I create a object in a function.
-(void) loginAction {
UILoginXML *loginXml = [[UILoginXML alloc] init];
[loginXml start];
[loginXml release]; //mark
}
when the start method was called, it may cost 2 or 3 minutes to parse XML.
the question is whether I can release this object at "mark"?
Thanks a lot!
That depends, is [loinXml start]; a synchronous call? Then it should work just fine, if it's asynchronous it will not.
If it costs you 2-3 minutes to parse, maybe its better to wrap ULoginXML to a class that has this current class as its delegate. Why? Then you can perform the parsing in the background and then send a message back to the delegate when you are done.
If you already parse in a background thread (ULoginXML), then you'll gain loose coupling, and scaleability.
Related
I have a class named "ServerDataLayer" that holds a NSURLConnection, and a NSMutableData that its writing the received HTTP data in to. When the connection finishes, it simply fires a delegate that my caller passed itself as a reference, the method looks like this:
-(void) serverDataLayerResponse:(id)entity
{
if ([entity isMemberOfClass:[LoginResponse class]])
{
LoginResponse *response = (LoginResponse*)entity;
NSLog(#"Error Code: %d", response.errorCode);
NSLog(#"Error Message: %#", response.errorMessage);
NSLog(#"Registered: %c", response.registered);
NSLog(#"AuthToken: %#", response.authToken);
[AppData shared].authToken = response.authToken;
ServerDataLayer *request = [[[ServerDataLayer alloc] initWithServer:_serverUrl delegate:self] autorelease];
[request getPlayerDetails];
//[_server getPlayerDetails];
}
}
Here's my problem...the internal _receivedData and _connection variables are currently in use whilst this delegate method is in progress. I wanted to use my same ServerDataLayer instance to fire another request off "[_server getPlayerDetails]", but the _connection and _receivedData variables internally were getting overwritten and I was getting in to a mess about when to retain/release at the right time.
So my work around was just to instantiate the ServerDataLayer each time I wanted to talk to the server. Now...in the example above, I'm instantiating the request with an 'alloc', and setting an 'autorelease' as I lose scope of this 2nd request. Will this 2nd request stay in memory whilst it's NSURLConnection is busy internally performing the request?
I'm getting a bit lost at this point on how to manage the object references for this kind of process. Any help would be appreciated.
An NSURLConnection, if used via the delegate methods will attach itself as an input to a run loop. However it won't retain its delegate. So your ServerDataLayer would be deallocated (and hopefully remember to cancel the connection). You could use object associations to give your object the same lifecycle as the URL connection, if you were suitably careful about the potential retain loop.
If you use sendAsynchronousRequest:... then you'll probably be fine anyway; assuming you reference self or any instance variable in the completion block then you'll be retained by the block and live for at least as long as it does.
There's really no need to confuse yourself over retain/release any more. Even if ARC isn't an option, you can just declare the relevant instance variables as retain properties within a class extension and use self.property notation to set new values. Retains and releases will be handled for you.
The only caveat is that you should never use dot notation in either your init or dealloc as a special case of the rule that it isn't safe to call methods on a class that's only half instantiated or is half destroyed.
Just use multiple ServerDataLayer instances.
I'm searching for a nice way to perform a selector on the main thread with two parameters
I really like using
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait
method, except now I have two parameters.
So basically I have a delegate which I need to notify when the image is loaded:
[delegate imageWasLoaded:(UIImage *)image fromURL:(NSString *)URLString;
But the method where I do this might be invoked in the background thread, and the delegate will use this image to update the UI, so this needs to be done in the main thread. So I really want the delegate to be notified in the main thread as well.
So I see one option - I can create a dictionary, this way I have only one object, which contains two parameters I need to pass.
NSDictionary *imageData = [NSDictionary dictionaryWithObjectsAndKeys:image, #"image", URLString, #"URLstring", nil];
[(NSObject *)delegate performSelectorOnMainThread:#selector(imageWasLoaded:) withObject: imageData waitUntilDone:NO];
But this approach does not seem right to me. Is there more elegant way to do this? Perhaps using NSInvocation?
