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我正在使用这个DataBaseHelper.class，并卡在onUpgrade（） - 方法上。我不知道如何弄清楚数据库的版本号是什么。我可以将版本设置为1，第一次发布它，当我发布更新时，我可以将版本设置为2 (myDataBase.setVersion(2);)。但只要应用程序运行，它只会是2。下次启动时，它又是1。 private static int DATABASE_VERSION也是如此。我正在考虑将版本号存储在额外的表格中，但在我看来，这似乎不是最佳实践。onUpgrade数据库 - oldVersion - newVersion
那么如何确保版本号在升级后增加并保持不变（值分配为private static int DATABASE_VERSION或myDataBase.getVersion();）？
的DataBaseHelper级：
public class DataBaseHelper extends SQLiteOpenHelper {
//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/com.mydatabase.db/databases/";
private static String DB_NAME = "database.sl3";
private SQLiteDatabase myDataBase;
private final Context myContext;
// Do you need this?
private static int DATABASE_VERSION = 2;
// or is this correct:
// private static int DATABASE_VERSION = myDataBase.getVersion();
/**
* 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, DATABASE_VERSION);
this.myContext = context;
}
/**
* Creates an empty database on the system and rewrites it with your own
* database.
* */
public void
createDataBase() throws IOException {
boolean dbExist = checkDataBase();
if (dbExist) {
}
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[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);
// Which parameters do I have to pass?
onUpgrade(myDataBase, DATABASE_VERSION, 2);
}
@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) {
Log.d ("onUpgrade first log", Integer.toString(myDataBase.getVersion()));
if (oldVersion == 1) {
// do something
// And then do this!?
DATABASE_VERSION = 2;
// or do this
myDataBase.setVersion(2);
Log.d ("onUpgrade sedond log", Integer.toString(myDataBase.getVersion()));
}
else {
Log.d("onUpgrade", "else-clause: Already upgraded!");
}
}
嗨格雷厄姆Borland的！你是对的，我从资产文件夹中导入一个现有的数据库，我想这就是我需要的东西，直接把它应用到assets中的数据库文件！但我该怎么做？ – BenjaminButton
用_it_表示版本号。 – BenjaminButton
我懂了！在createDataBase类中缺少一行： 'public void createDataBase（）throws IOException {boolean dbExist = checkDataBase（）; if（dbExist）{/ *这行：*/this.getWritableDatabase（）;} ...' 此外onUpgrade（）在创建类DataBaseHelper的新对象时调用**但只有在数据库版本号不匹配。所以这意味着没有必要自己调用升级。如果您发布数据库的更新，只需将版本号增加1，然后在onUpgrade（）方法中应用更改。希望能帮助任何人！ – BenjaminButton