The following are methods that I am using to retrieve data from a server while displaying a UIActivityIndicator. I'm trying to put these methods in the app delegate and then call them from other classes, but I don't know how to return my JSONData. Can anybody help with this?
-(void)startProcess:(NSString *)buildURL{
UIActivityIndicatorView *aInd = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActionSheetStyleBlackTranslucent];
[aInd setFrame:CGRectMake(0, 0, 50, 50)];
[aInd startAnimating];
// then call the timeCOnsumingmethod in separate thread.
[NSThread detachNewThreadSelector:#selector(getData:) toTarget:self withObject:buildURL];
}
- (void)getData:(NSString *)buildURL{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
// Query our database for a restaurant's menus
NSURL *url = [NSURL URLWithString:buildURL];
NSError *e;
NSString *jsonreturn = [[NSString alloc] initWithContentsOfURL:url encoding:NSUTF8StringEncoding error:&e];
NSData *jsonData = [jsonreturn dataUsingEncoding:NSUTF32BigEndianStringEncoding];
// NSError *error = nil;
[self performSelectorOnMainThread:#selector(endProcess:) withObject:jsonData waitUntilDone:YES];
[pool release];
//return jsonData;
}
- (IBAction)endProcess:(NSData *)jsonData{
// ??????????
return jsonData;
}
Not sure why got downvoted but your approach is all wrong. Here's what you want to do:
Add the UIActivityIndicatorView
Use NSURLConnection to asynchronously retrieve the data
Use NSJSONSerialization to decode the received JSON into a NSDictionary or NSArray
Remove the UIActivityIndicatorView
Your best bet would be to implement this as a separate class that takes a delegate object. You could implement a delegate protocol to indicate states like 'started network activity' (which your delegate could use to add a spinner view), and 'received data' (which would pass the decoded object back to the delegate - the delegate could then remove the spinner).
One of the benefits of this approach is you can easily set it up so that the connection/request is canceled when the object deallocs. Then you just store the request object as a property on your delegate, and when your delegate goes away, it deallocs the request, which cancels/cleans up properly.
Related
I've got 2 classes, MPRequest and MPModel.
The MPModel class has a method to lookup something from the core data store, and if not found, creates an MPRequest to retrieve it via a standard HTTP request (The method in MPModel is static and not and instance method).
What I want is to be able to get a progress of the current HTTP request. I know how to do this, but I'm getting a little stuck on how to inform the view controller. I tried creating a protocol, defining a delegate property in the MPRequest class, altering the method in MPModel to accept this delegate, and in turn passing it to the MPRequest when it is created.
This is fine, however ARC is then releasing this delegate whilst the request is running and thus doesn't do what I want. I'm trying to avoid making my delegate object a strong reference in case it throws up any reference cycles but I don't know any other way of doing this.
To start the request, from my view controller I'm running
[MPModel findAllWithBlock:^(NSFetchedResultsController *controller, NSError *error) {
....
} sortedBy:#"name" ascending:YES delegate:self]
Inside the findAllWithBlock method, I have
MPRequest *objRequest = [MPRequest requestWithURL:url];
objRequest.delegate = delegate;
[objRequest setRequestMethod:#"GET"];
[MPUser signRequest:objRequest];
[objRequest submit:^(MPResponse *resp, NSError *err) {
...
}
And in the MPRequest class I have the following property defined :
#property (nonatomic, weak) NSObject<MPRequestDelegate> *delegate;
Any ideas or suggestions?
As requested, here is some more code on how things are being called :
In the view controller :
[MPPlace findAllWithBlock:^(NSFetchedResultsController *controller, NSError *error) {
_placesController = controller;
[_listView reloadData];
[self addAnnotationsToMap];
[_loadingView stopAnimating];
if (_placesController.fetchedObjects.count > 0) {
// We've got our places, but if they're local copies
// only, new ones may have been added so just update
// our copy
MPSyncEngine *engine = [[MPSyncEngine alloc] initWithClass:[MPPlace class]];
engine.delegate = self;
[engine isReadyToSync:YES];
[[MPSyncManager sharedSyncManager] registerSyncEngine:engine];
[[MPSyncManager sharedSyncManager] sync];
}
} sortedBy:#"name" ascending:YES delegate:self];
Here, self is never going to be released for obvious reasons, so I don't see how this is the problem.
