I've been trying to get a PDF from an NSURL that is changed during a
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
The change in NSURL logs perfectly, but the view is loaded before the app has a chance to act upon that change. Is there a way to delay the reading of the change in URL by simply moving the code to the
viewDidLoad
section, or do I have to drastically change everything? Here's my -(id)init method:
- (id)init {
if (self = [super init]) {
CFURLRef pdfURL = (CFURLRef)[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:appDelegate.baseURL ofType:#"pdf"]];
pdf = CGPDFDocumentCreateWithURL((CFURLRef)pdfURL);
}
return self;
}
When you need to work with network the proven approach is to use asynchronous calls. This is because of the nature of a network connection; it is unpredictable, not always reliable, the time you need to spend to get the result from the server can vary from millisecond to minutes.
I would make a data model class, MyPDFModel, with an asynchronous method, that should run a thread to get the file from the server:
- (void)requestPDFWithURL:(NSURL*)fileURL
{
[NSThread detachNewThreadSelector:#selector(requestPDFWithURLThreaded:) toTarget:self fileURL];
}
- (void)requestPDFWithURLThreaded:(NSURL*)fileURL
{
NSAutoreleasePool* pool = [NSAutoreleasePool new];
// do whatever you need to get either the file or an error
if (isTheFileValid)
[_delegate performSelectorOnMainThread:#selector(requestDidGetPDF:) withObject:PDFFile waitUntilDone:NO];
else
[_delegate performSelectorOnMainThread:#selector(requestDidFailWithError:) withObject:error waitUntilDone:NO];
[pool release];
}
Meanwhile the UI should display an activity indicator.
The MyPDFModelDelegate protocol should have two methods:
- (void)requestDidGetPDF:(YourPDFWrapperClass*)PDFDocument;
- (void)requestDidFailWithError:(NSError*)error;
YourPDFWrapperClass is used to return an autoreleased document.
The delegate can let the UI know that the data has been updated, for example by posting a notification if the delegate is a part of the data model.
This is just an example, the implementation can be different depending on your needs, but I think you will get the idea.
P.S. Delaying an init is a very bad idea.
Related
I'm using Magical Record 2.3.0 beta 5 and I have troubles understanding how to get my NSManagedObjects for the current thread. I have a long running NSOperation where I need my PSPlayer (NSManagedObject).
When I init the NSOperation, I keep an id of my PSPlayer and re-fetch the same object in the operation's main method. According to Apple that the way to do it.
#implementation TAPlayerUpdateOperation
- (instancetype)initWithPlayer:(PSPlayer *)player;
{
self = [super init];
if (self) {
self.playerMD5Id = player.md5Id;
}
}
- (void)main
{
#autoreleasepool {
__block BOOL keepUpdating = YES;
PSPlayer *player = [[PSPlayer MR_findAllWithPredicate:[NSPredicate predicateWithFormat:#"md5Id == %#", self.playerMD5Id]] firstObject];
NSLog(#"player.md5Id = %#", player.md5Id);
// rest of my operation logic
}
}
#end
When I run my app with -com.apple.CoreData.ConcurrencyDebug 1, I get a crash when accessing the property in the NSLog statement.
What is the correct way to get my NSManagedObject so that it is safe for the current thread?
I've pinned the problem down to the following snippet where it crashes as well.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
PSPlayer *player =[[PSPlayer MR_findAll] firstObject];
NSLog(#"player = %#", player.name);
});
cheers,
Jan
You need to ensure that everything is saved and merged before the fetch would work. If you're using MR then it's better to take the managed object and call inContext: on it supplying the other context and have it do the work (it also avoids a predicate).
I expect the crash is because you use player.md5Id instead of self.playerMD5Id so you're accessinh the managed object on the wrong thread.
Following TDD I'm developing an iPad app that downloads some info from the internet and displays it on a list, allowing the user to filter that list using a search bar.
I want to test that, as the user types in the search bar, the internal variable with the filter text is updated, the filtered list of items is updated, and finally the table view receives a "reloadData" message.
