I'm working on an iPhone application that should work in offline and online modes.
In it's online mode it's supposed to feed all the information the user enters to a webservice backed by GWT/GAE.
In it's offline mode it's supposed to store the information locally, and when connection is available sync it up to the web service.
Currently my plan is as follows:
Provide a connection between an app and a webservice using Protobuffers for efficient over-the-wire communication
Work with local DB using Core Data
Poll the network status, and when available sync the database and keep some sort of local-db-to-remote-db key synchronization.
The question is - am I in the right direction? Are the standard patterns for implementing this? Maybe someone can point me to an open-source application that works in a similar fashion?
I am really new to iPhone coding, and would be very glad to hear any suggestions.
Thanks
I think you've blurring the questions together.
If you've got a question about making a GWT web interface, that's one question.
Questions about how to sync an iPhone to a web service are a different question. For that, you don't want to use GWT's RPCs for syncing, as you'd have to fake out the 'browser-side' of the serialization system in your iPhone code, which GWT normally provides for you.
about system design direction:
First if there is no REAL need do not create 2 different apps one GWT and other iPhone
create one but well written GWT app. It will work off line no problem and will manage your data using HTML feature -- offline application cache
If it a must to create 2 separate apps
than at least save yourself effort and do not write server twice as if you go with standard GWT aproach you will almost sertanly fail to talk to server from stand alone app (it is zipped JSON over HTTP with some tricky headers...) or will write things twise so look in to the RestLet library it well supported by the GAE.
About the way to keep sync with offline / online switching:
There are several aproaches to consider and all of them are not perfect. So when you conseder yours think of what youser expects... Do not be Microsoft Word do not try to outsmart the user.
If there at least one scenario in the use cases that demand user intervention to merge changes (And there will be - take it to the bank) - than you will have implement UI for this - than there is a good reason to use it often - user will get used to it. it better than it will see it in a while since he started to use the app because a need fro it is rare because you implemented a super duper merging logic that asks user only in very special cases... Don't do it.
balance the effort. Because the mess that a bug in such code will introduce to user is much more painful than the benefit all together.
so the HOW:
The one way is the Do-UnDo way.
While off line - keep the log of actions user did on data in timed order user did them
as soon as you connected - send to server and execute them. Same from server to client.
Will work fine in most cases as long as you are not writing a Photoshop kind of software with huge amounts of data per operation. Also referred as Action Pattern by the GangOfFour.
Another way is a source control way. - Versions and may be even locks. very application dependent. DBMS internally some times use it for transactions implementations.
And there is always an option to be Read Only when Ofline :-)
Wonder if you have considered using a Sync Framework to manage the synchronization. If that interests you can take a look at the open source project, OpenMobster's Sync service. You can do the following sync operations
two-way
one-way client
one-way device
bootup
Besides that, all modifications are automatically tracked and synced with the Cloud. You can have your app offline when network connection is down. It will track any changes and automatically in the background synchronize it with the cloud when the connection returns. It also provides synchronization like iCloud across multiple devices
Also, modifications in the Cloud are synched using Push notifications, so the data is always current even if it is stored locally.
Here is a link to the open source project: http://openmobster.googlecode.com
Here is a link to iPhone App Sync: http://code.google.com/p/openmobster/wiki/iPhoneSyncApp
Related
I have 2 closed-source application that must share the same data at some point. Both uses REST APIs.
An actual example are helpdesk tickets, they can be created on both applications and i need to update the data on one application when the user adds a new ticket/closes a ticket on the other application and vice versa.
Since is closed-source I can't really modify che code.
I was thinking I can create a third application that every 5 minutes or so, list both applications' tickets for differences on the precedent call, and if the data is different from the precedent call it updates the other application too.
Is there a better way of doing this?
With closed-source applications it's nearly impossible to get something out of them, unless they have some plugin-based setup that you can hook into.
The most efficient way in terms of costs would be to have the first application publish a message on a queue, or call a web-hook that you set, whenever the event is triggered. But as I mentioned, the application needs to support that.
So yeah, your solution is pretty much everything you can do for now, but keep in mind the challenges that you may encounter over time:
What if the results of both APIs are too large to be compared directly? Maybe you need to think about paging the results.
What if your app crashes and you loose the previous state? You need to somehow back it up in an external source
How often you should poll the API to make sure you're getting the updates you need, while keeping a good performance for the existing traffic?
our devices (microscopes with cameras) produce images and additional information to each image.
Now a middleware supplies wants to connect these devices to lab automation system. They have to acquire the data and we have to provide it. An astonishing thing for me was their interface suggestion - a very cryptical token separated format (ASTM E1394-97). Unfortunatelly, they even can't accomodate images in their protocol, and are aiming to get file-paths.
