I have a tableview which gets filled by a StreamingXMLParser (https://github.com/AlanQuatermain/aqtoolkit).
When I run my app, the tableView appears empty.
First I thought that my tableView didn't show anything until the async xml parser was ready, but if I start to scroll during the parsing the view is suddenly filled.
My code is based on ParserExample (https://github.com/AlanQuatermain/ParserExample) and the parser is called using the same method as the example:
[parser parseAsynchronouslyUsingRunLoop: [NSRunLoop currentRunLoop]
mode: NSDefaultRunLoopMode
notifyingDelegate: self
selector: #selector(parser:completedOK:)
context: NULL]
I think my problem is that my async task is taking up too much processing power.
Who has experience with the StreamingXMLParser and can help me out?
How can I fix my app so the tableView has more priority than the xml parsing ?
The problem can be simulated by downloading the example project and inserting
[NSThread sleepForTimeInterval:0.2];
After the [self.managedObjectContext save: NULL]; statement in the endPost method of the parserDelegate.
I've been able to circumvent the problem by calling the synchronous method [parser parse] via a small utility called MBProgressHUD Created by Matej Bukovinski.
The MBProgressHUD now calls the parsing method async & fixes my problem. (And gives a nice indicator).
I think the problem is in your parsing. Because when you parse some tags they have some empty or \n string so the first few have empty rows. One more thing that can happen is that the response from the server is coming too late. That's why it takes so much time.
You should place some break points and then check each data.
Related
I'm making an iOS 6 program which downloads JSON data from a website and displays it in a table view. I added a pull to refresh method witch works fine. I can go in the settings view controller (secondViewController) and change the address, everything works. Then, I use the pull to refresh method and my tableView is reloaded. But if I reload 3 times AFTER changing the address, my app crashes. I get this error :
*** Terminating app due to uncaught exception 'NSRangeException',
reason: '*** -[__NSArrayM objectAtIndex:]: index 10 beyond bounds for empty array'
*** First throw call stack:
(0x1ca1012 0x10dee7e 0x1c430b4 0x3084 0xdd8fb 0xdd9cf 0xc61bb 0xd6b4b 0x732dd 0x10f26b0 0x229dfc0 0x229233c 0x2292150 0x22100bc 0x2211227 0x22bb333 0x22bb75f 0x1c60376 0x1c5fe06 0x1c47a82 0x1c46f44 0x1c46e1b 0x1bfb7e3 0x1bfb668 0x22ffc 0x1fbd 0x1ee5)
libc++abi.dylib: terminate called throwing an exception
What am I doing wrong ? And how can I fix that problem ? Thanks for your help !
The key design consideration that leaps out is that your retreiveData method is clearly updating the model (the citiesArray) asynchronously, which means that any interaction with the tableview while this is taking place may fail. You should never asynchronously update the actual citiesArray itself. The update to that array should happen in the main queue.
You should change retrieveData to not touch the existing citiesArray, but rather create and return a new array, and then, in the code you dispatch back to the main queue, only then replace the existing citiesArray and call reloadData, something like:
- (void)refresh:(UIRefreshControl *)refreshControl {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSArray *newCitiesArray = [self retreiveData];
dispatch_async(dispatch_get_main_queue(), ^{
if (newCitiesArray) {
// you presumably only want to reload the data if `retrieveData` was successful
citiesArray = newCitiesArray
[myTableView reloadData];
}
[refreshControl endRefreshing];
});
});
}
Clearly, this will involve some changes to retrieveData, too, but hopefully that's self explanatory. If not, update your question with that code, and we can make further suggestions. But we really shouldn't need to go there, as I suspect you understand the change that needs to take place there.
There are other, more subtle issues you might want to tackle, too, such as thinking about whether you really want to use a global queue, which is concurrent (e.g. if you hit refresh while the previous refresh going, do you really want two queries going on concurrently with your server ... because you dispatch the updates back to the main queue you won't crash, but it's inefficient, you're not guaranteed the order that they'll complete, etc.). You might also want to use NSOperationQueue in which you can write code to permit the cancellation of previous requests, etc.
But all of this is a little complicated and is of secondary concern to your main issue, the crashing. Refactoring the retrieveData code to ensure you don't touch citiesArray, itself, as outlined above, should address that.
