I'm making an iOS app. This app will also have a integrated chat in it, our chat server works with long polling. The app has multiple views, ex :
Login View -> Main Menu View -> etc. etc.
Now my problem is that I want the long polling to continue across all the view controller, so that the app itself is constantly connected to the long polling server, and when the response is received, the response data is processed based on the current view so that appropriate actions can be taken based on the current view.
So, I have a really bad idea in mind to go about this: Start Long polling after every view change.
Please help me out. Reply if you need more info. Thanks!
Take advantage of Singleton class
1. Create Singleton class
2. Start your session of long polling in Appdelegate AppDidbecomeActive function
then you can use it in every class and can reset it as well without extra headache.
3. and close your long polling in Appdelegate AppDidEnterintoBackground if you want to close it as per your requirements.
4. close it in appwillterminate.
Hope that will help you.
Related
Me and my team are currently rookie developers in Objective-C (less than 3 months in) working on the development of a simple tab based app with network capabilities that contains a navigator controller with a table view and a corresponding detailed view in each tab. The target is iOS 4 sdk.
On the networking side, we have a single class that functions as a Singleton that processes the NSURLConnection for each one of the views in order to retrieve the data we need for each of the table views.
The functionality works fine and we can retrieve the data correctly but only if the user doesn't change views until the petition is over or the button of the same petition (example: Login button) is pressed on again. Otherwise, different mistakes can happen. For example, an error message that should only be displayed on the root view of one of the navigation controllers appears on the detailed view and vice versa.
We suspect that the issue is that we are currently handling only a single delegate on the Singleton for the "active view" and that we should change it to support a behavior based on the native Mail app in which you can change views while the data that was asked for in each one of the views keeps loading and updating correctly separately.
We have looked over stackoverflow and other websites and we haven't found a proper methodology to follow. We were considering using an NSOperationQueue and wrapping the NSURLConnections on an NSOperation, but we are not sure if that's the proper approach.
Does anyone have any suggestions on the proper way to handle multiple asynchronous NSURLConnections to update multiple views, both parent and child, almost simultaneously at the whim of the user's interaction? Ideally, we don't want to block the UI or disable the buttons as we have been recommended.
Thank you for your time!
Edit - forgot to add, one of the project restrictions set by our client is that we can only use the native iOS sdk network framework and not the ASIHTTPRequest framework or similar. At the same time, we also forgot to add that we are not uploading any information, we are only retrieving it from the WS.
One suggestion is to use NSOperations and a NSOperationsQueue. The nice thing about this arrangement is you can quickly cancel any in-process or queued work (if say the user hits the back button.
There is a project on github, NSOperation-WebFetches-MadeEasy that makes this about as painless as it can be. You incorporate one class in your classes - OperationsRunner - which comes with a "how-to-use-me" in OperationsRunner.h, and two skeleton NSOperations classes, one the subclass of another, with the subclass showing how to fetch an image.
I'm sure others will post of other solutions - its almost a problem getting started as there are a huge number of libraries and projects doing this. That said, OperationsRunner is a bit over 100 lines of code, and the operations about the same, so this is really easy to read, understand, use, and modify.
You say that your singleton has a delegate. Delegation is inappropriate when multiple objects are interested in the result. If you wish to continue using a singleton for fetching data, you must switch your pattern to be based on notifications. Your singleton will have responsibility for determining which connection corresponds to which task, and choosing an appropriate notification to be posted.
If you still need help with this, let me know, I'll try to post some sample code.
So I'm working on this application that requests and retrieves webservice content for iPhone. The problem I am running into is this: When I initially request data, it is spawned off as an independent thread so that the application does not become unresponsive due to the network being slow. What this means is that if the user navigates away from the current page before this data finishes downloading, unexpected things can happen.
I have managed to narrow down the problem cases to one relatively simple one: I have some nested tables, so if a user goes down into the "Messages" table, which can sometimes take a little while to download, then back out immediately, and select a different set of messages to view, the previous set of messages ends up loading, because it was still in the queue.
Here are things I have tried:
1) I tried cancelling the operations, but this is futile, because since I only allow one operation in the queue at the time, it triggers immediately
2) I tried validating that the recipient of the data is the same, but this doesn't work because the actual table object is the between the two selections, it just needs a different data set.
Anyone have any general programming suggestions on how to solve this tricky threading problem?
On an iPhone specific note: if I could just stop the user from being able to back out of the messages table, I wouldn't have this problem, because they would basically be locked into that view until the data has finished loading.
Thanks!
This post has some design advice relating to iOS networking and threading. The basic gist of it is "Don't use explicit threading", and I couldn't agree more. NSURLConnection has great built-in functionality for asynchronously loading data from a URL while managing all of the threading for you. They can also be cancelled easily at will.
If you were to use the NSURLConnection paradigm, you can simply cancel any pending request when you back out of the requesting view controller.
I am new to objective-c/cocoa programming. I am making an application which is to constantly sync with a server and keep its view updated.
Now in a nutshell, heres what I thought of: Initiate an NSTimer to trigger every second or two, contact the server, if there is a change, update the view. Is this a good way of doing it?