Above, MPPlace is a subclass of MPModel, but the implementation of the findAllWithBlock:sortedBy:ascending:delegate: is entirely in MPModel
The method within MPModel looks like this
NSManagedObjectContext *context = [[MPCoreDataManager sharedInstance] managedObjectContext];
[context performBlockAndWait:^{
__block NSError *error;
NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:NSStringFromClass([self class])];
[request setSortDescriptors:#[[[NSSortDescriptor alloc] initWithKey:key ascending:asc]]];
NSFetchedResultsController *controller = [[NSFetchedResultsController alloc] initWithFetchRequest:request
managedObjectContext:context
sectionNameKeyPath:nil
cacheName:nil];
[controller performFetch:&error];
if (!controller.fetchedObjects || controller.fetchedObjects.count == 0) {
// Nothing found or an error, query the server instead
NSString *url = [NSString stringWithFormat:#"%#%#", kMP_BASE_API_URL, [self baseURL]];
MPRequest *objRequest = [MPRequest requestWithURL:url];
objRequest.delegate = delegate;
[objRequest setRequestMethod:#"GET"];
[MPUser signRequest:objRequest];
[objRequest submit:^(MPResponse *resp, NSError *err) {
if (err) {
block(nil, err);
} else {
NSArray *objects = [self createListWithResponse:resp];
objects = [MPModel saveAllLocally:objects forEntityName:NSStringFromClass([self class])];
[controller performFetch:&error];
block(controller, nil);
}
}];
} else {
// Great, we found something :)
block (controller, nil);
}
}];
The delegate is simply being passed on to the MPRequest object being created. My initial concern was that the MPRequest object being created was being released by ARC (which I guess it probably is) but it didn't fix anything when I changed it. I can't make it an iVar as the method is static.
The submit method of the request looks like this :
_completionBlock = block;
_responseData = [[NSMutableData alloc] init];
[self prepareRequest];
[self prepareRequestHeaders];
_connection = [[NSURLConnection alloc] initWithRequest:_urlRequest
delegate:self];
And when the app starts downloading data, it calls :
[_responseData appendData:data];
[_delegate requestDidReceive:(float)data.length ofTotal:_contentLength];
Where _contentLength is simply a long storing the expected size of the response.
Got it working. It was partly an issue with threading, where the core data thread was ending before my request, me looking at the output from a different request entirely, and the way ARC handles memory in blocks.
Thanks for the help guys
I'm pretty sure I know what is happening, however I want to know if there is a nice way of stopping it from happening.
Basically, I have a class method which looks something up from the core data store, and if nothing exists attempts to fetch it from a web server. The core data lookup and request are performed in the managed object contexts performBlock method.
I have the following block of code:
[context performBlock:^{
__block NSError *error;
NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:NSStringFromClass([self class])];
[request setSortDescriptors:#[[[NSSortDescriptor alloc] initWithKey:key ascending:asc selector:#selector(caseInsensitiveCompare:)]]];
NSFetchedResultsController *controller = [[NSFetchedResultsController alloc] initWithFetchRequest:request
managedObjectContext:context
sectionNameKeyPath:keyPath
cacheName:nil];
[controller performFetch:&error];
if (!controller.fetchedObjects || controller.fetchedObjects.count == 0) {
// Nothing found or an error, query the server instead
NSString *url = [NSString stringWithFormat:#"%#%#", kMP_BASE_API_URL, [self baseURL]];
MPRequest *objRequest = [MPRequest requestWithURL:url];
[objRequest setRequestMethod:#"GET"];
[MPUser signRequest:objRequest];
[objRequest submit:^(MPResponse *resp, NSError *err) {
if (err) {
block(nil, err);
} else {
NSArray *objects = [self createListWithResponse:resp];
objects = [MPModel saveAllLocally:objects forEntityName:NSStringFromClass([self class])];
[controller performFetch:&error];
block(controller, nil);
}
}];
} else {
// Great, we found something :)
block (controller, nil);
}
}];
What is happening, is that the MPRequest object is created, and fired, however the submit method triggers an asynchronous request and thus returns almost instantly. I assume ARC is then releasing the MPRequest object. When the request is performed, the internal request object's delegate no longer exists, as ARC has released it (the MPRequest object is the delegate for the internal request it has). Because of this, the block that the submit method is provided with isn't called.
Is there any way I can prevent ARC for doing this without making the request synchronous?
