i´m using UIGraphicsBeginPDFContextToData to create PDF Files with Multiple Pages. Everything is working fine... My problem is that when the App creates a bigger amount of pages, for 1 PDF, its freezing for a short time and i have no control over the UI. The PDF File is created correctly, but i want to show a loading screen or something like that. Everything i tested like a UIAlertView within an UIActivityIndicator or just an UIActivityIndicator in the Toolbar are showing AFTER the PDF is done.
Here my method for creating the NSData Object. The NSLog shows the correct output:
I really have no idea how to show the progress of creating the PDF. A simple UILabel which shows the current page would be just what i need.
- (NSData *)createPDFData:(int)type {
NSLog(#"START");
NSMutableData *pdfData = [NSMutableData data];
UIGraphicsBeginPDFContextToData(pdfData, drawImage.bounds, nil);
if (type == 1) {
UIGraphicsBeginPDFPage();
if ([self loadPDFBackground]) [paperImage drawRect:paperImage.bounds];
[drawImage drawRect:drawImage.bounds];
} else if (type == 2) {
NSArray *images = [NSArray arrayWithArray:[self loadImagesForPDF]];
int imageCount = [images count];
for (int i=0; i<imageCount; i++) {
NSLog(#"%#", [NSString stringWithFormat:#"Page %i of %i", i+1, imageCount]);
drawImage.image = [images objectAtIndex:i];
UIGraphicsBeginPDFPage();
if ([self loadPDFBackground]) [paperImage drawRect:paperImage.bounds];
[drawImage drawRect:drawImage.bounds];
}
}
UIGraphicsEndPDFContext();
NSLog(#"END");
return pdfData;
}
I assume you are creating the PDF file on the main/UI thread and causes the application to freeze if the PDF file is very large. Since you are blocking the UI thread, no activity indicators can run and display progress. The solution is to run the PDF creation method on a separate thread and when the job is done, send a notification to the UI. In this way you can have the activity indicators and you dismiss them when you receive the notification from the PDF creation thread.
Related
I would like to create a pdfReader with a collectionview. What I want is to have a collectionview with Thumbnails of the pdf to display. So I use this in the viewDidLoad (to avoid the fact that it will generate the thumbnail in the collectionview each time we go down or up). It is generated one time, and it is without lag :
Loading the thumbnail of the pdf in viewDidLoad:
- (void)viewDidLoad
...
coverPdf = [NSMutableArray new];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^(void) {
// Load image on a non-ui-blocking thread
NSString *pdfPath = nil;
NSURL *pdfUrl = nil;
CGPDFDocumentRef pdfRef = nil;
NSMutableArray *arr = [NSMutableArray new];
for (id cover in filePathsArray)
{
pdfPath = [categoryPath stringByAppendingPathComponent:cover];
pdfUrl = [NSURL fileURLWithPath:pdfPath];
pdfRef = CGPDFDocumentCreateWithURL((CFURLRef)pdfUrl);
[arr addObject:[self imageFromPDFWithDocumentRef:pdfRef]];
NSLog(#"first process");
}
coverPdf = [NSMutableArray arrayWithArray:arr];
dispatch_sync(dispatch_get_main_queue(), ^(void) {
[pdfCollectionView reloadData];
});
});
...
}
Generating the thumbnail:
- (UIImage *)imageFromPDFWithDocumentRef:(CGPDFDocumentRef)documentRef
{
CGPDFPageRef pageRef = CGPDFDocumentGetPage(documentRef, 1);
CGRect pageRect = CGPDFPageGetBoxRect(pageRef, kCGPDFCropBox);
UIGraphicsBeginImageContext(pageRect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, CGRectGetMinX(pageRect),CGRectGetMaxY(pageRect));
CGContextScaleCTM(context, 1, -1);
CGContextTranslateCTM(context, -(pageRect.origin.x), -(pageRect.origin.y));
CGContextDrawPDFPage(context, pageRef);
UIImage *finalImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return finalImage;
}
Using the thumbnail:
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
ListPdfCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"CollectionViewCell" forIndexPath:indexPath];
cell.productLabel.text = [filePathsArray objectAtIndex:indexPath.row];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^(void) {
// Load image on a non-ui-blocking thread
dispatch_sync(dispatch_get_main_queue(), ^(void) {
// Assign image back on the main thread
if ([coverPdf count] > indexPath.row)
{
cell.pdfImage.image = [coverPdf objectAtIndex:indexPath.row];
}
});
});
return cell;
}
I have two problems with that method :
- The first one is that the thumbnail is taking too much time to appear. When it is loaded, it works well.