I have read elsewhere that you can have a thread running in the background which monitors the changes and updates the view. I never worked with threads before and I know they can be quite troublesome and you need a good amount of experience with memory management to get most out of them.
I have one month to get this application done. What do you guys recommend? Just use an NSTimer and do it the way I though of...or learn multithreading and get it done that way (but keep in mind my time frame).
Thanks!
I think using separate thread in this case would be too much. You need to use threads when there is some task that runs for considerable amount of time and can freeze your app for some time.
In your case do this:
Create timer and call some method (say update) every N seconds.
in update send asynchronous request to server and check for any changes.
download data using NSURLConnection delegate and parse. Note: if there is probability that you can receive a huge amount of data from server and its processing can take much time (for example parsing of 2Mb of XML data) then you do need to perform that is a separate thread.
update all listeners (appropriate view controllers for example) with processed data.
continue polling using timer.
Think about requirements. The most relevant questions, IMO, are :
does your application have to get new data while running in background?
does your application need to be responsive, that is, not sluggish when it's fetching new data?
I guess the answer to the first question is probably no. If you are updating a view depending on the data, it's only required to fetch the data when the view is visible. You cannot guarantee always fetching data in background anyway, because iOS can always just kill your application. Anyway, in your application's perspective, multithreading is not relevant to this question. Because either you are updating only in foreground or also in background, your application need no more than one thread.
Multithreading is relevant rather to the second question. If your application has to remain responsive while fetching data, then you will have to run your fetching code on a detached thread. What's more important here is, the update on the user interface (like views) must happen on the main thread again.
Learning multithreading in general is something indeed, but iOS SDK provides a lot of help. Learning how to use operation queue (I guess that's the easiest to learn, but not necessarily the easiest to use) wouldn't take many days. In a month period, you can definitely finish the job.
Again, however, think clearly why you would need multithreading.
Just to give background for my situation, I have a manager singleton that pulls data from a webserver and provides access to the downloaded data. I have several types of views that will consume this data, but only one view at any time will need to receive events.
I was just wondering what people prefer to use when they need to get events from a singleton. Do you use NSNotificationCenter, Target/Action, or delegate?
Thanks for any help.
Are you really, really sure only one view needs to receive events? For instance, you don't have a master view that would need access to the same update that a subview was notified about?
If you truly have only one view controller needing updates at a time ever, I might use a delegate approach. Here's something to consider - what happens if you are in the middle of receiving an update and the user change screens... is that OK? would you cancel the request?
Anything more than one, or if that in-flight changing delegate scenario has issues, then you may well be better off with a notification that anyone can hook into. It's best to keep the notification light with some kind of reference to the change and have the receiver have to look up the altered data.
If there are going to be a large number of events, then you want to stay away from NSNotifications.
For the least amount of overhead I would go with the delegate pattern, although I don't think that target/action has much more overhead than delegates.
Try your favorite way and if there is a problem profile or try a different approach.
I usually start with the easiest to get implemented. For example I once tried to use notifications for some interface code I had written years ago but with 30-60 updates/second the whole interface bogged down unacceptably so I went with delegates which fixed the problem.
I'm pretty new to iPhone development but I'm close to releasing my first app (related to a website I run). The app requires a very large database and as such I've decided to store only the most commonly used data locally, retrieving the other data via a JSON web service call from the database my website runs off.
Whilst performing OK using the simulator (hitting the live DB) searches relying on the web service call have been taking longer than I'd have hoped they would when running on the phone. These calls look much worse when compared to the native searches which are instantaneous. To reduce the relative difference I wanted to put in a fake interstitial (page with activity indicator) for the native searches (the web service searches already use one) but I've been having an issue with the timing of navigation controller pushes when combined with sleep(n).
Anyway, the search section of my app is a navController wihin a tabController tab. When trying to use code like this:
[[tabBarController.viewControllers objectAtIndex:0] pushViewController:(UIViewController *)waitingController animated:YES];
sleep(2);
I find that the push always waits for the sleep to finish before executing when the effect I want is for the viewcontroller to be pushed and then the app to wait for two seconds before continuing to simulate the search process.
I've had some other weird results with navController pushes, on a few occasions I've experienced what seems to be a mashing of two separate viewcontrollers when the one I've pushed as interstitial remains in place content-wise with only the title of the one I want pushed in it's place remaining.
I'm sure that there is a fundamental lack of understanding on my part to blame so I'm hoping for a bit of guidance here.
Cheers,
Alan.
sleep(float) blocks the main thread causing the UI to freeze up. You should instead schedule some action to be performed later using -[NSObject performSelector:withObject:afterDelay:]
Example:
[label performSelector:#selector(setText:) withObject:#"Delayed Hello World!" afterDelay:2.0f];
I would look at changing your architecture and not sleeping on the main thread - not a great user experience!
Look into using NSOperation to control your interactions with the web service - this will allow you to queue up operations and have them run in a specific sequence or in parallel.
NSOperation is a very easy way to provide robust threading operations - and you could choose to make a call back to the main thread with any updates you want to do along the way.
I think this architecture will help you make the user interface much better - but once you have reconfigured your thinking to use operations you will find lots of other benefits.
NB: It took me a few times to really get to grips with NSOperation and NSOperationQueue - but the time I invested was definitely worth it.