I download images and use it in my app. I have more then 100 images and I use it not all at a time. I will use cache. Then I load all images I save it to cache. Then I will go to the other parts of the app and I will use some that images.
I not really understand how the ios cache works and I have a question: after load all images and saving it to cache, how should I use this images, I mean, I need load them from cache or use instances of images that I have before saving it ti cache ?
And what caching strategy is more useful with AFNetworking 2.0?
AFNetworking has in-memory caching for images. If you have 100 images it could appropriate for you, could be not.
You should also read about NSURLCache here - http://nshipster.com/nsurlcache/.
If you use NSURLCache you do not have to think about caching - when you start downloading something that is already cached, system will just give you downloaded file.
UPDATE:
Time expiration for downloaded data is set by server in response. But you can edit or ignore it by NSURLConnectionDelegate method. Example:
- (NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse {
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)[cachedResponse response];
// Look up the cache policy used in our request
if([connection currentRequest].cachePolicy == NSURLRequestUseProtocolCachePolicy) {
NSDictionary *headers = [httpResponse allHeaderFields];
NSString *cacheControl = [headers valueForKey:#"Cache-Control"];
NSString *expires = [headers valueForKey:#"Expires"];
if((cacheControl == nil) && (expires == nil)) {
NSLog(#"server does not provide expiration information and we are using NSURLRequestUseProtocolCachePolicy");
return nil; // don't cache this
}
}
return cachedResponse;
}
Related
My app offers the option to download 3430 high resolution images from our server, each image of size 50k - 600k bytes.
The original approach was to just download all of them - but we realized that gave a lot of NSURLErrorTimedOut errors and crashed our program. We then implemented it such that we download all of the images, but in batches of 100 images at a time. Someone on SO suggested we actually implement our download like this:
Create a list of all file URLs that need to be downloaded.
Write your code so that it downloads these URLs sequentially. I.e. do
not let it start downloading a file until the previous one has
finished (or failed and you decided to skip it for now).
Use NSURLSession's support for downloading an individual file to a
folder, don't use the code to get an NSData and save the file
yourself. That way, your application doesn't need to be running while
the download finishes.
Ensure that you can tell whether a file has already been downloaded or
not, in case your download gets interrupted, or the phone is restarted
in mid-download. You can e.g. do this by comparing their names (if
they are unique enough), or saving a note to a plist that lets you
match a downloaded file to the URL where it came from, or whatever
constitutes an identifying characteristic in your case.
At startup, check whether all files are there. If not, put the missing
ones in above download list and download them sequentially, as in #2.
Before you start downloading anything (and that includes downloading
the next file after the previous download has finished or failed), do
a reachability check using the Reachability API from Apple's
SystemConfiguration.framework. That will tell you whether the user has
a connection at all, and whether you're on WiFi or cellular (in
general, you do not want to download a large number of files via
cellular, most cellular connections are metered).
We create a list of all images to download here:
- (void)generateImageURLList:(BOOL)batchDownloadImagesFromServer
{
NSError* error;
NSFetchRequest* leafletURLRequest = [[[NSFetchRequest alloc] init] autorelease];
NSEntityDescription* leafletURLDescription = [NSEntityDescription entityForName:#"LeafletURL" inManagedObjectContext:managedObjectContext];
[leafletURLRequest setEntity:leafletURLDescription];
numberOfImages = [managedObjectContext countForFetchRequest:leafletURLRequest error:&error];
NSPredicate* thumbnailPredicate = [NSPredicate predicateWithFormat:#"thumbnailLocation like %#", kLocationServer];
[leafletURLRequest setPredicate:thumbnailPredicate];
self.uncachedThumbnailArray = [managedObjectContext executeFetchRequest:leafletURLRequest error:&error];