- The second problem, is that the memory is continually increasing and even if I close the viewcontroller, and I come in it, it seems that the memory is not released. If I close the viewcontroller and come in 9 or 10 times, if crash the app.
In conclusion, how can I create a collection view by loading the thumbnails of the pdfs in advance and how to avoid a crash with the memory increasing ?
Thanks in advance.
SOLUTION :
For the fact that it takes too much time to appear, I just replaced the DISPATCH_QUEUE_PRIORITY_BACKGROUND with the DISPATCH_QUEUE_PRIORITY_HIGH. It is much better.
For the memory leak, I used the CGPDFDocumentRelease() function just at the end of the loop like this, and all works like a charm :
for (id cover in filePathsArray)
{
pdfPath = [categoryPath stringByAppendingPathComponent:cover];
pdfUrl = [NSURL fileURLWithPath:pdfPath];
pdfRef = CGPDFDocumentCreateWithURL((CFURLRef)pdfUrl);
[arr addObject:[self imageFromPDFWithDocumentRef:pdfRef]];
CGPDFDocumentRelease(pdfRef);//Line added
NSLog(#"first process");
}
I have bad news for you. Memory leak is not your problem but iOS 10 memory management bug
There is a memory management bug in iOS 10.0.1 and 10.0.2 in the CGContextDrawPDFPage() function.
You can find details here http://www.openradar.me/28415289
Also you can find useful this discussion https://github.com/vfr/Reader/issues/166
In few words possible workaround is not to create
CGPDFPageRef pageRef = CGPDFDocumentGetPage(documentRef, 1);
each time but use one CGPDFPageRef for all of your pdf files. Then set it NULL when you not needs it anymore.
Creating thumbnails lag
And in terms of solution for creating thumbnails. I can only suggest not to do it in this VC at all but create thumbnail for each .pdf in the app at the moment when this .pdf added to the app (or on app launch in background service if all pdfs stored in the app bundle). Then you can save this previews as .jpg or .png files with names equal to pdf names or set relationships between pdf and preview in any database or other storage if you have it in your app.
Then just reuse this previews in your collectionView.
I'm having a problem where I'm unable to update UI when performing synchronous downloads. I would expect that using synchronous APIs would ensure that code executes in order (which it doesn't seem to be doing), which is really confusing me.
The following code is in a UICollectionView's didSelectItemAtIndexPath and is not wrapped in any asynchronous block or anything.
Any ideas on what I can do to be able to update the UI (most importantly a progress indicator) as these tasks occur? I think that the way it is currently laid out should work, but for some reason it's not able to update until the code has all 'executed'.
if ([internetReachable isReachable]) {
//does not become visible until after
self.circleProgress.alpha = 1.0;
//lots of downloading and saving with NSData dataWithContentsOfURL followed by this:
for (int i = 1; i < pages.count; i++) {
NSString *number;
if (i < 10) {
number = [NSString stringWithFormat:#"00%d", i];
}
else if (i < 100) {
number = [NSString stringWithFormat:#"0%d", i];
}
else {
number = [NSString stringWithFormat:#"%d", i];
}
NSURL *imageURL = [NSURL URLWithString:[NSString stringWithFormat:#"http://books.hardbound.co/%#/%#-%#.png", slug, slug, number]];
NSData *imageData = [NSData dataWithContentsOfURL:imageURL];
[df setObject:imageData forKey:[NSString stringWithFormat:#"%#-%#", slug, number]];
CGFloat progress = ((CGFloat)i / pages.count);
//only runs for the last iteration, rather than calling the method to update the progress indicator each iteration and allowing it to update before going back to the next iteration as I would expect
[self updateProgressBarWithAmount:[NSNumber numberWithFloat:progress]];
NSLog(#"progress after: %f", self.circleProgress.progress);
}
}
UI can only be executed on the main thread. Since the main thread is busy doing the downloading, it can't update the UI. It's almost never a good idea to perform any long running operations on the main thread. You should make the download asynchronous, and update the UI on the main thread.
