I'm using ASIHttpRequest to recieve data from an xml file. However during an asynchronous request as soon as i change the view (back to the previous view using the navigation controller) the application crashes with a EXC_BAD_ACCESS on the main.m
This only happens while the request is being made.
Below is my code:
-(void)ProcessXML{
//Set url from string to url
NSURL *theurl = [NSURL URLWithString:#"http://twitter.com/statuses/user_timeline/2smssupport.xml"];
asirequest = [ASIHTTPRequest requestWithURL:theurl];
[asirequest setDelegate:self];
[asirequest startAsynchronous];
}
- (void)requestFinished:(ASIHTTPRequest *)request
{
NSLog(#"Saving to Defaults");
NSData *responseData = [request responseData];
xmlSaved = responseData;
prefs = [NSUserDefaults standardUserDefaults];
[prefs setObject:responseData forKey:#"xmlDownload"];
rssParser = [[RssParser alloc] loadXMLbyURL:xmlSaved];
[self.tableView reloadData];
NSLog(#"%#",[prefs dataForKey:#"xmlDownload"]);
}
The Process XML method triggers the request and the then received data is processed in the RequestFinished.
There must be something i'm missing with the ASIHTTPRequest but i don't know what it is?
Thanks
This block of code should fix it:
-(void) viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
[request clearDelegatesAndCancel]
}
If the view is being release then the delegate you set on the request is now invalid. Make sure you set the delegate to nil on the view dealloc and also stop the request.
The asirequest object isn't being retained anywhere, so it's being deallocated after ProcessXML returns.
NSZombieEnabled helps you a lot. You can tell which object is causing EXC_BAD_ACCESS.
Are you deallocating the ASIHTTPRequest object when you leave the current view? My guess is that the delegate methods are being called after your view controller has been released.
--
#Simon is right that you do need to set the delegate to nil. What I would do is:
Create an ASIHTTPRequest property in your class and set that property in your ProcessXML method. This simplifies memory management and ensures that the request object will stick around while you need it.
In both your dealloc method and your requestFinished methods, set the request delegate to nil and set self.request = nil;
At the very least, you should set the delegate to nil in your requestFinished method, but you need to remember to stop your request from running if you navigate away from this view controller before it returns, hence setting it to nil in the dealloc method as well.
Related
I am using NSURLConnection to load data from a response. It works as it should, the delegate method connectionDidFinishLoading has the connection instance with the data I need. The problem is that I want to pass some information along with the request so that I can get it when the connection finishes loading:
User wants to share the content of a URL via (Facebook, Twitter,
C, D).
NSURLConnection is used to get the content of the URL
Once I have the content, I use the SL framework
SLComposeViewController:composeViewControllerForServiceType and need
to give it the service type
At this point I don't know what service the user selected in step 1. I'd like to send that with the NSURLConnection.
Can I extend NSURLConnection with a property for this? That seems very heavy-handed. There must be a "right way" to do this.
Many Thanks
Assuming you don't need the delegate-based version of the NSURLConnection process for some other reason, this is a good use case for the block-based version:
- (void)shareContentAtURL:(NSURL *)shareURL viaService:(NSString *)service
{
NSURLRequest *urlRequest = [NSURLRequest requestWithURL:shareURL];
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[NSURLConnection sendAsynchronousRequest:urlRequest queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
{
if ([data length] == 0 && error == nil) {
// handle empty response
} else if (error != nil) {
// handle error
} else {
// back to the main thread for UI stuff
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
// do whatever you do to get something you want to post from the url content
NSString *postText = [self postTextFromData:data];
// present the compose view
SLComposeViewController *vc = [SLComposeViewController composeViewControllerForServiceType:service];
[vc setInitialText:postText];
[self presentViewController:vc animated:YES];
}];
}
}];
}
Since blocks can capture variables from their surrounding scope, you can just use whatever context you already had for the user's choice of service inside the NSURLConnection's completion block.
If you're still wed to the delegate-based NSURLConnection API for whatever reason, you can always use an ivar or some other piece of state attached to whatever object is handling this process: set self.serviceType or some such when the user chooses a service, then refer back to it once you get your content from the NSURLConnectionDelegate methods and are ready to show a compose view.