I am working on a web-services data processing app and I am trying to make the app run as quickly as possible. When a certain 3 finger pan gesture is performed, I call a method that sends updated information off to the server to get a new batch of images to update the existing ones with.
So lets say there are 15 images in an array, I filter through them with a 2 finger gesture, and then if I want to change something about them, I can do the 3 finger gesture, and I get that same set back, just tweaked a bit (contrast/brightness, etc.).
Is what I want though is to be able to update the imageView that is displaying the images after the first image has been retrieved, so as to give the user a feel for what the rest in the series are going to look like. But no matter what I try, and no matter how many different threads I try and implement, I can't get the imageView to update before the entire download is complete. Once the batch download is done (which is handled on a separate thread) the imageView updates with the new images and everything is great.
The first step in the process is this:
if(UIGestureRecognizerStateEnded == [recognize state]){
[self preDownload:windowCounter Level:levelCounter ForPane:tagNumber];// Where this method is what gets the first image, and tries to set it to the imageView
[self downloadAllImagesWithWL:windowCounter Level:levelCounter ForPane:tagNumber]; //And this method goes and gets all the rest of the images
}
This is my preDownload method:
-(void)preDownload:(int)window Level:(int)level ForPane:(int) pane{
int guidIndex = [[globalGuids objectAtIndex:pane] intValue];
UIImage *img = [DATA_CONNECTION getImageWithSeriesGUID:[guids objectAtIndex:guidIndex] ImageID:counter Window:window Level:level];
if(pane==0){
NSLog(#"0");
[imageView3 setImage:img];
}else if(pane==1){
NSLog(#"1");
[imageView31 setImage:img];
}else if(pane==2){
NSLog(#"2");
[imageView32 setImage:img];
}else if(pane==3){
NSLog(#"3");
[imageView33 setImage:img];
}
}
So by separating this out into two different methods (there are no threads being implemented at this point, these methods are being called before all that) I was thinking that after the preDownload method completed, that the imageView would update, and then control would continue on down into the downloadAllImagesWithWL method, but that doesn't appear to be the case.
Am I missing something simple here? What can I do to update my GUI elements before that second method is through running?
You are right. However the viewn won't refresh until your code reaches runloop. You can do 2 things:
Make your downloadAllImagesWithWL method async, so it will return after you called it, your main thread reaches runloop, gui updates, and the download method will tell your logic through a callback when its done.
OR
A simplier hackier (and bad) solution would be to run runloop for some time before you call your download method. Something like this: [[NSRunloop currentRunLoop] runUnitlDate: [Date dateWithTimeIntervalSinceNow: 0.1]]; It will run runloop for 0.1 second.
When the image is set, the image view will mark itself as needing display. The actual display won't occur until the beginning of the next run loop. In OS X, you can use -display to draw the view immediately, but I don't think Apple created a public method to do this on iOS. However, if the next method simply creates the background thread, then it will return quickly and the display update will probably occur before the thread finishes.
I have an application that downloads an xml file, parses the file, and creates core data objects while doing so. In the parse code I have a function called 'emptydatacontext' that removes all items from Core Data before creating replacements items from the xml data. This method looks like this:
-(void) emptyDataContext
{
NSFetchRequest * allCon = [[NSFetchRequest alloc] init];
[allCon setEntity:[NSEntityDescription entityForName:#"Condition" inManagedObjectContext:managedObjectContext]];
NSError * error = nil;
NSArray * conditions = [managedObjectContext executeFetchRequest:allCon error:&error];
DebugLog(#"ERROR: %#",error);
DebugLog(#"RETRIEVED: %#", conditions);
[allCon release];
for (NSManagedObject * condition in conditions) {
[managedObjectContext deleteObject:condition];
}
// Update the data model effectivly removing the objects we removed above.
//NSError *error;
if (![managedObjectContext save:&error]) {
DebugLog(#"%#", [error domain]);
}
}
The first time this runs it deletes all objects and functions as it should - creating new objects from the xml file. I created a 'update' button that starts the exact same process of retrieving the file the proceeding with the parse & build. All is well until its time to delete the core data objects. This 'deleteObject' call creates a "EXC_BAD_ACCESS" error each time. This only happens on the second time through.
Captured errors return null. If I log the 'conditions' array I get a list of NSManagedObjects on the first run. On the second this log request causes a crash exactly as the deleteObject call does.