The loop in the code you posted will only be executed after lots of downloading and saving with NSData dataWithContentsOfURL is performed, all the while the application will be unresponsive, and that's very poor UX. Take a look at this question for a much better implementation of a progress bar.
I am not by any means qualified to explain what exactly happens during each render loop and why updateProgress doesn't actually let a screen render occur before you block the main thread again, but I am able to provide a solution.
After you update the progress of the progress view, you want the changes to get rendered "right now". This means you have to tell the current run loop to run one iteration, and then return to you so you can do another long running task.
[[NSRunLoop currentRunLoop] runMode: NSDefaultRunLoopMode beforeDate: [NSDate date]];
Call that whoever you want the progress view to update, and it will do a screen render and then return to you.
I got this from this answer
However, you really should be doing this asynchronously.
(Apologies for any typos, as this is being typed on my phone)
Importing multiple photos from album, one of the delegate method is
// Here info is array of dictionary containing FileName/AssetURL etc
- (void)somePicker(SomePicker*)somePicker didFinishPickingMediaWithInfo:(NSArray *)info {
_importStatusView.center = self.view.center;
[self.view addSubview:_importStatusView];
[self dismissViewControllerAnimated:YES completion:^{
NSNumber *total = [NSNumber numberWithInteger:info.count];
[info enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
NSDictionary *imageInfo = (NSDictionary*)obj;
NSString *fileName = [imageInfo objectForKey:#"UIImagePickerControllerFileName"];
NSURL *imageURL = [imageInfo objectForKey:UIImagePickerControllerReferenceURL];
ALAssetsLibrary *assetLibrary=[[ALAssetsLibrary alloc] init];
[assetLibrary assetForURL:imageURL resultBlock:^(ALAsset *asset) {
NSLog(#"start");
ALAssetRepresentation *rep = [asset defaultRepresentation];
Byte *buffer = (Byte*)malloc(rep.size);
NSUInteger buffered = [rep getBytes:buffer fromOffset:0.0 length:rep.size error:nil];
NSData *data = [NSData dataWithBytesNoCopy:buffer length:buffered freeWhenDone:YES];
NSString *filePath = [_currentPath stringByAppendingPathComponent:fileName];
[data writeToFile:filePath atomically:YES];
//This also has no effect
//dispatch_async(dispatch_get_main_queue(), ^{
//_lblImportCountStatus.text = [NSString stringWithFormat:#"%d of %d",idx+1,[total integerValue]];
//NSLog(#"Label value->%#",_lblImportCountStatus.text); //This prints values but after everything is finished it prints all line at once i.e. at the end of the enumeration of all items
//});
//Update UI
NSNumber *current = [NSNumber numberWithInteger:idx+1];
NSDictionary *status = [NSDictionary dictionaryWithObjectsAndKeys:current,#"current", total,#"totalCount", nil];
[self performSelectorOnMainThread:#selector(updateImportCount:) withObject:status waitUntilDone:YES];
//_lblImportCountStatus.text = [NSString stringWithFormat:#"%d of %d",idx+1,[total integerValue]];
if(idx==info.count-1){
[_importStatusView removeFromSuperview];
}
NSLog(#"Finish");
} failureBlock:^(NSError *error) {
NSLog(#"Error: %#",[error localizedDescription]);
}];
}];
}];
}
My declaration for status view and label is
#property (strong, nonatomic) IBOutlet UIView *importStatusView; //View containing label
#property (weak, nonatomic) IBOutlet UILabel *lblImportCountStatus; //Label
Everything in above code is working fine and as expected, but the problem is a importStatusView is being added to the screen but lblImportCountStatus value is not displaying, though If I log the values it shows updated.
