In my iPhone/iPad app I'm handling all network and web-API-requests through a "APIManager" (singleton, created in AppDelegate).
Currently the APIManager contains only one single ASINetworkQueue, to which APIRequests (subclass of ASIHTTPRequest) are added and executed. In the userInfo of each APIRequest some additional information to handle the request is added (like whether the response should be parsed into Core Data - and if so, which entity - or not).
When the user moves from one view (ViewA) to another (ViewX), I would like to have the possibility to cancel all the requests that ViewA have asked the APIManager to perform, while letting others continue.
Is there some functionality to find a certain request in a ASINetworkQueue (or NSOperationQueue) and send a cancellation message to it? Maybe using parameters added to the userInfo of the request?
Thanks in advance!
[queue operations] will return an NSArray of items in the queue, which you can then iterate and call 'cancel' on any you like.
Something like:
for (ASIHTTPRequest *req in [queue operations])
{
if (shouldCancel(req))
[req cancel];
}
Related
I have ASINetworkQueue with more than 1500 requests in it. Performing this number of requests takes for a while. If user leaves view controller while this queue is running the OS deallocates the view controller and I get "message sent to deallocated instance" error.
I have tried to use
[self.queue cancelAllOperations];
in dealloc method, but seems like it cancels only requests that are waiting in queue, not the request that is currently running and I'm getting the same error.
What is the correct way to handle this situation? Is it possible to make the view controller not to be deallocated while queue is not finished even if user left it? Or is there a way to cancel all requests (including requests that are running) in queue?
The suggestions by #darvids0n and #AlexReynolds are both good.
The problem is probably that the delegate for the current request is still set, so it tries to notify the (now deallocated) delegated that it's been canceled.
You can most likely avoid this by setting all the delegates to nil instead:
for (ASIHTTPRequest *req in queue.operations)
{
[req setDelegate:nil];
[req cancel];
}
[queue setDelegate:nil];
Detach the network queue's lifespan from that of the view controller. For example, have it managed by the application delegate, which should be alive as long as the application is alive.
When the view controller is dismissed, cancel all operations in the app delegate's network queue. Even if the view controller is dead, the app delegate should keep chugging along, giving enough time for the network queue to do its cleanup work.
If you think you'll have multiple queues, keep references to them in an array or dictionary with some identifier or index so that you can keep track of them separate from their respective view controllers.
I have an application in which I am required to connect to the internet after a view is loaded. However, if I put this code in the viewDidLoad method the parent view freezes, and then unfreezes after the connection onto the new view. However, I would like the new view to load FIRST, and then to start the connection. I tried using viewDidAppear:, however I am getting the same issue.
Also, will any animations continue playing during the connection? Will the UI be responsive? If not, is multithreading the way to go?
Here is some of my code:
-(void)viewDidLoad {
[super viewDidLoad];
//Do some other view initialization
//Connect is a class I use to connect to the internet
[Connect getData:someString];
}
When I put the code in viewDidAppear the same thing happens.
Connection code:
NSMutableURLRequest *request = [[NSURLRequest alloc] initWithURL:url];
NSHTTPURLResponse *response;
NSError *error;
NSData *responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
Also, I forgot to mention that I am running a regular expression as well after the connection.
As the name of the method says, the view has already been loaded when viewDidLoad executes.
Generally, be sure to use asynchronous connections to connect to the internet. Never block the main thread.
it is easier than you may think.
All you need is some thread management. On the view did Do:
[NSThread detachNewThreadSelector:#selector(yourMethod:) toTarget:yourTarget withObject:yourObject];
and later in another part do:
- (void)yourMethod:(id)sender{
//download the info but do not update the GUI
[self performSelectorOnMainThread:#selector(updatingTheGUI:) withObject:yourObject waitUntilDone:NO]
}
- (void)updatingTheGUI:(id)sender{
//Update your GUI
}
You will notice that the viewDidLoad method documentation of UIViewController states:
...Called after the controller’s view is loaded into memory.
This doesn't necessarily mean that it's called after the view is displayed on screen.
To answer your other questions, if you make your network request the way you have described, no, animations will not continue playing while the request is in progress and no, you can't guarantee that the UI will be responsive. This is because the network request will take an unknown amount of time. Therefore, if you make the request on the main thread, the main thread will be blocked for that period of time, however long it takes.
And, as for the last question, is multithreading the way to go? As others have stated, the easiest and probably most popular way of handling this is to initialize the NSURLConnection with initWithRequest:delegate:. The delegate being your UIViewController or Connect class, or whatever class you want to conform to the NSURLConnectionDelegate protocol and use the NSURLConnectionDelegate methods to process the downloaded data. NSURLConnection will do the work asynchronously and keep the main thread free to handle animations, displaying the UI, etc.
I know it sounds a bad idea for your app. performance but try giving a delay or sleep in between to check if it works that way. Later try to implement the asynchronous call as someone earlier stated..
I'm running an http request with my view controller as the delegate using ASIHTTP, if the user leaves the view controller before the request is done, I get a EXC_BAD_ACCESS in the ASIHTTP code that is doing an if ( delegate ... )
Is there something I have to do in my view controller dealloc? I want to simply drop the request if the user leaves.
The most common reason for problems like this is an ASIHTTPRequest object that is still active and where its delegate field points at an object that is now destroyed. The EXC_BAD_ACCESS will then happen when ASIHTTPRequest tries to tell the delegate the request has finished and so on.
Your dealloc method for the object that is the asihttprequest delegate should have:
request.delegate = nil;
[request cancel]
[request release]
If you have only one request active at a time, you must have this same code anywhere you start a new request, to ensure that any previous request is correctly cancelled.
