Sqlite数据库应该只创建一次。

Question

我开发了一个具有C2DM功能的项目。每当服务器上有数据可用时，服务器就会将数据推送到所有拥有此应用程序的设备(在我的情况下是一个小消息)。

现在我的问题是，每次消息到达时是否都会创建数据库和表格？以下是我的代码：

 public class MessageHelper extends Activity
    {
        public String str; 
        public int sts;
        public Date timeStamp;

        protected void onCreate(Bundle savedInstanceState) 
        {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);

            Bundle extras = getIntent().getExtras();
            if (extras != null) {
                this.str = extras.getString("msgg");
                Log.d("C2DM", this.str);
            }

            // Create a ref of SQLite
            SQLiteDatabase db;

            //use tat ref to open or create a table 
            db = openOrCreateDatabase( "/data/data/de.vogella.android.c2dm.simpleclient/app_database/file__0/0000000000000001.db", SQLiteDatabase.CREATE_IF_NECESSARY, null);

            try 
            {
                //initialsiging a query with all the table fields 
                final String CREATE_TABLE_CONTAIN = "CREATE TABLE IF NOT EXISTS tbl_Message4("
                        + "id INTEGER PRIMARY KEY AUTOINCREMENT,"
                        + "msg TEXT not null," 
                        + "msg_time INTEGER not null,"
                        + "msg_status INTEGER not null);";

                //execute the above query
                db.execSQL(CREATE_TABLE_CONTAIN);

                timeStamp = new Date();

                String sql =
                        "INSERT or replace INTO tbl_Message4 (msg,msg_time,msg_status) VALUES('"+this.str+"' ,'"+this.timeStamp+"' , 0)" ;       
                db.execSQL(sql);
        }
    }

我有一个名为MessageReceiver的类，它扩展了BroadcastReceiver。每当收到一条消息时，该类会被执行，从而加载MessageHelper.class。以下是MessageReceiver的代码：

public class C2DMMessageReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        Log.w("C2DM", "Message Receiver called");
        if ("com.google.android.c2dm.intent.RECEIVE".equals(action)) {
            Log.w("C2DM", "Received message");
            final String payload = intent.getStringExtra("payload");
            Log.d("C2DM", "dmControl: payload = " + payload);
            // TODO Send this to my application server to get the real data
            // Lets make something visible to show that we received the message
            createNotification(context, payload);

        }
    }

    public void createNotification(Context context, String payload) {
        NotificationManager notificationManager = (NotificationManager) context
                .getSystemService(Context.NOTIFICATION_SERVICE);
        Notification notification = new Notification(R.drawable.ic_launcher,
                "Message received", System.currentTimeMillis());
        // Hide the notification after its selected
        notification.flags |= Notification.FLAG_AUTO_CANCEL;

        //Intent intent = new Intent(context, MessageReceivedActivity.class);
        //intent.putExtra("payload", payload);

        Intent intent = new Intent(context, MessageHelper.class);
        intent.putExtra("msgg", payload);
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        context.startActivity(intent);
        //PendingIntent pendingIntent = PendingIntent.getActivity(context, 0, intent, 0);
        //notification.setLatestEventInfo(context, "Message", "New message received", pendingIntent);
        //notificationManager.notify(0, notification);

    }

}

当应用程序首次安装时，应创建一个数据库。

提前致谢，

TheIlleterate

- TheIlliterate

---

请参考 http://www.vogella.com/articles/AndroidSQLite/article.html#databasetutorial 中的 SQLiteOpenHelper - 它只会在需要时创建数据库。 - zapl

Answer 1

只有在名称没有改变时，数据库才会被创建一次。是的，在你的应用程序首次启动活动 MessageHelper 时它才会被创建。

- waqaslam

Answer 2

数据库将只创建一次，使用单个名称。

您可以选择使用此代码以使其更加简便。

http://www.vogella.com/articles/AndroidSQLite/article.html

- Dheeresh Singh

Answer 3

"

如果不存在，则“CREATE TABLE IF NOT EXISTS”将创建表格。因此，它只会创建一次。 您是否在其他地方删除了此表格？

"

- Mufazzal