When enumeration is finished at the end all the NSLog gets printed for e.g. If I have imported 10 photos than at last it prints, i.e. dispatch_async(dispatch_get_main_queue() this function has no effect at all while enumeration is in progress.
Label value->1 of 10
Label value->2 of 10
Label value->3 of 10
Label value->4 of 10
Label value->5 of 10
Label value->6 of 10
Label value->7 of 10
Label value->8 of 10
Label value->9 of 10
Label value->10 of 10
What could be the issue ?
Update:
-(void)updateImportCount:(NSDictionary*)info{ //(NSNumber*)current forTotalItems:(NSNumber*)totalCount{
NSNumber *current = [info objectForKey:#"current"];
NSNumber *totalCount = [info objectForKey:#"totalCount"];
_lblImportCountStatus.text = [NSString stringWithFormat:#"%d of %d",[current integerValue],[totalCount integerValue]];
[_lblImportCountStatus setNeedsDisplay];
NSLog(#"Updating ui->%#",_lblImportCountStatus.text);
}
Above function works on main thread and updates but stil label is not shown it prints following NSLog
start
Updating ui->1 of 10
Finish
start
Updating ui->2 of 10
Finish
start
Updating ui->3 of 10
Finish
start
Updating ui->4 of 10
Finish
start
Updating ui->5 of 10
Finish
start
Updating ui->6 of 10
Finish
start
Updating ui->7 of 10
Finish
start
Updating ui->8 of 10
Finish
start
Updating ui->9 of 10
Finish
start
Updating ui->10 of 10
Finish
I have uploaded project at this location, please feel free to help.
All those blocks are executing on the main thread (the easiest way to verify this is using NSThread's +currentThread to get the current thread, and -isMainThread to check if it's the main thread. Anywhere you have code that you want to see what thread it's on, do something like this:
NSLog( #"enumeration block on main thread: %#",
[[NSThread currentThread] isMainThread] ? #"YES" : #"NO" );
I think the problem is, since this is all executing on the main thread, you're locking up the runloop, not giving the UI a chance to update.
The right way to fix this is probably to really do this processing on a separate thread (calling the code to update the UI via performSelectorOnMainThread:, as you're doing now). But, a quick hack to make it work would be to allow the runloop to run. At the end of updateImportCount:, do something like this:
[[NSRunLoop currentRunLoop] runUntilDate:[NSDate date]];
It ain't pretty, but it will work.
Update:
In Cocoa (Mac OS and iOS) there a concept of a runloop. The main thread of your application drives an NSRunLoop which serves as the event loop. User actions -- taps, etc. -- are processed through this loop, as are things like timers, network connections, and other things. See the NSRunLoop Reference for more information on that.
In iOS, drawing also happens on the runloop. So when you call setNeedsDisplay on a view, that view is not redrawn immediately. Rather, it's simply flagged as needing redraw, and then on the next drawing cycle (the next trip through the runloop) the actual drawing takes place. The UIView reference has a brief description of this (see the section "The View Drawing Cycle". Quoting from that section:
When the actual content of your view changes, it is your
responsibility to notify the system that your view needs to be
redrawn. You do this by calling your view’s setNeedsDisplay or
setNeedsDisplayInRect: method of the view. These methods let the
system know that it should update the view during the next drawing
cycle. Because it waits until the next drawing cycle to update the
view, you can call these methods on multiple views to update them at
the same time.
When you return from whatever method was called in response to some user action (in this case, somePicker:didFinishPickingMediaWithInfo:, control returns to the runloop, and any views that need redrawing, are. However, if you do a bunch of processing on the main thread without returning, the runloop is basically stalled, and drawing won't take place. The code above basically gives the runloop some time to process, so drawing can take place. [NSDate date] returns the current date and time, right now, so that basically tells the runlooop "run until right now", which ends up giving it one cycle through the loop, giving you one drawing cycle, which is an opportunity for your label to be redrawn.
