I have a UITableView which displays fetched RSS dynamically, I have now customized the RSS to return the image name so that i can later on add a UIImageView to to every cell in the table which displays the image beside every cell, here is the code for adding the image
UIImageView *imageView = [[UIImageView alloc] init];
imageView.frame = CGRectMake(0, 0, 40, 40);
NSString *path = [NSString stringWithFormat:#"URL/%#",object.imageName]; //"object" is the returned Object from the RSS, so basically what i am doing is appending the image name to the path url.
NSURL *url = [NSURL URLWithString:path];
NSData *data = [NSData dataWithContentsOfURL:url];
imageView.image = [UIImage imageWithData:data];
[cell addSubview:imageView];
[cell bringSubviewToFront:imageView];
so when i run my app the app runs slowly and even stops for a small amount of time, the reason for that is that i am loading all RSS imaged directly in this line NSData *data = [NSData dataWithContentsOfURL:url];
any solution for this problem ?
Thank you in advance
i actually thought of fetching the images in a separate thread,
dispatch_queue_t fetchImage = dispatch_queue_create("Fetching Image", NULL);
dispatch_async(fetchImage, ^{
NSData *data = [NSData dataWithContentsOfURL:url];
});
dispatch_release(fetchImage);
but doing so wont allow me to use the variable "data" outside the queue.
any idea ?
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSString *path = [NSString stringWithFormat:#"URL/%#",object.imageName];
NSURL *url = [NSURL URLWithString:path];
NSData *data = [NSData dataWithContentsOfURL:url];
dispatch_async(dispatch_get_main_queue(), ^{
imageView.image = [UIImage imageWithData:data];
}); });
The method [NSData dataWithContentsOfURL:] is synchronous: whenever you call it, it blocks the current thread (which is almost certainly your app's main thread) for as long as it takes to complete. This is very bad. Aside from making the UI feel janky, there's a watchdog process that will kill unresponsive apps.
You really, really want to use asynchronous network calls. Read up on NSURLConnection, but know, also, that there are many articles and libraries and samples out there on this exact subject: loading images asynchronously for display in a table view. Start with, maybe, AFNetworking's category on UIImageView, or maybe a library like SDWebImage.
You should retrieve your data asynchronously ! May be the use of a Open Source libraries will help you:
AFNetworking
ASIHTTPRequest - not recommended
Or you can also use the NSURLConnection class with the asynchronous mode.
Related
How to implement lazy loading of image without using below link:
https://github.com/rs/SDWebImage
Note: I don't want to use any third party tool. I want to do from my side.
If you don't want to use any library (some are MIT or public domain licensed, so I think the only reason not to use them is that you want to learn how to build it yourself).
Here is how to do it with a simple and effective way:
1 : Put a temporary placeholder image in your imageView.
2 : Get your image in background thread.
2-a : If you want the cache feature, search for a cached image.
2-b : If no cache feature or no cached image, get your image from its source.
2-c : If cache feature, save the image to cache.
3 : In main thread show your image in the imageView.
Pseudo Code : (I wrote it on the go, it is not meant to run and it may have errors, sorry for that).
-(void) lazilyLoadImageFromURL :(NSURL *)url{
imageView.image = [UIImage imageNamed:#"Placeholder.png];
if([self cachedImageAvailableForURL:url){
imageView.image= [self cachedImageForURL:url];
}
else{
NSOperationQueue *queue = [NSOperationQueue mainQueue];
NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url];
[NSURLConnection sendAsynchronousRequest:urlRequest queue:queue completionHandler:^(NSURLResponse * resp, NSData *data, NSError *error)
{
dispatch_async(dispatch_get_main_queue(),^
{
if ( error == nil && data )
{
UIImage *urlImage = [[UIImage alloc] initWithData:data];
imageView.image = urlImage;
[self saveImageInCache:image forURL:url];
}
});
}];
}
}
-(BOOL) cachedImageAvailableForURL:(NSURL*):url{
// check if there is a saved cached image for this url
}
-(UIImage *) cachedImageForURL:(NSURL*):url{
// returns the cached image for that url
}
-(void) saveImageInCache:(UIImage*) image forURL:(NSURL*)url{
// saves the image in cache for the url
}
Of course, this is only ONE POSSIBLE WAY to do it. I tried to make it simple, but there are plenty better and more complicated ways to do it.
Try it:
NSURL *imageURL = [NSURL URLWithString:#"www...."];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
NSData *imageData = [NSData dataWithContentsOfURL:imageURL];
dispatch_async(dispatch_get_main_queue(), ^{
// Update the UI
self.imgVWprofile.image=[UIImage imageWithData:imageData];
});
});
i have one NSMutableArray with some image url's. The images have sizes between 12KB to 6MB. I use AsycImageView class and implement but when large images are downloading application get crashed, I gave 6*1024*1024 (6MB) for maxsize in that class, increase time interval 60.0 sec to 180.o sec, but there is no use. I'm getting an error "Received memory warning" and when app crash automatically connection remove from device, but in simulator there is no crash.
Use GCD for lazy loading.