You could check the URL property of an NSURLConnection instance and determine the service by parsing the baseURL or absoluteString property of the URL with something like - (ServiceType)serviceTypeForURL:(NSURL *)theURL;
All the NSURLConnectionDelegate methods pass the calling NSURLConnection object-so you could get it from
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
or
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
While parsing of the twitter data, I used threads to call the main URL to download the data. It does the downloading perfectly but when I hit the back button while the data is downloading it throws performSelectorOnMainThread message deallocated. I know we can use isCancelled but its not working for me yet. Does anyone have come across this issue and have resolved it.
- (void)LoadTwitterData
{
NSString *urlString =#"http://search.twitter.com/search.json?q=tabc&result_type=recent&rpp=2500";
NSURL *url = [NSURL URLWithString:urlString];
NSString *jsonString = [NSString stringWithContentsOfURL:url];
NSDictionary *values = [jsonString JSONValue];
/**** Throws here *****/
[self performSelectorOnMainThread:#selector(didFinishLoadingResults:) withObject:values waitUntilDone:NO];
}
If you spin off a thread using a selector on self, you need to make sure that self is retained for the duration of that thread, otherwise (as in your case) self can be deallocated and your thread will try to call back into a zombie. The easiest way to do this is to pass self to the thread as an argument. If you use performSelectorInBackground:withObject: you should do something like this:
[self performSelectorInBackground:#selector(LoadTwitterData) withObject:self];
Or if you use NSThread you should pass self to the object: initializer argument.
In fact the safest way to use thread methods is to make the method static like this:
+ (void)LoadTwitterData:(id)arg
{
// ...
MyController *self = arg;
// ... do work
[self performSelectorOnMainThread:#selector(didFinishLoadingResults:)
withObject:values waitUntilDone:NO];
}
This way you are unable to access instance variables by accident which avoids various multi-threading issues. Any and all data the thread needs, including the self to callback to, should be passed in as 'arg', which can be an array or dictionary or whatever you need. This way you know that everything the thread needs will be retained for the duration of the thread, and because you aren't accessing instance variables through self, another thread can't go and change them around underneath you.
Another thing you should do in a thread method is wrap the whole thing with an autorelease pool:
- (void)LoadTwitterData
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
#try {
// ...
} #finally {
[pool drain];
}
}
If LoadTwitterData: is in a background thread, you need to create an Auto release pool (If you haven't already). Surround your code with-
NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
//your code
[pool drain];
A brief over view of what I am trying to do.
I am using the tableView:didSelectRowAtIndexPath: method inside my UITableViewController subclass which is catching a row selection from that view like so...
//..... inside tableView:didSelectRowAtIndexPath:
if (indexPath.section == 0) {
//--- Get the subview ready for use
VehicleSearchResponseTableViewController *vehicleSearchResponseTableViewController = [[VehicleSearchResponseTableViewController alloc] initWithNibName:#"VehicleSearchResponseTableViewController" bundle:nil];
// ...
//--- Sets the back button for the new view that loads
self.navigationItem.backBarButtonItem = [[[UIBarButtonItem alloc] initWithTitle:#"Back" style: UIBarButtonItemStyleBordered target:nil action:nil] autorelease];
// Pass the selected object to the new view controller.
[self.navigationController pushViewController:vehicleSearchResponseTableViewController animated:YES];
if(indexPath.row == 0) {
vehicleSearchResponseTableViewController.title = #"Mans";
EngineRequests *engineRequest = [[EngineRequests alloc] init];
[engineRequest getMans];
[engineRequest release];
}
if(indexPath.row == 1) {
//.... etc etc
As you can see in this method I set up a few things, pushing the new view onto the viewstack and changing the back buttons text, then I go into catching the different rows and then initiating a method in a subclass of nsobject where I want to have all my connection/request stuff going on.
Inside my NSObject I have several different methods for the different cells that you can select on the UITableViewController, basicly they specify different strings that will then initialize my ASIHTTPRequest wrapper to make a connection to the php script and catch all the data that will come back from the database.. NSObject looks like this.
//.... NSObject.m
- (IBAction) getMans
{
NSString *mansString = [[NSString alloc] initWithString:#"mans.php"];
[self grabURLInBackground:mansString];
[manusString release];
}
//....cont....