I have a simple iPhone app that is parsing data (titles, images etc.) from rss feed and showing in the tableview.
The viewDidLoad has an initial counter value to reach the first page of the feed and load in the tableview by calling the fetchEntriesNew method:
- (void)viewDidLoad
{
[super viewDidLoad];
counter = 1;
[self fetchEntriesNew:counter];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(dataSaved:)
name:#"DataSaved" object:nil];
}
- (void) fetchEntriesNew:(NSInteger )pageNumber
{
channel = [[TheFeedStore sharedStore] fetchWebService:pageNumber withCompletion:^(RSSChannel *obj, NSError *err){
if (!err) {
int currentItemCount = [[channel items] count];
channel = obj;
int newItemCount = [[channel items] count];
NSLog(#"Total Number Of Entries Are: %d", newItemCount);
counter = (newItemCount / 10) + 1;
NSLog(#"New Counter Should Be %d", counter);
int itemDelta = newItemCount - currentItemCount;
if (itemDelta > 0) {
NSMutableArray *rows = [NSMutableArray array];
for (int i = 0; i < itemDelta; i++) {
NSIndexPath *ip = [NSIndexPath indexPathForRow:i inSection:0];
[rows addObject:ip];
}
[[self tableView] insertRowsAtIndexPaths:rows withRowAnimation:UITableViewRowAnimationBottom];
[aiView stopAnimating];
}
}
}];
[[self tableView] reloadData];
}
When the user reaches the bottom of the tableview, i am using the following to reach the next page of the feed and load at the bottom of the first page that was loaded first:
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
float endScrolling = scrollView.contentOffset.y + scrollView.frame.size.height;
if (endScrolling >= scrollView.contentSize.height)
{
NSLog(#"Scroll End Called");
NSLog(#"New Counter NOW is %d", counter);
[self fetchEntriesNew:counter];
}
}
UPDATE2: Here is a more easy to understand description of whats wrong that i am unable to solve: For example there are 10 entries in the each page of the rss feed. The app starts, titles and other labels are loaded immediately and images starts loading lazily and finally gets finished. So far so good. The user scrolls to reach the bottom, reaching the bottom will use the scroll delegate method and the counter gets incremented from 1 to 2 telling the fetchEntriesNew method to reach the second page of the rss feed. The program will start loading the next 10 entries at the bottom of first 10 previously fetched. This can go on and the program will fetch 10 more entries every time the user scrolls and reaches bottom and the new rows will be placed below the previously fetched ones. So far so good.
Now let us say the user is on page 3 currently which has been loaded completely with the images. Since page 3 is loaded completely that means currently there are 30 entries in the tableview. The user now scrolls to the bottom, the counter gets incremented and the tableview begins populating the new rows from page 4 of the rss feed at the bottom of the first 30 entries. Titles get populated quickly thus building the rows and while the images are getting downloaded (not downloaded completely yet), the user quickly moves to the bottom again, instead of loading the 5th page at the bottom of the 4th, it will destroy the 4th ones that is currently in the middle of getting downloaded and starts loading the 4th one again.
What it should do is that it should keep on titles etc from next pages when user reaches the bottom of the tableview regardless of whether the images of the previous pages are in the middle of getting downloaded or not.
There is NO issue with the downloading and persisting data in my project and all the data is persisted between the application runs.
Can someone help to point me out to the right direction. Thanks in advance.
UPDATE 3: Based on #Sergio's answer, this is what i did:
1) Added another call to archiveRootObject [NSKeyedArchiver archiveRootObject:channelCopy toFile:cachePath]; after [channelCopy addItemsFromChannel:obj];
At this point, its not destroying and reloading the same batch again and again, exactly what i wanted. However, it doesn't persist images if i scroll multiple times to reach the next page without the images of the previous page were loaded completely.