I have a feeling it is something very simple I'm missing or not doing correctly to cause this behavior. The data works great on my tableviews - its only when trying to update I get the crashes.
I have spent days & days on this trying numerous alternative methods. Whats left of my hair is falling out. I'd be willing to ante up some cash for anyone willing to look at my code and see what I'm doing wrong. Just need to get past this hurdle.
Thanks in advance for the help!
Did you save the context after removing the objects in the for loop? Be aware that deleteObject: does not delete the object immediately, it simply schedule it for deletion when changes are committed, i.e., when you save the context.
EDIT: Your problem may be related to how you present your data to the user on your table view. Without additional code is difficult to tell exactly (are you using NSFetchedResultsController or not?), but my guess is that the interaction between deleting the data and showing them on the table is not correct. Probably, what is happening is that your table is told to visualize your data, but then, when you delete them, you are not updating correctly the table.
Wow, so after a few days of testing I went down a path that led me to tracking down Zombies & memory mgmt. This was a situation where the errors I was recieving were leftover from issues in another area. When parsing the data and placing it into Core Data I released an object that was to be autoreleased. So any subsequent calls to that item within core data (save, deletec, etc) caused a crash. Thank you all for your help and I vow to pay closer attention with my memory mgmt calls.
I am trying to create class that will handle multiple downloads at same time (I need to download a lot of small files) and I have problems with "disappearing" connections.
I have function addDonwload that adds url to list of urls to download, and checks if there is free download slot available. If there is one it starts download immediately. When one of downloads finishes, I pick first url form list and start new download.
I use NSURLConnection for downloading, here is some code
- (bool) TryDownload:(downloadInfo*)info
{
int index;
#synchronized(_asyncConnection)
{
index = [_asyncConnection indexOfObject:nullObject];
if(index != NSNotFound)
{
NSLog(#"downloading %# at index %i", info.url, index);
activeInfo[index] = info;
NSURLRequest *request = [NSURLRequest requestWithURL:info.url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:15];
[_asyncConnection replaceObjectAtIndex:index withObject:[[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:TRUE]];
//[[_asyncConnection objectAtIndex:i] scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
return true;
}
}
return false;
}
- (void)connectionDidFinishLoading:(NSURLConnection*)connection
{
[self performSelectorOnMainThread:#selector(DownloadFinished:) withObject:connection waitUntilDone:false];
}
- (void)DownloadFinished:(id)connection
{
NSInteger index = NSNotFound;
#synchronized(_asyncConnection)
{
index = [_asyncConnection indexOfObject:(NSURLConnection*)connection];
}
[(id)activeInfo[index].delegate performSelectorInBackground:#selector(backgroundDownloadSucceededWithData:) withObject:_data[index]];
[_data[index] release];
[activeInfo[index].delegate release];
#synchronized(_asyncConnection)
{
[[_asyncConnection objectAtIndex:index] release];
[_asyncConnection replaceObjectAtIndex:index withObject:nullObject];
}
#synchronized(downloadQueue)
{
[downloadQueue removeObject:activeInfo[index]];
[self NextDownload];
}
}
- (void)NextDownload
{
NSLog(#"files remaining: %i", downloadQueue.count);
if(downloadQueue.count > 0)
{
if([self TryDownload:[downloadQueue objectAtIndex:0]])
{
[downloadQueue removeObjectAtIndex:0];
}
}
}
_asyncConnection is my array of download slots (NSURLConnections)
downloadQueue is list of urls to download
What happens is, at the beginning everything works ok, but after few downloads my connections start to disappear. Download starts but connection:didReceiveResponse: never gets called. There is one thing in output console that I don't understand I that might help a bit. Normaly there is something like
2010-01-24 21:44:17.504 appName[3057:207]
before my NSLog messages. I guess that number in square brackets is some kind of app:thread id? everything works ok while there is same number, but after some time, "NSLog(#"downloading %# at index %i", info.url, index);" messages starts having different that second number. And when that happens, I stop receiving any callbacks for that urlconnection.