NSPredicate* hiResPredicate = [NSPredicate predicateWithFormat:#"hiResImageLocation != %#", kLocationCache];
[leafletURLRequest setPredicate:hiResPredicate];
self.uncachedHiResImageArray = [managedObjectContext executeFetchRequest:leafletURLRequest error:&error];
}
We use NSURLSession to download an individual image to a folder by calling hitServerForUrl and implementing didFinishDownloadingToURL:
- (void)hitServerForUrl:(NSURL*)requestUrl {
NSURLSessionConfiguration *defaultConfigurationObject = [NSURLSessionConfiguration defaultSessionConfiguration];
NSURLSession *defaultSession = [NSURLSession sessionWithConfiguration:defaultConfigurationObject delegate:self delegateQueue: nil];
NSURLSessionDownloadTask *fileDownloadTask = [defaultSession downloadTaskWithURL:requestUrl];
[fileDownloadTask resume];
}
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location {
if (isThumbnail)
{
leafletURL.thumbnailLocation = kLocationCache;
}
else
{
leafletURL.hiResImageLocation = kLocationCache;
}
// Filename to write to
NSString* filePath = [leafletURL pathForImageAtLocation:kLocationCache isThumbnail:isThumbnail isRetina:NO];
// If it's a retina image, append the "#2x"
if (isRetina_) {
filePath = [filePath stringByReplacingOccurrencesOfString:#".jpg" withString:#"#2x.jpg"];
}
NSString* dir = [filePath stringByDeletingLastPathComponent];
[managedObjectContext save:nil];
NSError* error;
[[NSFileManager defaultManager] createDirectoryAtPath:dir withIntermediateDirectories:YES attributes:nil error:&error];
NSURL *documentURL = [NSURL fileURLWithPath:filePath];
NSLog(#"file path : %#", filePath);
if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
//Remove the old file from directory
}
[[NSFileManager defaultManager] moveItemAtURL:location
toURL:documentURL
error:&error];
if (error){
//Handle error here
}
}
This code calls loadImage, which calls `hitServer:
-(void)downloadImagesFromServer{
[self generateImageURLList:NO];
[leafletImageLoaderQueue removeAllObjects];
numberOfHiResImageLeft = [uncachedHiResImageArray count];
for ( LeafletURL* aLeafletURL in uncachedHiResImageArray)
{
//// Do the same thing again, except set isThumb = NO. ////
LeafletImageLoader* hiResImageLoader = [[LeafletImageLoader alloc] initWithDelegate:self];
[leafletImageLoaderQueue addObject:hiResImageLoader]; // do this before making connection!! //
[hiResImageLoader loadImage:aLeafletURL isThumbnail:NO isBatchDownload:YES];
//// Adding object to array already retains it, so it's safe to release it here. ////
[hiResImageLoader release];
uncachedHiResIndex++;
NSLog(#"uncached hi res index: %ld, un cached hi res image array size: %lu", (long)uncachedHiResIndex, (unsigned long)[uncachedHiResImageArray count]);
}
}
- (void)loadImage:(LeafletURL*)leafletURLInput isThumbnail:(BOOL)isThumbnailInput isBatchDownload:(BOOL)isBatchDownload isRetina:(BOOL)isRetina
{
isRetina_ = isRetina;
if (mConnection)
{
[mConnection cancel];
[mConnection release];
mConnection = nil;
}
if (mImageData)
{
[mImageData release];
mImageData = nil;
}
self.leafletURL = leafletURLInput;
self.isThumbnail = isThumbnailInput;
NSString* location = (self.isThumbnail) ?leafletURL.thumbnailLocation :leafletURL.hiResImageLocation;
//// Check if the image needs to be downloaded from server. If it is a batch download, then override the local resources////
if ( ([location isEqualToString:kLocationServer] || (isBatchDownload && [location isEqualToString:kLocationResource])) && self.leafletURL.rawURL != nil )
{
//NSLog(#"final loadimage called server");
//// tell the delegate to get ride of the old image while waiting. ////
if([delegate respondsToSelector:#selector(leafletImageLoaderWillBeginLoadingImage:)])
{
[delegate leafletImageLoaderWillBeginLoadingImage:self];
}
mImageData = [[NSMutableData alloc] init];
NSURL* url = [NSURL URLWithString:[leafletURL pathForImageOnServerUsingThumbnail:self.isThumbnail isRetina:isRetina]];
[self hitServerForUrl:url];
}
//// if not, tell the delegate that the image is already cached. ////
else
{
if([delegate respondsToSelector:#selector(leafletImageLoaderDidFinishLoadingImage:)])
{
[delegate leafletImageLoaderDidFinishLoadingImage:self];
}
}
}
Currently, I'm trying to figure out how to download the images sequentially, such that we don't call hitServer until the last image is finished downloading. Do I need to be downloading in the background? Thank you for suggestions!