If you have more than one request active, you will need to keep track of all of them, and cancel and nil the delegate of all of them.
For reference, I've been using ASIHTTPRequest for ~18 months, and have contributed back a number of fixes for difficult race conditions related to cancelling requests.
I have a view that includes a UIWebView as well as an iAD AdBannerView.
To optimize the experience and reduce bandwidth contention - I suspend the UIWebView's network activity when the iAd "detail view" is being loaded and resume it when the user returns from the ad. Currently, I simply do the following:
-(BOOL)bannerViewActionShouldBegin:(ADBannerView *)banner willLeaveApplication:(BOOL)willLeave
{
if (self.webView.loading) {
[self.webView stopLoading];
self.loadingWasInterrupted = TRUE;
}
return YES;
}
-(void)bannerViewActionDidFinish:(ADBannerView *)banner
{
if (self.loadingWasInterrupted) {
//Should use loadRequest: instead?
[self.webView reload];
}
}
I'm trying to understand if it there is any difference between calling reload vs. loadRequest: a second time, and if so, which is more efficient.
I'm guessing reload simply just saves you having to hold onto the request object and really does the same thing but I'd like to know for sure. The docs and header don't offer any clue.
I understand I could pick apart the network activity to understand what's happening but would appreciate any insight from someone who has looked at this before or who generally understands if reload behavior differs from loadRequest at all. Thank you.
Okay, a fairly complicated solution but never the less one that I think might work for you:
Define a custom protocol handler for http:
http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/URLLoadingSystem/URLLoadingSystem.html#//apple_ref/doc/uid/10000165i
Using NSURLProtocol as the subclass. The handler will start a NSURLConnection, and return the data as it comes in to the client (in this case this will be the UIWebView that initiated the connection). Have it add itself as an observer to NSNotificationCenter for a "Pause" notification.
When you would like to display an iAd, you can send your pause notification, this will cancel the NSURLConnection (but not the NSURLProtocol, which will remain open and loading, and thus your webview will continue to appear as if it were loading).
Then when the add is finished you can send a "resume" notification (much the same), except in this case any active NSURLProtocol handlers receiving the notification will create new NSURLConnections, using the Range: header to resume where they left off:
iphone sdk: pausing NSURLConnection?
Some caveats:
Only will work when browsing websites that support the resume header (otherwise you might have to start the connection anew, and just ignore data prior to the latest byte received).
Your NSURLRequests should be formed so that they don't have a timeout. (if you want a timeout then it should be in the NSURLProtocol handlers NSURLConnections).
I'm guessing here, but I believe the reload is doing a loadRequest: internally. If you are really intent on testing this you cold add a temporary subclass to UIWebView and override the reload and loadRequest methods just for the sake of logging.
- (void)reload
{
NSLog(#"reload called");
[super reload];
}
- (void)loadRequest:(NSURLRequest *)request
{
NSLog(#"loadRequest called");
[super loadRequest:request];
}
When you call the method "loadRequest", you call it like
[webview loadRquest:[NSURLRequest requestWithURL:[NSURL URLWithString:#"http://www.ururl.com"]]];
But when u call "reload", u just instruct to reload whatever the current request is.
So basically in latter case , u are saving urself from creating a url from string and then a request from url and that makes it pretty convenient for use.
As per case of functionality, reload itself calls loadRequest so basically there is no difference in terms of efficiency and even in speed.
However basically for ur case and in many of my cases , the thing which we want but Apple has not given us is something like:-
[webview pauseLoading];
[webview resumeLoading];
So to sum up the whole thing , use any of them but if u r lazy like me to again specify the urlrequest just use "reload"
Apologies
Sorry guys I used to think that reload must be calling loadRequest but when I tried NWCoder's method, it doesnot call loadRequest on calling reload. But I still think reload and loadRquest follows the same method for loading the page
I have an UITabBar based iPhone app with 4 different UIWebViews under every tab. Right now all the UIWebViews load on startup and it takes a little bit too long.
I would like to load the default tab's UIWebView first, then load the others in the background. What is the best way to do this?
I have seperate ViewControllers set up for each tab and have this in every .m file:
- (void)viewDidLoad {
NSString *urlAddress2 = #"http://google.com ";
//Create a URL object.
NSURL *url2 = [NSURL URLWithString:urlAddress2];
//URL Requst Object
NSURLRequest *requestObj2 = [NSURLRequest requestWithURL:url2];
//Load the request in the UIWebView.
[webView2 loadRequest:requestObj2];
}
Is there a simple way to tell the other 3 tabs to start loading a few seconds after launch instead of at launch? Would that be a good idea?
Thanks a lot!
I've gotten around this issue by implementing a model layer through which all requests pass. Requests are queued and serviced in priority order, generally one at a time. I've added specific methods to allow a controller to escalate the priority of requests so that, if necessary, two or more requests will be active at once. When a request finishes, it alerts it delegate (the WebView's controller) that data is ready to be loaded.
Depending on how you want to set things up, you can put a callback in "webViewDidFinishLoad" (or, perhaps, shouldStartLoadWithRequest or webViewDidStartLoad) that triggers the model layer to dequeue and service the next request. For safety, you'll also want a timeout in the model layer.
Note: you'll also need to add some custom code into shouldStartLoadWithRequest to differentiate between clicks and the model layer pushing data in. I.e. you'll want to return NO or YES depending on the navigationType.
If you use ASIHTTPRequest instead of NSURLRequest, you can fire a synchronous request for the first URL. Once that request is complete, you can then fire off the other three URL requests asynchronously (i.e., in the background).
You can use NSTimer, or do the loading in viewDidAppear or similar.
Use viewDidAppear. This will be sent to the controller after the view fully appears and animations end.