 19:41:46
我沒有注意到這一點。認爲這是一個「其他」部分！我想你的實施將起作用。謝謝:) – iTurki 2012-07-23 17:52:13