//--- Connect to server and send request ---------------->>
- (IBAction)grabURLInBackground:(NSString *)setUrlString
{
NSString *startURL = [NSString stringWithFormat:#"http://127.0.0.1:8888/CodeTest/%#", setUrlString];
NSURL *url = [NSURL URLWithString:startURL];
ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];
[request setDelegate:self];
[request startAsynchronous];
}
- (void)requestFinished:(ASIHTTPRequest *)request
{
NSString *responseString = [request responseString]; //Pass request text from server over to NSString
NSData *responseData = [responseString dataUsingEncoding:NSUTF8StringEncoding]; //Create NSData object for Parser Delegate and load with responseString
NSLog(#"stuff %#",responseData);
}
- (void)requestFailed:(ASIHTTPRequest *)request
{
NSError *error = [request error];
NSLog(#"%#", error);
}
From here I would like to pass the data I am getting from the requestFinished method back over to the newly pushed UITableView.. However I have an error before I am able to get this far that I need to solve... if I run the simulator and click back and forth between the views (the main UITableViewController with the cells and then the newly popped view where I want to put the data) the application falls over and pops up an error in main.m Thread 1: program receive signal EXC_BAD_ACCESS.. I just don;t know whats causing because from what I can tell my code is not so bad.
Also when I debug my application I notice that once grabURLInBackground method has finished it bounces out back to the getMans method then goes back over to the UITableViewController and continues through the if statements, completely neglecting the requestFinished and requestFailed methods, and I just cannot figure out why.
I guess I am not sure if I am calling the methods and functions I need to use in the right places so if you have any suggestions or answers on how I can improve or if you know where my error is coming form that would be greatly appreciated.
There's a few issues with the code above but I'd guess that your bad access exception is due to the handling of your EngineRequests and use of AsiHttpRequest.
The code here
EngineRequests *engineRequest = [[EngineRequests alloc] init];
[engineRequest getMans];
[engineRequest release];
effectively creates an object then deallocates as soon as getMans has finished running.
Then inside the engineRequest object this code
[request setDelegate:self];
[request startAsynchronous];
requests that AsiHttpRequest notify the almost certainly released object once the request has completed.
There may be other issues at work here but I'd start by restructuring to try to keep this object around until at least after it's received the response from AsiHttpRequest.
Hard to tell from the brief overview, but generally when you bad_access and end up in the main application method, it's usually because you autoreleased something, then released it, and it craps out when the autorelease pool is drained. Might want to turn on NSZombiesEnabled and look for memory problems.
Who does receive your request?
The sender (and receiver) object is engineRequest.
But you release Engine Request in that very moment after you issued the async request (by mens of the getMans Method.
I would suggest that you
1. move the code
vehicleSearchResponseTableViewController.title = #"Mans";
EngineRequests *engineRequest = [[EngineRequests alloc] init];
[engineRequest getMans];
[engineRequest release];
from your UITableViewController's didSelectRowAtIndexPath method to your vehicleSearchResponseTableViewController's viewDidLoad method.
2. to retain your EngineRequests object and keep it in some instance variable within vehicleSearchResponseTableViewControllerand do not release it before the request is completely processed, either successfully or in error.
Kinda stuck on this problem and I'm not sure, where I've gone wrong. Heres what I'm doing:
Class calls:
- (void)updateApplicationDataInBackground {
updateView = [[UpdatingView alloc] init];
[self.view addSubview:updateView.view];
DataSynchronizer *dataSynchronizer = [[DataSynchronizer alloc] init];
[NSThread detachNewThreadSelector:#selector(initWithDataRequest:) toTarget:dataSynchronizer withObject:self];
[dataSynchronizer release];
This creates a thread to retrieve data from the server and parse it. In DataSynchronizer this is the method being called:
- (void)initWithDataRequest:(id)parent {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
controller = parent;
NSLog(#"DataSynchronizer initWithDataRequest called");
NSURL *url = [NSURL URLWithString: ApiUrl];
ASIFormDataRequest *request = [ASIFormDataRequest requestWithURL:url];
[request setPostValue:ApiKey forKey:#"key"];
[request setPostValue:ApiPass forKey:#"password"];
[request setPostValue:#"somevalue" forKey:#"framework"];
[request setPostValue:#"somevalue" forKey:#"method"];
[request setDidFinishSelector:#selector(parseResult:)];
[request setDidFailSelector:#selector(requestError:)];
[request setTimeOutSeconds:60];
[request setDelegate:self];
[request startAsynchronous];
[pool release];
After my data is received I parse the contents and do my data synch. This is all working as expected. I've decided to throw in a UIProgressView so the user can see what is going on with this request, this progress view lives in updateView which is created in the updateApplicationDataInBackground.