Edit
The submit method of MPRequest looks like this
_completionBlock = block;
_responseData = [[NSMutableData alloc] init];
[self prepareRequest];
[self prepareRequestHeaders];
_connection = [[NSURLConnection alloc] initWithRequest:_urlRequest
delegate:self];
[self requestStarted];
Your MPRequest object needs to keep itself alive while the connection is running. The simplest way to do this is probably to retain itself when the connection is started, and then release itself after it calls the completion block. Under ARC, the simplest way to do this is
CFRetain((__bridge CFTypeRef)self);
and
CFRelease((__bridge CFTypeRef)self);
Conceptually, the run loop keeps the request alive. This is how NSURLConnection operates. But since MPRequest isn't actually attached to the run loop, it's just a wrapper around NSURLConnection, you need to do some work to keep it alive for the same period of time.
Also note that the NSURLConnection needs to be added to the appropriate runloop. The convenience method will add it to the current thread's runloop, but if you're in a background queue, that's not going to work. You can use something like
_connection = [[NSURLConnection alloc] initWithRequest:request delegate:delegate startImmediately:NO];
[_connection scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
set this MPRequest outside of the context performBlock:^{...} like so:
__strong MPRequest = // allocate or set the MPRequest.
[context performBlock:^{...}
Now once the performBlock is finished, the MPRequest will not have been released, and still be set to whatever variable you designated it to in the __strong clause.
I'm kind of a newbie in objective-c and I'm having issues when I call a NSArray from other class. I have a class which handles the parsing of a XML feed and another to manage the UItableview stuff. It's weird because when it's done synchronously (using NSXMLParser methods) all data is shown in the table, but when I use the NSURLConnection to make it asynchronous it parses all the data but the array is empty when it's called. If I call NSLog it shows all data contained the newsStories array when the data is being parsed, but somehow its deleted when I call it.
On the parser class I have and all the methods of the NSXMLParser:
- (void)parseXMLFileAtUrl:(NSString *)URL {
data = [[NSMutableData alloc] init];
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:URL] cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];
NSURLConnection *connection = [[NSURLConnection alloc]initWithRequest:request delegate:self];
if (connection) {
data = [[NSMutableData alloc]init];
}
[connection release];
}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
//Reset the data as this could be fired if a redirect or other response occurs
[data setLength:0];
}
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)_data
{
//Append the received data each time this is called
[data appendData:_data];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
//Start the XML parser with the delegate pointing at the current object
_parser = [[NSXMLParser alloc] initWithData:data];
newsStories = [[NSMutableArray alloc] init];
[_parser setDelegate:self];
[_parser setShouldProcessNamespaces:NO];
[_parser setShouldReportNamespacePrefixes:NO];
[_parser setShouldResolveExternalEntities:NO];
[_parser parse];
}
And this is how I call the array:
-(BOOL) loadData{
NSString *latestUrl = [[NSString alloc] initWithString:feed];
if ([latestArray count] == 0) {
news = [[news_parser alloc]init];
[news parseXMLFileAtUrl:latestUrl];
[self setArray:news.newsStories];--- here it says null for Array and for newsItems
}
[latestUrl release];
return YES;
}
- (void)viewDidLoad
{
[super viewDidLoad];
array = [[NSMutableArray alloc]init];
_News.rowHeight =85;
[self loadData];
[self._News reloadData];
}
Any help would be appreciated, thanks guys!
Regards.
... Do you understand what asynchronous means? It means that your function will return and the connection will continue, making the callbacks when it is ready. The way you have this coded up, you start the connection and then immediately try to use the data -- it isn't there yet! You need to wait until after connectionDidFinishLoading before you try to use the array.
Do some more research on what exactly it means to be asynchronous; it seems you're not understanding that.
Edit
Let me clarify, since you seem to have missed my point. Your viewDidLoad function finishes long before your connectionDidFinishLoading callback gets called, and so of course the newsStories array is not there yet. When you call:
[news parseXMLFileAtUrl:latestUrl];
in the loadData function, that doesn't stop and wait for the connection to return; if it were synchronous, it would, but asynchronous does not. (Hence I ask you to research what asynchronous actually means, which apparently you still have not done). Since that call returns and then you immediately try to use the loaded data (long before the connectionDidFinishLoading is called) you naturally don't have any data in there.