These are my tests:
- (void)testSutChangesFilterTextWhenSearchBarTextChanges
{
// given
sut.filterText = #"previous text";
// when
[sut searchBar:nil textDidChange:#"new text"];
// then
assertThat(sut.filterText, is(equalTo(#"new text")));
}
- (void)testSutReloadsTableViewDataAfterChangeFilterTextFromSearchBar
{
// given
sut.tableView = mock([UITableView class]);
// when
[sut searchBar:nil textDidChange:#"new text"];
// then
[verify(sut.tableView) reloadData];
}
NOTE: Changing the "filterText" property triggers right now the actual filtering process, which has been tested in other tests.
This works OK as my searchBar delegate code was written as follows:
- (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText
{
self.filterText = searchText;
[self.tableView reloadData];
}
The problem is that filtering this data is becoming a heavy process that right now is being done on the main thread, so during that time the UI is blocked.
Therefore, I thought of doing something like this:
- (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSArray *filteredData = [self filteredDataWithText:searchText];
dispatch_async(dispatch_get_main_queue(), ^{
self.filteredData = filteredData;
[self.tableView reloadData];
});
});
}
So that the filtering process occurs in a different thread and when it has finished, the table is asked to reload its data.
The question is... how do I test these things inside dispatch_async calls?
Is there any elegant way of doing that other than time-based solutions? (like waiting for some time and expect that those tasks have finished, not very deterministic)
Or maybe I should put my code on a different way to make it more testable?
In case you need to know, I'm using OCMockito and OCHamcrest by Jon Reid.
Thanks in advance!!
There are two basic approaches. Either
Make things synchronous only while testing. Or,
Keep things asynchronous, but write an acceptance test that does resynchronizing.
To make things synchronous for testing only, extract the code that actually does work into their own methods. You already have -filteredDataWithText:. Here's another extraction:
- (void)updateTableWithFilteredData:(NSArray *)filteredData
{
self.filteredData = filteredData;
[self.tableView reloadData];
}
The real method that takes care of all the threading now looks like this:
- (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSArray *filteredData = [self filteredDataWithText:searchText];
dispatch_async(dispatch_get_main_queue(), ^{
[self updateTableWithFilteredData:filteredData];
});
});
}
Notice that underneath all that threading fanciness, it really just calls two methods. So now to pretend that all that threading was done, have your tests just invoke those two methods in order:
NSArray *filteredData = [self filteredDataWithText:searchText];
[self updateTableWithFilteredData:filteredData];
This does mean that -searchBar:textDidChange: won't be covered by unit tests. A single manual test can confirm that it's dispatching the right things.
If you really want an automated test on the delegate method, write an acceptance test that has its own run loop. See Pattern for unit testing async queue that calls main queue on completion. (But keep acceptance tests in a separate test target. They're too slow to include with unit tests.)
Albite Jons options are very good options most of the time, sometime it creates less cluttered code when doing the following. For example if your API has a lot small methods that are synchronised using a dispatch queue.
Have a function like this (it could be a method of your class as well).
void dispatch(dispatch_queue_t queue, void (^block)())
{
if(queue)
{
dispatch_async(queue, block);
}
else
{
block();
}
}
Then use this function to call the blocks in your API methods
- (void)anAPIMethod
{
dispatch(dispQueue, ^
{
// dispatched code here
});
}
You would usually initialise the queue in your init method.
#implementation MyAPI
{
dispatch_queue_t dispQueue;
}
- (instancetype)init
{
self = [super init];
if (self)
{
dispQueue = dispatch_queue_create("myQueue", DISPATCH_QUEUE_SERIAL);
}
return self;
}
Then have a private method like this, to set this queue to nil. It is not part of your interface, the API consumer will never see this.
- (void) disableGCD
{
dispQueue = nil;
}
In your test target you create a category to expose the GCD disabling method:
#interface TTBLocationBasedTrackStore (Testing)
- (void) disableGCD;
#end
You call this in your test setup and your blocks will be called directly.
The advantage in my eyes is debugging. When a test case involves a runloop so that blocks are actually called, the problem is that there has to be a timeout involved. This timeout is usually quite short because you don't want to have tests that last long if the they run into the timeout. But having a short timeout means your test runs into the timeout when debugging.