I'm not trying to show progress for the web service call but simply when milestones are reached in the data processing. In the DidFinishSelector its calling parseResult
There are five method its calls with the response data:
[self parseData:[data objectForKey:#"types"] forObject:[Types class] andParent:nil];
[controller performSelectorOnMainThread:#selector(updateProgress:) withObject:[NSNumber numberWithFloat:.4] waitUntilDone:YES];
After each process I'm trying to update the UIProgressView, it will never update. Now if I simply call performSelectorOnMainThread from outside the ASIHTTPRequest it works as expected, but not within the DidFinishSelector. I've tried many variations on this where it calls a local method which updates the mainThread, where I simply use performSelector. Nothing works, how do I update the the UIProgessView?
Is the problem a thread spawning a thread?
Thanks
EDIT:
Looks like the DidFinishSelector is being called on the main thread already. I've updated my code to simply call:
[controller updateProgress:[NSNumber numberWithFloat:.8]]
Still no luck....
Realized it might be helpful to see the UIProgessView update method.
- (void)updateProgress:(NSNumber *)progress {
float newProgess = [progress floatValue];
[updateView.myProgress setProgress: newProgess];
Ok so it looks like I found my own answer after changing somethings around. Because ASIHttpRequest performs SetDidFinish selector on the main thread my calls performSelectorOnMainThread weren't doing anything. I changed my initial call for the DataSynchronizer to the main thread and added changed the DidFinish method to:
- (void)parseDataInBackground:(ASIHTTPRequest *)request {
[NSThread detachNewThreadSelector:#selector(parseResult:) toTarget:self withObject:request];
Which then makes the parse method run on separate thread (since its the bulk of the processing and now performOnMainThread works without issue.
NSURL *URL = [NSURL URLWithString:#"http://www.stackoverflow.com"];
NSURLRequest *request = [NSURLRequest requestWithURL:URL];
NSURLConnection *connection = [NSURLConnection connectionWithRequest:request delegate:self];
With code as simple as that, I can load a webpage in my application. I don't have to worry about retaining or releasing the NSURLConnection, it will autorelease when it's done loading.
I'm creating some sort of wrapper around NSURLConnection, JSONConnection. It allows me to load a JSON value from a webpage and automatically parse that in a NSDictionary. Right now, I have to use it like this:
JSONConnection *tempJSONConnection = [[JSONConnection alloc] initWithURLString:#"http://www.stackoverflow.com" delegate:self];
self.JSONConnection = tempJSONConnection;
[tempJSONConnection release];
Then, when it's done loading, I call self.JSONConnection = nil;.
What I want, is to do this:
JSONConnection *connection = [JSONConnection connectionWithURLString:#"http://www.stackoverflow.com" delegate:self];
I know how to create this method. I just don't know how to keep connection alive when the runloop is finished and the autorelease pool is drained, and make sure connection is deallocated when it's done loading. In other words, I don't how to duplicate the exact behavior of NSURLConnection.
To all intents and purposes, from the outside, NSURLConnection effectively retains itself. This was either done by sending
[self retain];
when starting the connection and then
[self release];
when finished and after informing the delegate; or it was done by placing itself in a pool of currently open connections and removing it from that pool on completion.
You don't actually have to do any of this. NSURLConnection retains its delegate, so your JSON connection class should create an NSURLConnection passing itself as the NSURLConnection's delegate. That way it will live at least as long as the NSURLConnection. It should parse the JSON into a dictionary in the method -connectionDidFinishLoading: and pass the dictionary on to its delegate before returning. After returning the NSURLConnection will release and possibly deallocate itself and also release your JSON connection.
Someone should trac connection's live time in any case. It is a bad solutions to trac it inside the connection.
IMO the right way to do it is use singleton class to perform connections
#protocol JSONDataProviderDelegate <NSObject>
- (void) JSONProvider:(JSONDataProvider*) provider didLoadJSON:(JSONObject*) object;
- (void) JSONProvider:(JSONDataProvider*) provider didFainWithError:(NSError*) error;
#end
#interface JSONDataProvider : NSObject
+ (void) provideJSON:(NSURL*) url delegate:(id<JSONDataProviderDelegate>) delegate;
+ (void) removeDelegate:(id<JSONDataProviderDelegate>delegate);
#end
Usage:
- (void) onSomeEvent
{
[JSONDataProvider provideJSON:[NSURL URLWithString:#"http://example.com/test.json"] delegate:self];
}
- (void) JSONProvider:(JSONDataProvider*) provider didLoadJSON:(JSONObject*) object
{
NSLog(#"JSON loaded: %#", object);
}
- (void) dealloc
{
[JSONDataProvider removeDelegate:self];
[super dealloc];
}