如何清除一个SQLite数据库中的每个我开始我的应用程序的时间？ [英] How can I clear an SQLite database each time I start my application?

问题描述

我希望我的SQLite数据库实例擦干程序启动时。

I want my SQLite database instance to be wiped away when the program starts.

我想是在我的课MyDBAdapter.java这样做的方法：

What I tried was make a method on my class MyDBAdapter.java like this:

public class MyDbAdapter {
    private static final String TAG = "NotesDbAdapter";
    private DatabaseHelper mDbHelper;
    private SQLiteDatabase mDb;
    private static final String DATABASE_NAME = "gpslocdb";
    private static final String PERMISSION_TABLE_CREATE = "CREATE TABLE permission ( fk_email1 varchar, fk_email2 varchar, validated tinyint, hour1 time default '08:00:00', hour2 time default '20:00:00', date1 date, date2 date, weekend tinyint default '0', fk_type varchar, PRIMARY KEY  (fk_email1,fk_email2))";
    private static final String USER_TABLE_CREATE = "CREATE TABLE user ( email varchar, password varchar, fullName varchar, mobilePhone varchar, mobileOperatingSystem varchar, PRIMARY KEY  (email))";

    private static final int DATABASE_VERSION = 2;
    private final Context mCtx;
    private static class DatabaseHelper extends SQLiteOpenHelper {

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

        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL(PERMISSION_TABLE_CREATE);
            db.execSQL(USER_TABLE_CREATE);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            db.execSQL("DROP TABLE IF EXISTS user");
            db.execSQL("DROP TABLE IF EXISTS permission");
            onCreate(db);
        }
    }

    /**
     * Constructor - takes the context to allow the database to be
     * opened/created
     * 
     * @param ctx the Context within which to work
     */
    public MyDbAdapter(Context ctx) {
        this.mCtx = ctx;
    }

    /**
     * Open the database. If it cannot be opened, try to create a new
     * instance of the database. If it cannot be created, throw an exception to
     * signal the failure
     * 
     * @return this (self reference, allowing this to be chained in an
     *         initialization call)
     * @throws SQLException if the database could be neither opened or created
     */
    public MyDbAdapter open() throws SQLException {
        mDbHelper = new DatabaseHelper(mCtx);
        mDb = mDbHelper.getWritableDatabase();
        return this;
    }

    public void close() {
        mDbHelper.close();
    }

    public long createUser(String email, String password, String fullName, String mobilePhone, String mobileOperatingSystem) 
    {
        ContentValues initialValues = new ContentValues();
        initialValues.put("email",email);
        initialValues.put("password",password);
        initialValues.put("fullName",fullName);
        initialValues.put("mobilePhone",mobilePhone);
        initialValues.put("mobileOperatingSystem",mobileOperatingSystem);
        return mDb.insert("user", null, initialValues);
    }


    public Cursor fetchAllUsers() {

        return mDb.query("user", new String[] {"email", "password", "fullName", "mobilePhone", "mobileOperatingSystem"}, null, null, null, null, null);
    }

    public Cursor fetchUser(String email) throws SQLException {

        Cursor mCursor = mDb.query(true, "user", new String[] {"email", "password", "fullName", "mobilePhone", "mobileOperatingSystem"}
            , "email" + "=" + email, null, null, null, null, null);
        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;
    }
    public List<Friend> retrieveAllUsers() 
    {
        List <Friend> friends=new ArrayList<Friend>();

        Cursor result=fetchAllUsers();

        if( result.moveToFirst() ){
            do{
                //note.getString(note.getColumnIndexOrThrow(NotesDbAdapter.KEY_TITLE)));
                friends.add(new Friend(result.getString(result.getColumnIndexOrThrow("email")), "","","",""));
            }while( result.moveToNext() );
        }


        return friends;
    }

}

什么是做到这一点的最好方法是什么？

What is the best way to do this?

推荐答案

除了的onCreate（）和 onUpgrade（）你可以覆盖的OnOpen（）。删除所有表那里，叫的onCreate（）。

Beside onCreate() and onUpgrade() you can override onOpen(). Drop all tables there and call onCreate().

public class MyApplication extends Application {
    protected static final String           LOG_TAG = "MyApplication";

    private static DatabaseAdapter          mDb;

    private static MyApplication    mInstance;

    /**
     * @return The instance of the database adapter.
     */
    public static DatabaseAdapter getDatabaseAdapter() {
        return mDb;
    }

    /**
     * @return The instance of the application.
     */
    public static Context getInstance() {
        return mInstance;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        Log.w(LOG_TAG, "Application::onCreate");
        mInstance = this;
        mDb = new DatabaseAdapter();
    }

    @Override
    public void onTerminate() {
        // Close the internal db
        getDatabaseAdapter().close(DatabaseAdapter.INTERNAL);

        Log.e(LOG_TAG, "::onTerminate::");
        super.onTerminate();
    }
}

子类应用程序的好处是，这将总是叫当您的应用程序启动或终止。独立启动的活动。 像开放的全球业务/关闭数据库应该放在这里。

The advantage of subclassing Application is that this will be called always when your application is started or terminated. Independent of the activity that is started. Global operations like open/close a database should be placed here.

文件：

基类为那些谁需要   保持全球应用程序状态。您   可以通过提供自己的实现   在指定其名字您   AndroidManifest.xml中的   标记，这将导致该类别是   实例为您当过程   为您的应用程序/包   创建。

Base class for those who need to maintain global application state. You can provide your own implementation by specifying its name in your AndroidManifest.xml's tag, which will cause that class to be instantiated for you when the process for your application/package is created.

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