android - 是什么触发了 SqliteDbOpenHelper onUpgrade()？

Question

有人能解释一下如何在 SqliteDbOpenHelper 类中调用 onUpgrade 函数吗？我正在打开我的数据库，但它没有调用 onUpgrade，即使我已经更改了 DB_VERSION。

见以下代码:

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

    static final String DB_NAME = "caddata.sqlite";
    static final int DB_VERSION = 4;

    private static String DB_PATH = "";
    private Context myContext;
    private SQLiteDatabase myDataBase;

    public DbHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
        this.myContext = context;

        DB_PATH = "/data/data/"
                + context.getApplicationContext().getPackageName()
                + "/databases/";            
    }

    public DbHelper open() throws SQLException {        
        myDataBase =  getWritableDatabase();

        Log.d(TAG, "DbHelper Opening Version: " +  this.myDataBase.getVersion());
        return this;
    }

    @Override
    public synchronized void close() {

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

        super.close();

    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        Log.d(TAG, "onCreate called");

        try {           
            createDataBase();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        if ( newVersion > oldVersion)
        {
            Log.d(TAG, "New database version exists for upgrade.");         
            try {
                Log.d(TAG, "Copying database...");
                copyDataBase();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }       
        }
    }

    public void createDataBase() throws IOException {

        boolean dbExist = checkDataBase();

        if (!dbExist) {         

            try {
                copyDataBase();
            } catch (IOException e) {
                throw new Error("Error copying database");
            }
        }

        openDataBaseForRead();
    }


    private boolean checkDataBase() {

        SQLiteDatabase checkDB = null;

        try {
            String myPath = DB_PATH + DB_NAME;
            checkDB = SQLiteDatabase.openDatabase(myPath, null,
                    SQLiteDatabase.OPEN_READONLY
                            | SQLiteDatabase.NO_LOCALIZED_COLLATORS);
            Log.d(TAG, "db exists");
        } catch (SQLiteException e) {
            // database does't exist yet.
            Log.d(TAG, "db doesn't exist");

        }

        if (checkDB != null) {
            checkDB.close();            
        }

        return checkDB != null ? true : false;
    }


    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();

        myDataBase.setVersion(DB_VERSION);
    }

    public void openDataBaseForRead() throws SQLException {

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

    public void openDataBaseForWrite() throws SQLException {

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


}

另请参阅此处详细说明我的问题:Why is onUpgrade() not being invoked on Android sqlite database?我没有得到回复。

我的主要 Activity 从助手打开数据库。我假设只要打开数据库就会调用 onUpgrade() 函数:

@Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        DbHelper myDbHelper =  new DbHelper(this);

        try {

            myDbHelper.createDataBase();

        } catch (IOException ioe) {

            throw new Error("Unable to create database");

        }

        try {

            myDbHelper.openDataBaseForRead();

        }catch(SQLException sqle){

            throw sqle;

        }
}

Answer 1

在我看来，onCreate() 和 onUpgrade() 函数仅在您使用 SQLiteOpenHelper 打开数据库时起作用 。这意味着你应该调用函数getWritableDatabase()或getReadbleDatabase()来打开数据库，然后它也许可以正常工作。