From Apple's docs:
Mutable objects are generally not thread-safe. To use mutable objects
in a threaded application, the application must synchronize access to
them using locks. (For more information, see “Atomic Operations”). In
general, the collection classes (for example, NSMutableArray,
NSMutableDictionary) are not thread-safe when mutations are concerned.
That is, if one or more threads are changing the same array, problems
can occur. You must lock around spots where reads and writes occur to
assure thread safety.
Reading this might help you out. Not totally sure if that is what is going on in your app but it looks like a good place to start.
I'm working on my first JSON example in objective-c and came across this great tutorial that I'm trying to reproduce. Along the way I decided to push the JSON returned into my already working tableView (just to ensure I could do something w/ the data in the view).
- (void)viewDidLoad {
[super viewDidLoad];
responseData = [[NSMutableData data] retain];
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:#"http://www.unpossible.com/misc/lucky_numbers.json"]];
[[NSURLConnection alloc] initWithRequest:request delegate:self];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
[connection release];
NSString *responseString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];
[responseData release];
NSArray *luckyNumbers = [responseString JSONValue];
NSMutableString *text = [NSMutableString stringWithString:#"Nums "];
for (int i = 0; i < [luckyNumbers count]; i++)
[text appendFormat:#"%#", [luckyNumbers objectAtIndex:i]];
self.movies = [[NSArray alloc] initWithObjects:#"First", text, #"Last", nil];
}
What I've found is that when I set the array in "connectionDidFinishLoading" it shows up as nothing in the running application - yet if I set this directly in the "viewDidLoad" method with 3 simple string values it shows up fine.
When I debug the running application I see the JSON response and the string looks valid (no issues that I can see).
Is the datasource for my tableView already set in stone before this "connectionDidFinishLoading" method or did I miss something?
Your UITableView will call upon its DataSource for data once initially, presumably sometime after viewDidLoad. After that first load, it will only request data as it needs it (i.e. as you scroll to different cells.) If you want to make it refresh its contents when your data is ready (like after you've received your URL data), call [tableView reloadData].
My initial question was solved by this solution:
At the end of my "connectionDidFinishLoading" method I call a method on the appDelegate called "jsonFinished".
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
//do all the json work and set the array that I'm using as my datasource
self.movies = [[NSArray alloc] initWithObjects:#"First", "Last", nil];
[appDelegate jsonFinished]; //have the app delegate do the refresh call back
}
Then inside the appDelegate I simply provide an implementation for the "jsonFinished" method that does a refresh of the UITableView
- (void)jsonFinished
{
moviesController.refreshDisplay;
}
And in the "refreshDisplay" method I do the reloadData on the tableView
- (void)refreshDisplay
{
[moviesTableView reloadData];
}
And now after the data is loaded the appDelegate fires off the method that reloads the data for tableView
CSURLCache is designed to cache resources for offline browsing, as NSURLCache only stores data in-memory.
If cachedResponse is autoreleased before returning the application crashes, if not, the objects are simply leaked.
Any light that could be shed onto this would be much appreciated.
Please note stringByEncodingURLEntities is a category method on NSString.
#interface CSURLCache : NSURLCache {} #end
#implementation CSURLCache
- (NSCachedURLResponse *)cachedResponseForRequest:(NSURLRequest *)request
{
NSString *path = [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:[[[request URL] absoluteString] stringByEncodingURLEntities]];
if ([[NSFileManager defaultManager] fileExistsAtPath:path])
{
NSData *data = [[NSData alloc] initWithContentsOfFile:path];
NSURLResponse *response = [[NSURLResponse alloc] initWithURL:[request URL]
MIMEType:nil
expectedContentLength:[data length]
textEncodingName:nil];
NSCachedURLResponse *cachedResponse = [[NSCachedURLResponse alloc] initWithResponse:response
data:data];
[response release];
[data release];
return cachedResponse;
}
return nil;
}
#end
UPDATE: After submitting a radar to Apple it appears that this is a known issue (Radar #7640470).
- (NSCachedURLResponse *)cachedResponseForRequest:(NSURLRequest *)request
Well, this isn't an alloc, new, or copy method…
… and CSURLCache doesn't hold on to the object anywhere, so it's not owning it.
So, you need to autorelease it.
Of course, that means the object is doomed unless something retains it. Your app crashed because it tried to use the object after the object died.
Run your app under Instruments with the Zombies template. Look at where the app crashes and what it was doing when cachedResponseForRequest: was called. The caller needs to own the object until the time when the application would crash otherwise, and then release it.