My app offers the option to download 3430 high resolution images from our server, each image of size 50k - 600k bytes.
This seems like a job for on-demand resources. Just turn these files into on-demand resources obtained from your own server, and let the system take care of downloading them in its own sweet time.
This sounds very much like an architectural issue. If you fire off downloads without limiting them of course you're going to start getting timeouts and other things. Think about other apps and what they do. Apps that give the user the ability to do multiple downloads often limit how may can occur at once. iTunes for example can queue up thousands of downloads, but only runs 3 at a time. Limiting to just one at a time will only slow things down for your users. You need a balance that consider your user's available bandwidth.
The other part of this is to again consider what your users want. Does every one of your uses want every single image? I don't know what you are offering them, but in most apps which access resources like images or music, it's up to the user what and when they download. Thus they only download what they are interested in. So I'd recommend only downloading what the users are viewing or have somehow requested they want to download.
I am working on a browser application and i want to track how much internet data is consumed when a web page is load.
I am using this method to calculate data received by iOS application.
- (void)connectionDidFinishLoading:(NSURLConnection *)connection{
NSLog(#"Did Receive Data %i", [resourceData length]);
length += [resourceData length];
NSLog(#"Data in MB: %.3f",(length/(1024*1024)));
}
I am opening http://www.google.com in iOS simulator and same browser application for android.
When page load completes iOS application show 20KB data used but android application shows 280KB data used.
In android there is a class to get data used in an active session, that class name is TrafficStats. I search a lot but in iOS, i don't find any class or method that have similar.
I also try this code when webViewDidFinishLoading called to get actual data consumed by webView to load that page.
-(void)webViewDidFinishLoad:(UIWebView *)webView{
NSString* script = #"document.documentElement.outerHTML.length";
length += [[webBrowser stringByEvaluatingJavaScriptFromString:script] floatValue];
NSLog(#"Data in MB: %.3f",(length/(1024*1024)));
//[self performSelectorOnMainThread:#selector(dataUsedByApp) withObject:nil waitUntilDone:5.0];
}
But this is also not accurate because it doesn't calculate the size of images and size is calculated with #"document.documentElement.outerHTML.length".
Please help me on this. :)
Use dataWithContentsOfURL method:
NSData *resultData = [NSData dataWithContentsOfURL:#"https://www.google.co.in/logos/doodles/2014/world-cup-2014-57-5105522332139520.2-hp.gif"];
NSUInteger dataLength = resultData.length;
But here to get the URL for the image, you require to parse the entire HTML which is getting in response by https://www.google.co.in.
Hope this is what you are looking for.
Update:
Get html page size :
NSData *resultData = [NSData
dataWithContentsOfURL:#"https://www.google.co.in"];
Parse all the resource are there in the page. For that you require to do XML parsing of the entire data response. (by converting in to NSString) For that you might require to look into internet.
Once you get all the resource URLs like I got for logo.gif, get its NSData length individualy
At the end summation of all these is your solution:
PageSize + AllResourcesSize = Entire Page Load Size
You can intercept the requests with the opensource WebViewProxy (https://github.com/marcuswestin/WebViewProxy).
I can imagine that this will work if you want to track all http traffic, or you can change the predicate to fit your case:
[WebViewProxy handleRequestsMatching:[NSPredicate predicateWithFormat:#"absoluteString MATCHES[cd] '^http:'"] handler:^(NSURLRequest* req, WVPResponse *res) {
[NSURLConnection sendAsynchronousRequest:[NSURLRequest requestWithURL:req.URL] queue:queue completionHandler:^(NSURLResponse *netRes, NSData *data, NSError *netErr) {
//do your transfer logging here
....
[res respondWithData:data mimeType:netRes.MIMEType];
}];
}];
I'm quite new to Amazon S3 and I'm having difficulty downloading large files from S3.
I have successfully downloaded a file that is 35MB every time, but when the size of the file is really big around 500 MB - 1.7GB the application crashes.
When trying on the simulator I would get can't allocate region error after about 1GB of the download.
So then I tried it on the device. Now it seems to just crash at a random time and
no crash report is put in the device, therefor I'm having an issue debugging this problem.
At first I thought it was the device or even the simulator. But i'm not really sure.
Someone mentioned that S3 framework times out the downloads randomly occasionally for large files. Could this be the case?
