android - Sqlite isOpen() 未在 android 中显示

Question

我有一个数据库，现在我想检查数据库是否打开。所以我正在使用 isOpen() 方法来完成这项任务。但是我看到这个方法不可用，所以我无法使用 isOpen()。我是按照这个链接 IllegalStateException: database already closed (using ViewPager)

这是我的代码：-

mydb db = new mydbthis);
db.close(); // this method is found.
db.isOpen() // this method is not availble.

在我能得到它的地方解决它。

Answer 1

mydb db = new mydbthis);

那是行不通的。

直接使用openOrCreateDatabase()或扩展一个SQLiteOpenHelper.

File dbFile = new File(getFilesDir(),"my_app.db");
SQLiteDatabse db = SQLiteDatabase.openOrCreateDatabase(dbFile,null,null);
Log.i("TEST","DB is open: " + db.isOpen() );

或者：

public class DataHelper extends SQLiteOpenHelper {
    private static final int VERSION = 1;
    private static final String DB_NAME = "myapp.db";

    public DataHelper(Context context) {
        super(context, DB_NAME, null, VERSION);
    }

    public void onCreate(SQLiteDatabase db) {
        db.beginTransaction();

        try {
            db.execSQL("CREATE TABLE my_table( name TEXT, age NUMBER )");
            db.setTransactionSuccessful();
        } finally {
            db.endTransaction();
        }
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int i, int i2) {
      //--nothing for now--
    }
}

从 Activity 类中用作：

DataHelper dh = new DataHelper(this); 
SQLiteDatabase db = dh.getReadableDatabase();
Log.i("TEST","DB is open: " + db.isOpen() );

Answer 2

private static class DatabaseHelper extends SQLiteOpenHelper {

        Context helperContext;

        DatabaseHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
            helperContext = context;
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            Log.w(TAG, "Upgrading database!!!!!");
            //db.execSQL("");
            onCreate(db);
        }

        public void createDataBase() throws IOException {
            boolean dbExist = checkDataBase();
            if (dbExist) {
            } else {

                //make sure your database has this table already created in it
                //this does not actually work here
                /*
                 * db.execSQL("CREATE TABLE IF NOT EXISTS \"android_metadata\" (\"locale\" TEXT DEFAULT 'en_US')"
                 * );
                 * db.execSQL("INSERT INTO \"android_metadata\" VALUES ('en_US')"
                 * );
                 */
                this.getReadableDatabase();
                try {
                    copyDataBase();
                } catch (IOException e) {
                    throw new Error("Error copying database");
                }
            }
        }

        public SQLiteDatabase getDatabase() {
            String myPath = DB_PATH + DATABASE_NAME;
            return SQLiteDatabase.openDatabase(myPath, null,
                    SQLiteDatabase.OPEN_READONLY);
        }

        private boolean checkDataBase() {
            SQLiteDatabase checkDB = null;
            try {
                String myPath = DB_PATH + DATABASE_NAME;
                checkDB = SQLiteDatabase.openDatabase(myPath, null,
                        SQLiteDatabase.OPEN_READONLY);
            } catch (SQLiteException e) {
            }
            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 = helperContext.getAssets().open(DATABASE_NAME);

            // Path to the just created empty db
            String outFileName = DB_PATH + DATABASE_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 + DATABASE_NAME;
            mDb = SQLiteDatabase.openDatabase(myPath, null,
                    SQLiteDatabase.OPEN_READWRITE);
        }

        @Override
        public synchronized void close() {

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

            super.close();

        }
    }