Thanks in advance.
Using an NSDictionary to pass multiple parameters is the right way to go about it in this case.
However, a more modern method is to use GCD and blocks, this way you can send messages to an object directly. Also, it looks as if your delegate method might be doing something UI updates; which you are correctly handling on the main thread. With GCD you can do this easily, and asynchronously like this:
dispatch_async(dispatch_get_main_queue(), ^{
[delegate imageWasLoaded:yourImage fromURL:yourString;
});
Replace your performSelector:withObject call with this, and you won't have to mess around with changing your method signatures.
Make sure you:
#import <dispatch/dispatch.h>
to bring in GCD support.
Since you don't have access to GCD, NSInvocation is probably your best choice here.
NSMethodSignature *sig = [delegate methodSignatureForSelector:selector];
NSInvocation *invoke = [NSInvocation invocationWithMethodSignature:sig];
[invoke setTarget:delegate]; // argument 0
[invoke setSelector:selector]; // argument 1
[invoke setArgument:&arg1 atIndex:2]; // arguments must be stored in variables
[invoke setArgument:&arg2 atIndex:3];
[invoke retainArguments];
/* since you're sending this object to another thread, you'll need to tell it
to retain the arguments you're passing along inside it (unless you pass
waitUntilDone:YES) since this thread's autorelease pool will likely reap them
before the main thread invokes the block */
[invoke performSelectorOnMainThread:#selector(invoke) withObject:nil waitUntilDone:NO];
Following method can also be used:
- (id)performSelector:(SEL)aSelector withObject:(id)anObject withObject:(id)anotherObject
As per the docs of this method-
Invokes a method of the receiver on the current thread using the default mode after a delay.
Yes, you've got the right idea: you need to encapsulate all the data you want to pass to the delegate on the main thread into one single object which gets passed along via performSelectorOnMainThread. You can pass it along as a NSDictionary object, or a NSArray object, or some custom Objective C object.
I detach a new NSThread withObject:self so that the thread can callback the main thread as a delegate. However, I also need the new thread to be able to read some values in the parent. With NSThread, I can only pass one object withObject, and I'm using that to pass self because of the delegate methods. Is there a way my new thread can read values from it's parent? Perhaps through the self object that is passed to it?
Here's where I launch the thread:
MulticastDaemon* multicastDaemon = [[MulticastDaemon alloc] init];
[NSThread detachNewThreadSelector:#selector(doWorkWithDelegate:)
toTarget:multicastDaemon
withObject:self];
I want to pass a multicast IP address and port number to the daemon, so he knows what to listen on, but I'm not sure how to get those values to multicastDaemon.
How can multicastDaemon access those values?
Yes, you can access the variables by making them properties and then doing something like this (you don't say what the class is that this call is made from, so I've called it MyClass):
#implementation MulticastDaemon
-(void) doWorkWithDelegate:(MyClass*) cls
{
cls.value1 = 12;
...
}
...
#end
EDIT: Corrected implementation.
You'd better use the subclass of NSOperation and then add it to the NSOperationQueue. You can add any additional parameters to that operation subclass.
There is also another advantage of NSOperation over NSThread. NSOperation and NSOperationQueue are build on top of the GCD and threading is far more optimal then NSThread.
But you can also simply add some properties to your MulticastDaemon.
You can change your MulticastDaemon's interface slightly so that you set the delegate before creating the new thread. Then you free up the withObject: slot to pass something else along. This avoids accessing variables across threads.
Either:
MulticastDaemon* multicastDaemon = [[MulticastDaemon alloc] initWithDelegate:self];
[NSThread detachNewThreadSelector:#selector(doWorkWithInformation:)
toTarget:multicastDaemon
withObject:operatingInfo];
Or
MulticastDaemon* multicastDaemon = [[MulticastDaemon alloc] init];
[multicastDaemon setDelegate:self];
Otherwise, you'll have to create a method that the daemon can call on its delegate that gathers and packages up the information to pass back. In that case, you'll probably have to start worrying about thread safety.