I thought it is not the up-to date approach. While lookink for alternatives, I saw CoachDB.
So, my idea was, our devices would import data including images in CoachDB and they could get the data. It seems even, that using mustache, we could produce the format they want (ascii-text) and placing URLs as image references instead of path's.
My question is, did someone applied CoachDB for such a use case already? It seems to be a little-bit misuse of CoachDB, as the main intention is interface not data storage. Another point disturbing me is, that the inventor of CoachDB went to other project Coachbase. Could it mean lack of support for CoachDB in the future?
Thank you very much for any insights and suggestions!
It's ok use-case and actually we're using CouchDB in such way - as proxing middleware between medical laboratory analyzers and LIS. Some of them publish images or pdf data on shared folders and we'd just loading them into related document as attachments.
More over you'd like to know, CouchDB is able to serve external processes (aka os_daemons) and take care about their lifespan: restarting if someone had terminated and starting right after you update config options through HTTP interface. This helps to setup ASTM client and server processes since this protocol is different from HTTP (which is native for CouchDB) which communicates with devices and creates documents as regular CouchDB clients. In same way you may setup daemons to monitor shared folders for specific files. And all this is just CouchDB with few "low bounded" plugins.
I am sorry for asking such a noob question. I know that one way of storing data on the iphone via database is using SQLite, but after reading for a while it seems that the database is local and therefore each application has a copy of the database? is this right? if that is the case then what if I have two ipod with the same apps. and ipod A wants to update the database, then the data isn't reflected on ipod B?? Sorry for the noob questions
You overcome this by having a server which can synchronise the data between the apps. This is actually a much bigger problem than you might first think. In sonatribe.com we're having to consider situations where users aren't connected to the internet - so we queue the users actions and then push the data to the server when the device is connected. You then have to consider which database is the priority? Which one over writes the other when there are conflicts.
We also release new data for new events regularly - this data is then synchronised when the app is fired up.
One of the lessons we learned was that it's better to keep the number of calls down - connecting is expensive - but once connected the flow of data is fast.
FWIW - we went with MonoTouch - and the main reason was for the integration with WCF and the data capabilities (LINQ) of .NET. Using the SIlverlight profile and svcutil it's easy to get connected and communicate with web services passing complex objects over the wire - very handy for this sort of thing.
You also need to consider users who are on a limited data contract. We have the ability to turn off auto synch with the server in the settings. This is also useful for when our users are actually at the music festivals - in the UK, reception is renowned for being bad at events like this due to the sheer volume of people in one space. Although this is improving, users will appreciate the fact that they can stop the app communicating with a server on their behalf.
I've got a database on my server which is about 3mb big. I'd like to ship that with my iphone application.
The most important thing is that I'd like to promote changes to the database (insert, updates, deletes) to the iphone. What's the best way of doing that? I mean - what is necessary on
- the server
- the client (= iphone)
- between; how to transfer this data?
I'm pretty free in using technologies serverside; right now, I've got an sqlite-database on the server filled with the data I'd like to sync to the iphones.
How often do you need the database to be updated, and how urgent are the changes?
If the database updates are infrequent and non-urgent, I'd have the app check for a new version of the database on startup, and if it has changed, download the entire new file.
The app would always download a small metadata file from a known URL on startup. The metadata file contains an version identifier for the latest version and a location where that version of the database can be downloaded. If the version identifier has changed from the version the app already has, will download the new version. If the version identifier has not changed, or if it can't check, the app can keep using the version it has.
Pro tip: if you want to show a progress bar for the download, include the size of the database in the metadata file. Cell networks often have transparent proxies that strip out the Content-Length header from HTTP responses.
Try using web hooks.
The concept of a WebHook is simple. A
WebHook is an HTTP callback: an HTTP
POST that occurs when something
happens; a simple event-notification
via HTTP POST.
A web application implementing
WebHooks will POST a message to a URL
when certain things happen. When a web
application enables users to register
their own URLs, the users can then
extend, customize, and integrate that
application with their own custom
extensions or even with other
applications around the web. For the
user, WebHooks are a way to receive
valuable information when it happens,
rather than continually polling for
that data and receiving nothing
valuable most of the time. WebHooks
have enormous potential and are
limited only by your imagination! (No,
it can't wash the dishes. Yet.)
You can find out more on Webhooks here:
http://www.webhooks.org/ and http://webhooks.pbworks.com/
Wonder if you have considered using a Sync Framework to manage the synchronization. If that interests you can take a look at the open source project, OpenMobster's Sync service. You can do the following sync operations
two-way
one-way client
one-way device
bootup
Besides that, all modifications are automatically tracked and synced with the Cloud. You can have your app offline when network connection is down. It will track any changes and automatically in the background synchronize it with the cloud when the connection returns. It also provides synchronization like iCloud across multiple devices
Also, modifications in the Cloud are synched using Push notifications, so the data is always current even if it is stored locally.