2) I am not sure how to use Bool as he explained in the answer. This is what i did: Added #property Bool myBool; in TheFeedStore, synthesised it and set it to NO after newly added archiveRootObject:channelCopy and set it to YES in ListViewController at the very start of fetchEntries method. It didn't work.
3) I also realised the way i am dealing with the whole issue is performance vice not better. Although i don't know how to use images outside the cache and handle them as sort of cache. Are you suggesting to use a separate archiving file for images?
Thanks a lot to all people who have contributed in trying to solve my issue.
Your issue can be understood if you consider this older question of yours and the solution I proposed.
Specifically, the critical bit has to do with the way you are persisting the information (RSS info + images), which is through archiving your whole channel to a file on disk:
[channelCopy addItemsFromChannel:obj];
[NSKeyedArchiver archiveRootObject:channelCopy toFile:pathOfCache];
Now, if you look at fetchEntriesNew:, the first thing that you do there is destroying your current channel. If this happens before the channel has been persisted to disk you enter a sort of endless loop.
I understand you are currently persisting your channel (as per my original suggestion) at the very end of image download.
What you should do is persisting the channel just after the feed has been read and before starting downloading the images (you should of course also persist it at the end of image downloads).
So, if you take this snippet from my old gist:
[connection setCompletionBlock:^(RSSChannel *obj, NSError *err) {
if (!err) {
[channelCopy addItemsFromChannel:obj];
// ADDED
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
dispatch_group_wait(obj.imageDownloadGroup, DISPATCH_TIME_FOREVER);
[NSKeyedArchiver archiveRootObject:channelCopy toFile:cachePath];
});
}
block(channelCopy, err);
what you should do is adding one more archiveRootObject call:
[connection setCompletionBlock:^(RSSChannel *obj, NSError *err) {
if (!err) {
[channelCopy addItemsFromChannel:obj];
[NSKeyedArchiver archiveRootObject:channelCopy toFile:cachePath];
// ADDED
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
dispatch_group_wait(obj.imageDownloadGroup, DISPATCH_TIME_FOREVER);
[NSKeyedArchiver archiveRootObject:channelCopy toFile:cachePath];
});
}
block(channelCopy, err);
This will make things work as long as you do not scroll fast enough so that the channel is destroyed before the feed (without images) is ever read. To fix this you should add a bool to your TheFeedStore class that you set to YES when you call fetchWebService and reset just after executing the newly added archiveRootObject:channelCopy.
This will fix your issues.
Let me also say that from a design/architecture point of view, you have a big issue with the way you manage persistence. Indeed, you have a single file on disk that you write atomically using archiveRootObject. This architecture is intrinsically "risky" from a multi-threading point of view and you should also devise a way to avoid that concurrent accesses to the shared stored have no destructive effects (e.g.: you archive your channel to disk for page 4 at the same time as the images for page 1 have been fully downloaded, hence you try to persist them as well to the same file).
Another approach to image handling would be storing the images outside of your archive file and treat them as a sort of cache. This would fix the concurrency issues and will also get rid of the performance penalty you get from archiving the channel twice for each page (when the feed is first read and later when the images have come in).
Hope this helps.
UPDATE:
At this point, its not destroying and reloading the same batch again and again, exactly what i wanted. However, it doesn't persist images if i scroll multiple times to reach the next page without the images of the previous page were loaded completely.
This is exactly what I meant saying that your architecture (shared archive/concurrent access) would probably lead to problems.
You have several options: use Core Data/sqlite; or, more easily, store each image in its own file. In the latter case, you could do following:
on retrieval, assign to each image a filename (this could be the id of the feed entry or a sequential number or whatever) and store the image data there;
store in the archive both the URL of the image and the filename where it should be stored;
when you need accessing the image, you don't get it from the archived dictionary directly; instead, you get the filename from the it then read the file from disk (if available);
this change would not affect otherwise your current implementation of rss/image retrieval, but only the way you persist the images and you access them when required (I mean, it seems a pretty easy change).