I must be doing something wrong, but the Automatic Reference Counting docs don't give me a hint on what it might be. What I'm doing is calling a method with a block callback from inside a delegate method. Accessing that same delegate from inside the block results in a bad access. The problem is the object I'm passing - loginController which is sending the message to its delegate - is clearly not released, when I don't access it inside the block I can call the method multiple times without an issue. Here's my code:
- (void)loginViewDidSubmit:(MyLoginViewController *)loginController
{
NSString *user = loginController.usernameLabel.text;
NSString *pass = loginController.passwordLabel.text;
__block MyLoginViewController *theController = loginController;
[self loginUser:user withPassword:pass callback:^(NSString *errorMessage) {
DLog(#"error: %#", errorMessage);
DLog(#"View Controller: %#", theController); // omit this: all good
theController = nil;
}];
}
NSZombieEnabled does not log anything and there is no usable stack trace from gdb. What am I doing wrong here? Thanks for any pointers!
Edit:
I figured the problem has a bigger scope - the callback above is called from an NSURLConnectionDelegate method (the block itself is a strong property for that delegate so ARC should call Block_copy()). Do I need to take special measurements in this scenario?
Flow (the loginController stays visible all the time):
loginController
[delegate loginViewDidSubmit:self];
View Delegate
(method shown above calls the loginUser: method, which does something like:)
httpDelegate.currentCallback = callback;
httpDelegate.currentConnection = // linebreak for readability
[[NSURLConnection alloc] initWithRequest:req
delegate:httpDelegate
startImmediately:YES];
NSURLConnectionDelegate
- (void)connection:(NSURLConnection *)aConnection
didFailWithError:(NSError *)error
{
if (NULL != currentCallback) {
currentCallback([error localizedDescription]);
self.currentCallback = NULL;
}
}
And this is where I get the bad access, but ONLY if I access that loginController variable...
Set copy attribute to the property, or just call 'copy' method for the block.
- (void)loginUser:(NSString *)user withPassword:(NSString *)pass callback:(void (^callback)(NSString *))
{
callback = [callback copy];
The actual solution was that I had the block as a strong property, but it should have been a copy property! D'oh!
First "Solution":
I just found a way to prevent the bad access. As shown in my Edit above, the View Delegate forwards the block to the httpDelegate (an instance of another class), which in turn keeps a strong reference to the block. Assigning the block to a temporary variable and forwarding the temporary block variable solves the problem, for whatever reason. So:
This crashes on block execution, as described
httpDelegate.currentCallback = callback;
This works
MyCallbackType aCallback = callback;
httpDelegate.currentCallback = aCallback;
I'll accept this as the answer, if anybody has more insights I'm happy to revise my decision. :)
I figure what is happening there is that the loginController is dead right after calling its delegate. Therefore a crash occurs. Without more information I can think of possible scenarios only:
The block do not retains the loginController object (__block type modifier). If the block is executed asynchronously, the loginController might no longer be available if it was killed elsewere. Therefore, no matter what you want to do with it, you wont be able to access it inside the block and the app will crash. This could happen if the controller is killed after sending loginViewDidSubmit.
I think most likely this could be your situation: The loginController calls its delegate object. The delegate method ends up synchronously invoking the callback block that kills the controller. The controller is expected to be alive after invoking the delegate method. Killing it inside the delegate method, most likely will cause crashes to happen. To make sure this is the problem, simply nil the loginController in the delegate method and put an NSLog statement in the controller after calling the delegate, never mind the block, you will get a crash there.
Perhaps if you paste some code we could help more.
My best.