Here is a link to the open source project: http://openmobster.googlecode.com
Here is a link to iPhone App Sync: http://code.google.com/p/openmobster/wiki/iPhoneSyncApp
I'm looking into building an application which works just as well offline as it does online. Since the application cannot communicate with the server while in offline, there is some level of synchronization which needs to take place.
What are some good tools to read about and start thinking about when planning offline operations with synchronization for your iPhone?
What tools would I have to create on my own, versus tools that apple already provides to help with this particular issue?
I've been working on an app that handles this exact behavior for the last 2 months or so. It has a small subset of functions which are online only and a large set of functionality that is offline/online.
I'm using sqlite for local storage as suggested here with a modified version of the sqlitepersistentobjects library. The base version of sqlitepersistentobjects is not thread safe so watch out if you are using it. (check out objectiverecord in: objectivesync for a thread safe alternative but be prepared to dig into the code). If you are willing to develop for the 3.0 sdk then core data is another possibility for a sqlite library.
The overall architecture is simple enough I have modeled local storage using sqlite and remote interaction using objective resource against a rails app and REST api. It can use either xml or json for data serialization.
When an object is modified locally the change is first saved to the sqlite database record for that object and then added to a queue which is serialized and stored in the local sqlite db as well. (The queue can then be processed at any time)
If there is a connection available any queued local changes are deserialized and added to an NSOperationQueue which then processes them in the background.
In order to make this all work I've subclassed NSOperation so that it can support several types of remote queue operations - create, update, delete essentially using objective resource to make the remote requests.
The nice thing about using NSOperationQueue and NSOperation is that they handle the background threading for you so I'd highly recommend having a look at the apple docs for those classes and also at the apple threading guide.
When the application loads there is a bit of remote checking done and processed in the background to pull down the latest data - although to be honest I am still changing the way this behaves a bit.
That's a quick overview of what I've had to deal with so far...hope it helps a little.
there are plenty of application on the app store which rely on both online as well as offline data
what you should really be doing is on start of your app, run a background thread (which runs silently so your user never sees any delay). this thread downloads the latest data from your server and pushes it into your local database (sqlite is the best choice)
make sure you implement some kind of data versioning so that your app only downloads data which is actually changed since last download - else you would unnecessarily be downloading the entire dataset which can be quite huge (depending upon your app requirements)
also make sure to test for internet connectivity when doing this. if no internet is available, alert the user for sure
this way you get the best of both worlds. users when away from internet can still use your app with their local sqlite data
in iphone os 3.0 apple has introduced push services - where you can simply "PUSH" your data instead of doing a "PULL" however this is not available in the current iPhone OS (2.x.x)
Push is probably not a viable option here, since the amount of data you can push is miniscule, and basically comes back to "tell my app to make a server call". We use an online/offline model in Satchel. Whenever we have to communicate with the server, we bundle that communication (a URL and possibly some POST data) and store it to a database. If we're online, we pull it right back out, send it, and when we get a valid response back, we remove the record from the database. If we're offline, those rows build up, and the next time we ARE online, they get sent out. This is not a workable model in all situations, but can be adapted to most.
In 3.0, you've got access to CoreData, which is a great data management tool. Other than that, the NSURLXXX family is your friend.
I would store all the information I gather while offline in a SQLite database. Then, on user 's request, you can SYNC all the stored information with a server using HTTP or a custom TCP/IP protocol you can come up with.
I have been using this approach on Palm OS applications for almost 10 years now, and they do work very effectively.
As far as I know, the only "tool" you will have to accomplish this is plain old OBJECTIVE-C with Cocoa Touch. Although you could use some TCP/IP C++ libraries that will make your life easier if you decide to implement your own protocol.
Wonder if you have considered using a Sync Framework to manage the synchronization. If that interests you can take a look at the open source project, OpenMobster's Sync service. You can do the following sync operations
two-way
one-way client
one-way device
bootup
Besides that, all modifications are automatically tracked and synced with the Cloud. You can have your app offline when network connection is down. It will track any changes and automatically in the background synchronize it with the cloud when the connection returns. It also provides synchronization like iCloud across multiple devices
Also, modifications in the Cloud are synched using Push notifications, so the data is always current even if it is stored locally.
Here is a link to the open source project: http://openmobster.googlecode.com
Here is a link to iPhone App Sync: http://code.google.com/p/openmobster/wiki/iPhoneSyncApp