2) I am not sure how to use Bool as he explained in the answer.
add a isDownloading bool to TheFeedStore;
set it to YES in your fetchWebService: method, just before doing [connection start];
set it to NO in the completion block you pass to the connection object (again in fetchWebService:) right after archiving the feed the first time (this you are already doing);
in your scrollViewDidEndDecelerating:, at the very beginning, do:
if ([TheFeedStore sharedStore].isDownloading)
return;
so that you do not refresh the rss feed while a refresh is ongoing.
Let me know if this helps.
NEW UPDATE:
Let me sketch how you could deal with storing images in files.
In your RSSItem class, define:
#property (nonatomic, readonly) UIImage *thumbnail;
#property (nonatomic, strong) NSString *thumbFile;
thumbFile is the the path to the local file hosting the image. Once you have got the image URL (getFirstImageUrl), you can get, e.g., and MD5 hash of it and use this as your local image filename:
NSString* imageURLString = [self getFirstImageUrl:someString];
....
self.thumbFile = [imageURLString MD5String];
(MD5String is a category you can google for).
Then, in downloadThumbnails, you would store the image file locally:
NSMutableData *tempData = [NSData dataWithContentsOfURL:finalUrl];
[tempData writeToFile:[self cachedFileURLFromFileName:self.thumbFile] atomically:YES];
[[NSNotificationCenter defaultCenter] postNotificationName:#"DataSaved" object:nil];
Now, the trick is, when you access the thumbnail property, you read the image from file and return it:
- (UIImage *)thumbnail
{
NSData* d = [NSData dataWithContentsOfURL:[self cachedFileURLFromFileName:self.thumbFile]];
return [[UIImage alloc] initWithData:d];
}
in this snippet, cachedFileURLFromFileName: is defined as:
- (NSURL*)cachedFileURLFromFileName:(NSString*)filename {
NSFileManager *fileManager = [[NSFileManager alloc] init];
NSArray *fileArray = [fileManager URLsForDirectory:NSCachesDirectory inDomains:NSUserDomainMask];
NSURL* cacheURL = (NSURL*)[fileArray lastObject];
if(cacheURL)
{
return [cacheURL URLByAppendingPathComponent:filename];
}
return nil;
}
Of course, thumbFile should be persisted for this to work.
As you see, this approach is pretty "easy" to implement. This is not an optimized solution, just a quick way to make your app work with its current architecture.
For completeness, the MD5String category:
#interface NSString (MD5)
- (NSString *)MD5String;
#end
#implementation NSString (MD5)
- (NSString *)MD5String {
const char *cstr = [self UTF8String];
unsigned char result[16];
CC_MD5(cstr, strlen(cstr), result);
return [NSString stringWithFormat:
#"%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X",
result[0], result[1], result[2], result[3],
result[4], result[5], result[6], result[7],
result[8], result[9], result[10], result[11],
result[12], result[13], result[14], result[15]
];
}
#end
What you are actually trying to do, is implement paging in a UITableView
Now this is very straightforward and the best idea is to implement the paging in your UITableView delegate cellForRowAtIndexPath method, instead of doing this on the UIScrollView scrollViewDidEndDecelerating delegate method.
Here is my implementation of paging and I believe it should work perfectly for you too:
First of all, I have an implementation constants related to the paging:
//paging step size (how many items we get each time)
#define kPageStep 30
//auto paging offset (this means when we reach offset autopaging kicks in, i.e. 10 items before the end of list)
#define kPageBegin 10
The reason I'm doing this is to easily change the paging parameters on my .m file.
Here is how I do paging:
- (UITableViewCell*)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
NSUInteger row = [indexPath row];
int section = indexPath.section-1;
while (section>=0) {
row+= [self.tableView numberOfRowsInSection:section];
section--;
}
if (row+kPageBegin>=currentItems && !isLoadingNewItems && currentItems+1<maxItems) {
//begin request
[self LoadMoreItems];
}
......