I am creating an app where in the first view, the user is given the option to log-in or register. In the register view is a UITableViewCell that, when clicked, takes the user to a view containing a UITableView and a UIPickerView. The UITableView is working correctly, but the UIPickerView, which is supposed to dynamically pull the data it is supposed to display using a web call, is showing up but appears completely blank. Putting in a few NSLog statements, I noticed that the methods in the Model that pull the data using AFNetworking are never getting called. I've posted the code below for the UIPickerViewDelegate and UIPickerViewDataSource methods, as well as the method that is supposed to pull the data in the Model. Thanks in advance.
UIPickerViewDelegate
- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row
forComponent:(NSInteger)component {
return [[self.brain classChoicesForSignUp] objectAtIndex:row];
}
UIPickerViewDataSource
- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView {
return 1;
}
- (NSInteger)pickerView:(UIPickerView *)pickerView
numberOfRowsInComponent:(NSInteger)component {
size_t numberOfRows = [self.brain classChoicesForSignUp].count;
NSLog(#"Number of Rows: %#", [[NSNumber numberWithFloat:numberOfRows] stringValue]);
return numberOfRows;
}
SignUpPickerBrain.m
#import "SignUpPickerBrain.h"
#import "AFJSONRequestOperation.h"
#implementation SignUpPickerBrain
#pragma mark - Picker Data
- (NSArray *)classChoicesForSignUp {
NSLog(#"Class choices method called");
// Note that in my code, the actual URL is present here.
NSURL *url = [NSURL URLWithString:#"the URL"];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
AFJSONRequestOperation *operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
NSLog(#"Success!");
NSLog([JSON description]);
} failure:nil];
[operation start];
[operation waitUntilFinished];
NSLog([operation responseJSON]);
return [operation responseJSON];
}
#end
There are a lot of anti-patterns going on in this code sample. I strongly recommend against your current approach, and consider the following points:
Do networking asynchronously, i.e. don't use [operation waitUntilFinished];. Any time you're creating a method that makes a network request, give it a block parameter that can be used as a callback once the results come in.
Store your results in an array property in the controller, or the like, and use that to drive your delegates and datasources. In your current approach, you will be doing a network request every single time a row is displayed (!). So instead, initialize to an empty array, and once the new results are set to that property, reload the data source. One asynchronous request. Easy.
Get rid of SignUpPickerBrain. Either use a proper Model, or just make the call itself in the Controller. The example iOS project has some great patterns to follow.
Use AFHTTPClient. If you're interacting with a particular webservice, it can be very useful to have an AFHTTPClient subclass to handle all of those requests.
I am using the AWS SDK for iOS to upload and download files to and from local hard drive to Amazon S3 storage. I am capable of making this work but I am unable to get the S3 delegate to respond properly to alert me when operations have finished or resulted in an error.
I have an array of files that I want to upload. For each file I create a NSOperation where the main routine consist mostly of:
AmazonCredentials * credentials = [[AmazonCredentials alloc] initWithAccessKey:ACCESS_KEY_ID withSecretKey:SECRET_KEY];
putObjectRequest = [[S3PutObjectRequest alloc] initWithKey:pathCopy inBucket:[self bucket]];
putObjectRequest.filename = pathSource;
putObjectRequest.credentials=credentials;
[putObjectRequest setDelegate:s3Delegate];
Here, the delegate (s3Delegate) is created as a regular AmazonServiceRequestDelegate which should be able to fire off responses when an operation has finished. Each of my NSOperations are added to my NSOperationQueue which executes operations non-concurrently. If I use the delegate [putObjectRequest setDelegate:s3Delegate] the operations are not working. If I remove the use of the delegate the operations are performed correctly but I am unable to receive any responses to the operations as I do not have a delegate.
If I remove the use of the NSOperationQueue completely and use the [putObjectRequest setDelegate:s3Delegate] the delegate works perfectly.
My question is what am I doing wrong with using a delegate in a queue? Since the delegate is perfectly capable of performing while not in a queue could this be related to not performing on the main thread? I really want to be able to use the queue to limit the number of non-concurrent operations, however I am unable to figure this out. I hope someone has an idea of what is going on here and any example code would be greatly appreciated. Thanks!
Cheers, Trond
It seems that the aws sdk behaves asynchronously after the time you set your delegate.