I'm building the file by opening a data file seeking to the end, adding the data, then closing the file until the download is complete.
I'm not sure how to debug this problem.
Any help would be appreciated.
Thank you.
I am a maintainer of the AWS SDK for iOS. We recently patched the S3GetObjectResponse to allow the streaming of the data directly to disk without keeping the response data in memory.
S3GetObjectResponse.m
To enable this, you simply need to set the stream when creating your request:
NSOutputStream *outputStream = [[[NSOutputStream alloc] initToFileAtPath:FILE_NAME append:NO] autorelease];
[outputStream open];
S3GetObjectRequest *getObjectRequest = [[[S3GetObjectRequest alloc] initWithKey:FILE_NAME withBucket:BUCKET_NAME] autorelease];
getObjectRequest.outputStream = outputStream;
[s3 getObject:getObjectRequest];
Update: We added a post to our AWS Mobile Developer Blog on downloading large files with the AWS SDK for iOS that includes this info as well as other tips.
S3GetObjectRequest has NSMutableData* body where it appends all the data it downloads.
For large files as download progresses data is appended constantly, and it goes over the VM limit of 90MB and then app gets killed by iOS.
Quick and dirty workaround is to create your own S3GetObjectRequest and S3GetObjectResponse classes. AWS framework instantiates Response based on Class Name of Request (Class name of Request without last 7 chars "Request" and appends it with "Response", and tries to instantiate new class of that name).
Then to override -(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data to release body all the time.
This is quick and dirty fix simply because you still have constant data allocation, appending and then release. But it works when you are in a pinch. For my usage of downloading files of 150-700mb, this simple hack kept memory usage of the app at 2.55mb average, +/- 0.2mb.
As stated by the author of ASIHTTP library, it is no longer maintained.
Request - LargeFileS3GetObjectRequest.h
#interface LargeFileS3GetObjectRequest : S3GetObjectRequest
#end
Request - LargeFileS3GetObjectRequest.m
#implementation LargeFileS3GetObjectRequest
#end
Response - LargeFileS3GetObjectResponse.h
#interface LargeFileS3GetObjectResponse : S3GetObjectResponse
#end
Response - LargeFileS3GetObjectResponse.m
#implementation LargeFileS3GetObjectResponse
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
// allow original implementation to send data to delegates
[super connection:connection didReceiveData:data];
// release body and set it to NULL so that underlying implementation doesn't
// append on released object, but instead allocates new one
[body release];
body = NULL;
}
#end
Hope it helps.
You may want to stream the data to your application via ASIHTTPRequest
http://allseeing-i.com/ASIHTTPRequest/S3
NSString *secretAccessKey = #"my-secret-access-key";
NSString *accessKey = #"my-access-key";
NSString *bucket = #"my-bucket";
NSString *path = #"path/to/the/object";
ASIS3ObjectRequest *request = [ASIS3ObjectRequest requestWithBucket:bucket key:path];
[request setSecretAccessKey:secretAccessKey];
[request setAccessKey:accessKey];
[request startSynchronous];
if (![request error]) {
NSData *data = [request responseData];
} else {
NSLog(#"%#",[[request error] localizedDescription]);
}
/* Set up the Amazon client */
_s3 = [[AmazonS3Client alloc] initWithAccessKey:k_Amazon_ACCESS_KEY_ID withSecretKey:k_Amazon_SECRET_KEY];
_s3.endpoint = [AmazonEndpoints s3Endpoint:SA_EAST_1];
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(queue, ^{
/* Open a file stream for the download */
NSOutputStream *outputStream = [[NSOutputStream alloc] initToFileAtPath:[DOCUMENTS_DIRECTORY stringByAppendingPathComponent:k_Amazon_Video_Local_File_Name] append:NO];
[outputStream open];
/* Set up the s3 get object */
S3GetObjectRequest *getVideoRequest = [[S3GetObjectRequest alloc] initWithKey:k_Amazon_Video_Path withBucket:#""];
/* Set the stream */
getVideoRequest.outputStream = outputStream;
/* Get the response from Amazon */
S3GetObjectResponse *getObjectResponse = [_s3 getObject:getVideoRequest];
dispatch_async(dispatch_get_main_queue(), ^{
if(getObjectResponse.error != nil)
{
NSLog(#"S3 Error: %#", getObjectResponse.error);
}
else
{
NSLog(#"S3 - Video download complete and successful");
[[NSUserDefaults standardUserDefaults] setBool:YES forKey:k_Amazon_Video_Downloaded];
}
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
});
});
I understand the need of image compression while downloading images when connected to a 3G network, but I am getting really bad looking images... I'm caching downloaded images and I realized that the quality of the images depends on the active connection. My code:
KTMember *member = [[DataManager sharedManager] getMemberWithId:memberId];
if (member) {
NSLog(#"caching member %d locally",member.memberId);
memberImg = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:member.imageUrl]]];
[[DataManager sharedManager] saveImageToDocuments:memberImg withId:memberId];
return memberImg;
} else {
return nil;
}
So the question is - is there any way of overriding the image compression even though the active network is 3G?