}
currentItems is an integer that has the number of the tableView datasource current items.
isLoadingNewItems is a boolean that marks if items are being fetched at this moment, so we don't instantiate another request while we are loading the next batch from the server.
maxItems is an integer that indicates when to stop paging, and is an value that I retrieve from our server and set it on my initial request.
You can omit the maxItems check if you don't want to have a limit.
and in my paging loading code I set the isLoadingNewItems flag to true and set it back to false after I retrieve the data from the server.
So in your situation this would look like:
- (UITableViewCell*)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
NSUInteger row = [indexPath row];
int section = indexPath.section-1;
while (section>=0) {
row+= [self.tableView numberOfRowsInSection:section];
section--;
}
if (row+kPageBegin>=counter && !isDowloading) {
//begin request
isDowloading = YES;
[self fetchEntriesNew:counter];
}
......
}
Also there is no need to reload your whole table after adding the new rows.
Just use this:
for (int i = 0; i < itemDelta; i++) {
NSIndexPath *ip = [NSIndexPath indexPathForRow:i inSection:0];
[rows addObject:ip];
}
[self.tableView beginUpdates];
[self.tableView insertRowsAtIndexPaths:rows withRowAnimation:UITableViewRowAnimationBottom];
[self.tableView endUpdates];
A simple BOOL is enough to avoid repetitive calls:
BOOL isDowloading;
When the download is done, set it to NO. When it enters here:
if (endScrolling >= scrollView.contentSize.height)
{
NSLog(#"Scroll End Called");
NSLog(#"New Counter NOW is %d", counter);
[self fetchEntriesNew:counter];
}
put it to YES. Also don't forget to set it to NO when the requests fails.
Edit 1:
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
float endScrolling = scrollView.contentOffset.y + scrollView.frame.size.height;
if (endScrolling >= scrollView.contentSize.height)
{
if(!isDowloading)
{
isDownloading = YES;
NSLog(#"Scroll End Called");
NSLog(#"New Counter NOW is %d", counter);
[self fetchEntriesNew:counter];
}
}
}
And when you finish fetching, just set it to NO again.
Any idea why this crashes? What am I doing wrong?
Thanks!
-(IBAction)animationOneStart {
NSMutableArray* arrayOfImages = [[NSMutableArray alloc]initWithCapacity:10];
for(int count = 1; count <= 22; count++)
{
NSString *path = [NSString stringWithFormat:#"testDance3_%03d.jpg", count];
UIImage* img = [[UIImage alloc]initWithContentsOfFile:path];
[arrayOfImages addObject:img];
[img release];
}
loadingImageView.animationImages = arrayOfImages;
[arrayOfImages release];
loadingImageView.animationDuration = 3;
loadingImageView.animationRepeatCount = 1; //Repeats indefinitely
[loadingImageView startAnimating];
loadingImageView.animationImages = nil;
[loadingImageView release];
}
Try initializing your NSMutableDictionary with capacity for the same quantity of object's you'll be storing in it. If that doesn't work, I'd try to comment out these two lines:
//loadingImageView.animationImages = nil;
//[loadingImageView release];
In the scope of this code, your other calls appear balanced. But we can't see what's happening inside loadingImageView, and so my guess is that either the loadingImageView itself or it's animations are being released prematurely.
I can't see enough code confirm this, but a couple things that are suspicious are here:
[loadingImageView startAnimating];
loadingImageView.animationImages = nil;
[loadingImageView release];
So, while the animation is running, you are releasing the images that are being animated? Or the view which, itself, is animating? Probably one or the other or both is the problem.
If the animation is supposed to run indefinitely, you are going to need to keep the view around indefinitely. And if it stops eventually, you should release it after it stops.
You call to addObject will fail when nil is passed. The UIImage could be nil when your system run out of memory and cannot allocate more. When that happens depends on how large your images are, but basically you can be sure that sooner of later use of loadingImageView.animationImages combined with allocating all your UIImage objects at the same time will cause your app to crash. See also playing-looping-images-sequence-in-uiview. You basically need a different approach that does not hold all the images in memory at the same time, the uncompressed images consume way too much memory.