So in order to have your asynchronous aws stuff work in a (asynchronous) NSOperation, you got to put some magic to wait for AWS to complete:
In your .h NSOperation file, add a boolean:
#interface UploadOperation : NSOperation <AmazonServiceRequestDelegate> {
#private
BOOL _doneUploadingToS3;
}
and in your .m file, your main method will look like this:
- (void) main
{
.... do your stuff …..
_doneUploadingToS3 = NO;
S3PutObjectRequest *por = nil;
AmazonS3Client *s3Client = [[AmazonS3Client alloc] initWithAccessKey:ACCESS_KEY withSecretKey:SECRET_KEY];
s3Client.endpoint = endpoint;
#try {
por = [[[S3PutObjectRequest alloc] initWithKey:KEY inBucket:BUCKET] autorelease];
por.delegate = self;
por.contentType = #"image/jpeg";
por.data = _imageData;
[s3Client putObject:por];
}
#catch (AmazonClientException *exception) {
_doneUploadingToS3 = YES;
}
do {
[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
} while (!_doneUploadingToS3);
por.delegate = nil;
.... continue with your stuff ….
}
do not forget to implement your delegate methods
-(void)request:(AmazonServiceRequest *)request didCompleteWithResponse:(AmazonServiceResponse *)response
{
_doneUploadingToS3 = YES;
}
-(void)request:(AmazonServiceRequest *)request didFailWithError:(NSError *)error
{
_doneUploadingToS3 = YES;
}
-(void)request:(AmazonServiceRequest *)request didFailWithServiceException:(NSException *)exception
{
_doneUploadingToS3 = YES;
}
- (void) request:(AmazonServiceRequest *)request didSendData:(NSInteger)bytesWritten totalBytesWritten:(NSInteger)totalBytesWritten totalBytesExpectedToWrite:(NSInteger)totalBytesExpectedToWrite
{
// Do what you want
}
-(void)request:(AmazonServiceRequest *)request didReceiveResponse:(NSURLResponse *)response
{
// Do what you want
}
-(void)request:(AmazonServiceRequest *)request didReceiveData:(NSData *)data
{
// Do what you want
}
Note: this magic can work for any stuff that performs asynchronously but have to be implemented in a NSOperation.
I have hit the proverbial wall trying to figure out how to populate an NSImage with data returned from an asynchronous NSURLConnection in my desktop app (NOT an iPhone application!!).
Here is the situation.
I have a table that is using custom cells. In each custom cell is an NSImage which is being pulled from a web server. In order to populate the image I can do a synchronous request easily:
myThumbnail = [[NSImage alloc] initWithContentsOfFile:myFilePath];
The problem with this is that the table blocks until the images are populated (obviously because it's a synchronous request). On a big table this makes scrolling unbearable, but even just populating the images on the first run can be tedious if they are of any significant size.
So I create an asynchronous request class that will retrieve the data in its own thread as per Apple's documentation. No problem there. I can see the data being pulled and populated (via my log files).
The problem I have is once I have the data, I need a callback into my calling class (the custom table view).
I was under the impression that I could do something like this, but it doesn't work because (I'm assuming) that what my calling class really needs is a delegate:
NSImage * myIMage;
myImage = [myConnectionClass getMyImageMethod];
In my connection class delegate I can see I get the data, I just don't see how to pass it back to the calling class. My connectionDidFinishLoading method is straight from the Apple docs:
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
// do something with the data
// receivedData is declared as a method instance elsewhere
NSLog(#"Succeeded! Received %d bytes of data",[receivedData length]);
// release the connection, and the data object
[connection release];
[receivedData release];
}
I am hoping this is a simple problem to solve, but I fear I am at the limit of my knowledge on this one and despite some serious Google searches and trying many different recommended approaches I am struggling to come up with a solution.
Eventually I will have a sophisticated caching mechanism for my app in which the table view checks the local machine for the images before going out and getting them form the server and maybe has a progress indicator until the images are retrieved. Right now even local image population can be sluggish if the image's are large enough using a synchronous process.
Any and all help would be very much appreciated.
Solution Update
In case anyone else needs a similar solution thanks to Ben's help here is what I came up with (generically modified for posting of course). Bear in mind that I have also implemented a custom caching of images and have made my image loading class generic enough to be used by various places in my app for calling images.
In my calling method, which in my case was a custom cell within a table...