Thanks
There is no global mechanism that adaptively increases image compression for slow connections. What you describe would require custom code on the server, and would vary from server to server.
What service is providing these images?
EDIT: Thank you for fixing my answer, There are some mechanism of image compressing by Verizon network optimization.
I think,The quality of image, in the term of byte stream, depend on the server provide whether or not compression.
But there is some solution. you can also implement NSURLConnectionDataDelegate to handle the data from URL request with Thread Programming. There is interesting method :
/** connection:didReceiveResponse: is called when
* enough data has been read to construct an
* NSURLResponse object. In the event of a protocol
* which may return multiple responses (such as HTTP
* multipart/x-mixed-replace) the delegate should be
* prepared to inspect the new response and make
* itself ready for data callbacks as appropriate.
**/
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response;
/** connection:didReceiveData: is called with a single
* immutable NSData object to the delegate,
* representing the next portion of the data loaded
* from the connection. This is the only guaranteed
* for the delegate to receive the data from the
* resource load
**/
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data;
/** connection:willCacheResponse: gives the delegate
* an opportunity to inspect and modify the
* NSCachedURLResponse which will be cached by the
* loader if caching is enabled for the original
* NSURLRequest. Returning nil from this delegate
* will prevent the resource from being cached. Note
* that the -data method of the cached response may
* return an autoreleased in-memory copy of the true
* data, and should not be used as an alternative to
* receiving and accumulating the data through
* connection:didReceiveData
**/
- (NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse;
/** connectionDidFinishLoading: is called when all
* connection processing has completed successfully,
* before the delegate is released by the
* connection
**/
- (void)connectionDidFinishLoading:(NSURLConnection *)connection;
You can also manage your data in didReceiveData with accumulate each incoming data and when complete downloading , In connectionDidFinishLoading , you could deal with the NSData of image that you receive all.
Hope it helps you.
I am using NSURLRequest with CachePolicy to download a plist in NSData. When I change the content of my plist my app is ignoring this and still presents the content which is cached. How long does the cache persist? If so is there an option to say how long the cache data persists?
Is there a way to check in NSURLRequest if the data on the server is newer than the cache load the data from the server or if it is equal to cache use the cache?
Have a look at Controlling Response Caching in the URLLoadingSystem docs.
You can add your own date in the delegate methods
-(NSCachedURLResponse *)connection:(NSURLConnection *)connection
willCacheResponse:(NSCachedURLResponse *)cachedResponse
Much more easy with the caching system is ASIHTTPRequest. I recommend to use this URL Loading System.
From the apple docs:
The example in Listing 6 prevents the caching of https responses. It
also adds the current date to the user info dictionary for responses
that are cached.
-(NSCachedURLResponse *)connection:(NSURLConnection *)connection
willCacheResponse:(NSCachedURLResponse *)cachedResponse
{
NSCachedURLResponse *newCachedResponse = cachedResponse;
if ([[[[cachedResponse response] URL] scheme] isEqual:#"https"]) {
newCachedResponse = nil;
} else {
NSDictionary *newUserInfo;
newUserInfo = [NSDictionary dictionaryWithObject:[NSCalendarDate date]
forKey:#"Cached Date"];
newCachedResponse = [[[NSCachedURLResponse alloc]
initWithResponse:[cachedResponse response]
data:[cachedResponse data]
userInfo:newUserInfo
storagePolicy:[cachedResponse storagePolicy]]
autorelease];
}
return newCachedResponse;
}