This has been driving me nuts as I have strict deadlines and I can't find problem. I don't have many experiences with iphone dev and multithreaded apps. I have been trying different approaches so my code is kinda messy, but I hope you will see what I am trying to do here :)
btw is anyone of you know about existing class/lib I could use that would be helpful as well. I want parallel downloads with ability o dynamically add new files to download (so initializing downloader at the beginning with all urls is not helpful for me)
You've got a bunch of serious memory issues, and thread synchronization issues in this code.
Rather than go into them all, I'll ask the following question: You are doing this on a background thread of some kind? Why? IIRC NSURLConnection already does it's downloads on a background thread and calls your delegate on the thread that the NSURLConnection was created upon (e.g., your main thread ideally).
Suggest you step back, re-read NSURLConnection documentation and then remove your background threading code and all the complexity you've injected into this unnecessarily.
Further Suggestion: Instead of trying to maintain parallel positioning in two arrays (and some sketchy code in the above relating to that), make one array and have an object that contains both the NSURLConnection AND the object representing the result. Then you can just release the connection instance var when the connection is done. And the parent object (and thus the data) when you are done with the data.
I recommend that you take a look at this:
http://allseeing-i.com/ASIHTTPRequest/
It's a pretty sophisticated set of classes with liberal licensing terms (free too).
It may provide a lot of the functionality that you are wanting.
This snippet can be the source of the bug, you release the object pointed to by the activeInfo[index].delegate pointer right after issuing async method call on that object.
[(id)activeInfo[index].delegate performSelectorInBackground:#selector(backgroundDownloadSucceededWithData:) withObject:_data[index]];
[_data[index] release];
[activeInfo[index].delegate release];
Do you use connection:didFailWithError: ? There may be a timeout that prevents the successful download completion.
Try to get rid of the #synchronized blocks and see what happens.
The string inside the square brackets seems to be thread identifier as you guessed. So maybe you get locked in the #synchronized. Actually, I don't see a reason for switching thread - all the problematic code should run in the main thread (performSelectorOnMainThread)...
Anyhow, there is no need to use both the #synchronized and the performSelectorOnMainThread.
BTW, I didn't see the NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self]; line. Where do you initiate the connection?
As for the parallel downloads - I think that you can download more than one file in a time with the same code that you use here. Just create a separate connection for each download.
Consider just keeping a download queue along with a count of active connections, popping items off the top of the queue when downloads complete and a slot becomes free. You can then fire off NSURLConnection objects asynchronously and process events on the main thread.
If you find that your parallel approach prohibits doing all of the processing on the main thread, consider having intermediary manager objects between your main thread download code and NSURLConnection. Using that approach, you'd instantiate your manager and get it to use NSURLConnection synchronously on a background thread. That manager then completely deals with the downloading and passes the result back to its main thread delegate using a performSelectorOnMainThread:withObject: call. Each download is then just a case of creating a new manager object when you've a slot free and setting it going.
i have made one list of images + respective data in tableview.
it takes long time while loading
i want to make multithreading two methods
1> parsing of data
2> parsing of images
i want to execute parsing of data first after that i can select any of rows listed even though images not been loaded(/parsed) because the images is parsed after the parsing of data and it takes long time.
from where should i call these both the methods.
and how enable the selection on row after parsing of the data...
how to do multithread both the methods
waiting for your great responce
Thanking in advance
You likely don't want to use NSThreads - at least not directly.
What you do is subclass NSOperation.
There are a few ways to do what you have in mind. If you know the total number of rows in your table right from the start, then things are simpler:
Make a subclass of NSOperation called MyParseDataOperation. Then make one MyParseDataOperation for each row in your table. When the operation is done, you need to message your main thread with the resulting data.
Code below is full of errors, incomplete. etc.
ie in your MyParseDataOperation class:
MyParseDataOperation
-(id)initWithStuff:(NSURL*)stuff forTableRow:(int)row;
{
blah blah -
// here is where I make sure I have all the data I need for main() which is called in the background on some random thread at some future time.
}
-(void)main;
{
// use data like Urls, file names, etc passed in to the initWithStuff method
get stuff
parse stuff
// ok now you have the data
NSMutableDictionary* parsedData = [NSMutableDictionary dictionary];
[parsedData setObject:[NSNumber numberWithInt:row] forKey:#"row"];
[parsedData setObject:stuff i figured out forKey:#parsed];
[tableDataSource performSelectorOnMainThread:#selector(dataParsed) withObject:parsedData];
}