I am creating instances of a class FlickrImage parsing a Flickr API photos response. The class has a method getLocation that does another API call to get the geolocation:
NSLog(#"getting location for %i",self.ID);
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
OFFlickrAPIRequest *flickrAPIRequest = [[OFFlickrAPIRequest alloc] initWithAPIContext[appDelegate sharedDelegate].flickrAPIContext];
[flickrAPIRequest setDelegate:self];
NSString *flickrAPIMethodToCall = #"flickr.photos.geo.getLocation";
NSDictionary *requestArguments = [[NSDictionary alloc] initWithObjectsAndKeys:FLICKR_API_KEY,#"api_key",self.ID,#"photo_id",nil];
[flickrAPIRequest callAPIMethodWithGET:flickrAPIMethodToCall arguments:requestArguments];
[pool release];
I have implemented the callback method that would catch the response from the API and update the FlickrImage instance with the geolocation data - but it never gets called. Here's where the instances get created:
NSDictionary *photosDictionary = [inResponseDictionary valueForKeyPath:#"photos.photo"];
NSDictionary *photoDictionary;
FlickrImage *flickrImage;
for (photoDictionary in photosDictionary) {
flickrImage = [[FlickrImage alloc] init];
flickrImage.thumbnailURL = [[appDelegate sharedDelegate].flickrAPIContext photoSourceURLFromDictionary:photoDictionary size:OFFlickrThumbnailSize];
flickrImage.hasLocation = TRUE; // TODO this is actually to be determined...
flickrImage.ID = [NSString stringWithFormat:#"%#",[photoDictionary valueForKeyPath:#"id"]];
flickrImage.owner = [photoDictionary valueForKeyPath:#"owner"];
flickrImage.title = [photoDictionary valueForKeyPath:#"title"];
[self.flickrImages addObject:[flickrImage retain]];
[flickrImage release];
[photoDictionary release];
}
The retain is there because I thought it might help solve this but it doesn't - and doesn't the NSMutableArray (flickrImages is a NSMutableArray) retain its members anyway?
EDIT I should add that the getLocation method (first code snippet) is launched in a thread:
[NSThread detachNewThreadSelector:#selector(getLocation) toTarget:self withObject:nil];
Your delegate method is never being called because the request is never being made. When you call callAPIMethodWithGET:, it sets up communications to run asynchronously on the current thread's run loop, then returns immediately. That way you can safely call it on the main thread without blocking.
Because you are calling the method from a thread you created yourself, it does not see the main run loop, but the run loop for your new thread. However, because you never execute the run loop, the messages are never sent, a response is never received, and your delegate is never called.
You could fix this by calling [[NSRunLoop currentRunLoop] run] in your new thread. That will let the work happen. But in this case would be easier to never detach a new thread in the first place. Your program won't block, and you won't have to worry about your delegate method needing to be reentrant.
I've also run into this problem when requesting and parsing XML on a different thread my solution was to do this:
while([[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:start] && !isFinished){
}
Where start = [NSDate dateWithTimeIntervalSinceNow:3]; this is basically a timeout so that it doesn't live forever and isFinished is set to true when my parsing has completed.
I'm not familiar with these flicker API wrappers, but in this code:
NSDictionary *requestArguments = [[NSDictionary alloc] initWithObjectsAndKeys:FLICKR_API_KEY,#"api_key",self.ID,#"photo_id",nil];
Are you certain that both FLICKR_API_KEY, and self.ID are not nil? If either of them is nil, you'll end up with a dictionary that has less items in it than you intend.
Could you post the callback method(s) you have implemented – this could be just down to a simple typo, as it appears OFFlickrAPIRequest won’t do anything if the delegate does not implement the required callback.
Did you also implement flickrAPIRequest:didFailWithError: to see if there was an error returned from the API call?
Okay, I did solve it, with help from some of the suggestions above.
I did remove the extra retain because it did in fact create a memory leak. It did not look right from the outset, so my gut feeling about that is worth something, which is a good thing ;)
I removed the redundant threading because the API call is already asynchronous and does not require an additional thread to be non-blocking. After that, the callback method was being called but I ran into different problems concerning object retention. If interested you might want to check out that question, too
Thanks all.
The setDelegate method of OFFlickrAPIRequest does not retain the delegate like it should. This means you're stuck ensuring that your delegate is alive as long as the request is (or patching the class to properly own its own references).