ImageLoaderClass * myLoader = [[[ImageLoaderClass alloc] init] autorelease];
[myLoader fetchImageWithURL:#"/my/thumbnail/path/with/filename.png"
forMethod:#"myUniqueRef"
withId:1234
saveToCache:YES
cachePath:#"/path/to/my/custom/cache"];
This creates an instance of myLoader class and passes it 4 parameters. The URL of the image I want to get, a unique reference that I use to determine which class made the call when setting up the notification observers, the ID of the image, whether I want to save the image to cache or not and the path to the cache.
My ImageLoaderClass defines the method called above where I set what is passed from the calling cell:
-(void)fetchImageWithURL:(NSString *)imageURL
forMethod:(NSString *)methodPassed
withId:(int)imageIdPassed
saveToCache:(BOOL)shouldISaveThis
cachePath:(NSString *)cachePathToUse
{
NSURLRequest *theRequest=[NSURLRequest requestWithURL:[NSURL URLWithString:imageURL]
cachePolicy:NSURLRequestUseProtocolCachePolicy
timeoutInterval:60.0];
// Create the connection with the request and start loading the data
NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
if (theConnection) {
// Create the NSMutableData that will hold
// the received data
// receivedData is declared as a method instance elsewhere
receivedData = [[NSMutableData data] retain];
// Now set the variables from the calling class
[self setCallingMethod:methodPassed];
[self setImageId:imageIdPassed];
[self setSaveImage:shouldISaveThis];
[self setImageCachePath:cachePathToUse];
} else {
// Do something to tell the user the image could not be downloaded
}
}
In the connectionDidFinishLoading method I saved the file to cache if needed and made a notification call to any listening observers:
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
NSLog(#"Succeeded! Received %d bytes of data",[receivedData length]);
// Create an image representation to use if not saving to cache
// And create a dictionary to send with the notification
NSImage * mImage = [[NSImage alloc ] initWithData:receivedData];
NSMutableDictionary * mDict = [[NSMutableDictionary alloc] init];
// Add the ID into the dictionary so we can reference it if needed
[mDict setObject:[NSNumber numberWithInteger:imageId] forKey:#"imageId"];
if (saveImage)
{
// We just need to add the image to the dictionary and return it
// because we aren't saving it to the custom cache
// Put the mutable data into NSData so we can write it out
NSData * dataToSave = [[NSData alloc] initWithData:receivedData];
if (![dataToSave writeToFile:imageCachePath atomically:NO])
NSLog(#"An error occured writing out the file");
}
else
{
// Save the image to the custom cache
[mDict setObject:mImage forKey:#"image"];
}
// Now send the notification with the dictionary
NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
[nc postNotificationName:callingMethod object:self userInfo:mDict];
// And do some memory management cleanup
[mImage release];
[mDict release];
[connection release];
[receivedData release];
}
Finally in the table controller set up an observer to listen for the notification and send it off to the method to handle re-displaying the custom cell:
-(id)init
{
[super init];
NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
[nc addObserver:self selector:#selector(updateCellData:) name:#"myUniqueRef" object:nil];
return self;
}
Problem solved!
My solution is to use Grand Central Dispatch (GCD) for this purpose, you could save the image to disc too in the line after you got it from the server.
- (NSView *)tableView:(NSTableView *)_tableView viewForTableColumn:(NSTableColumn *)tableColumn row:(NSInteger)row
{
SomeItem *item = [self.items objectAtIndex:row];
NSTableCellView *cell = [_tableView makeViewWithIdentifier:tableColumn.identifier owner:self];
if (item.artworkUrl)
{
cell.imageView.image = nil;
dispatch_async(dispatch_queue_create("getAsynchronIconsGDQueue", NULL),
^{
NSURL *url = [NSURL URLWithString:item.artworkUrl];
NSImage *image = [[NSImage alloc] initWithContentsOfURL:url];
cell.imageView.image = image;
});
}
else
{
cell.imageView.image = nil;
}
return cell;
}
(I am using Automatic Reference Counting (ARC) therefore there are no retain and release.)
Your intuition is correct; you want to have a callback from the object which is the NSURLConnection’s delegate to the controller which manages the table view, which would update your data source and then call -setNeedsDisplayInRect: with the rect of the row to which the image corresponds.
Have you tried using the initWithContentsOfURL: method?