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(queue, ^{
NSString *strURL = url here;
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:strURL]];
UIImage *image = nil;
if(data)
image = [UIImage imageWithData:data];
dispatch_sync(dispatch_get_main_queue(), ^{
//now use image in image View or anywhere according to your requirement.
if(image)
yourImgView = image
});
});
you can do this using multiThreading. Here is a code
- (UIImageView *)getImageFromURL:(NSDictionary *)dict
{
#ifdef DEBUG
NSLog(#"dict:%#", dict);
#endif
UIImageView *_cellImage = nil;
_cellImage = ((UIImageView *)[dict objectForKey:#"image"]);
NSString *strURL = [dict objectForKey:#"imageurl"]);
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:strURL]];
#ifdef DEBUG
NSLog(#"%i", data.length);
#endif
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *dataFilePath = [NSString stringWithFormat:#"%#.png", [documentsDirectory stringByAppendingPathComponent:[dict objectForKey:#"imageid"]]];
if (data) // i.e. file exist on the server
{
[data writeToFile:dataFilePath atomically:YES];
_cellImage.image = [UIImage imageWithContentsOfFile:dataFilePath];
}
else // otherwise show a default image.
{
_cellImage.image = [UIImage imageNamed:#"nouser.jpg"];
}
return _cellImage;
}
And call this method in cellForRowAtIndexPath like this:
NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:imageURL, #"imageurl", self.imgPhoto, #"image", imageid, #"imageid", nil];
[NSThread detachNewThreadSelector:#selector(getImageFromURL:) toTarget:self withObject:dict];
The code will start getting images in multiple threads and will save image locally to document folder. Also the image will not download again if already exists with the same name. Hope this helps
You could download image asynchronously using GCD. Use the following code,
__block NSData *imageData;
dispatch_queue_t myQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, NULL);
dispatch_async(myQueue, ^{
//load url image into NSData
imageData = [NSData dataWithContentsOfURL: your_image_URL];
if(imageData) {
dispatch_sync(dispatch_get_main_queue(), ^{
//convert data into image after completion
UIImage *img = [UIImage imageWithData:imageData];
//do what you want to do with your image
});
} else {
NSLog(#"image not found at %#", your_image_URL);
}
});
dispatch_release(myQueue);
For further info, see dispatch_queue_t
I would recommend a drop in replacement API SDWebImage it provides a category for UIImageVIew with support for remote images coming from the web. you can also have a placeholder image till the images are downloaded Asynchronously
. Its easy to use and saves a lot of work
You're problem seems to be more of a memory usage issue than it is a performance issue.
If you really want to download image asynchronously I would recommend you use The UIImageView category from AFNetworking which has been fully tested and is very well maintained.
However here you run into memory warnings on your device (which obviously holds much less memory than your simulator which runs on your Mac).
So I would use first the static analyzer:
to see if leaks are present and then run a Leaks Instrument to track it down.
Hope this helps.
I'm doing an app which downloads info via a request to a website, giving me back and HTML and parsing this data I obtain my app info. For downloading this data I'm using, using a url with all the parameters the request needs at the end.
NSData *data = [NSData dataWithContentsOfURL:url];
NSString* htmlString;
htmlString = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
[self parserHTML:htmlString]; // here I fill a NSArray with the info parsed
[self searchSomething:htmlString]; // continue filling the NSArray
...
The task for download the data and parser the HTML takes long time.
What can I do to make this faster? Grand Central Dispatch? If so, how can I use it, because I'm using this and it doesn't works, because the NSSArray is empty:
dispatch_queue_t downloadQueue = dispatch_queue_create("pharmacy downloader", NULL);
dispatch_async(downloadQueue, ^{
NSData *data = [NSData dataWithContentsOfURL:urlReal];
NSString* htmlString;
htmlString = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
[self parserHTML:htmlString]; // here I fill a NSArray with the info parsed
[self searchSomething:htmlString]; // continue filling the NSArray
});
dispatch_release(downloadQueue);
If I don't use GCD it works. What can be the problem??
Thanks for your help. I'm totally lost!!! :S
Use NSURLDownload or NSURLConnection instead.
For some sample code you may take a look at QuickLookDownloader
To create an UiImage with a image file, I use the code as below:
UIImage *aImage = [[UIImage imageNamed:#"demo.jpg"]autorelease];
If I want to create an UiImage with the URL http://example.com/demo.jpg, how to do that?
Thanks
UPDATE
This is a three step process. First you will create an NSURL object to hold the URL we are attempting to access. We will supply this URL to the NSData class method, +dataWithContentsOfURL: to obtain the image over the network as raw data, then use the +imageWithData: class method on UIImage to convert the data into an image.
NSURL *imageURL = [NSURL URLWithString:#"http://example.com/demo.jpg"];
NSData *imageData = [NSData dataWithContentsOfURL:imageURL];
UIImage *image = [UIImage imageWithData:imageData];
Please note that +dataWithContentsOfURL: executes a synchronous network request. If you run this on the main thread, it will block the UI until the image data is received from the network. Best practice is to run any network code on a background thread. If you're targeting OS 4.0+ you could do something like this...
NSURL *imageURL = [NSURL URLWithString:#"http://example.com/demo.jpg"];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
NSData *imageData = [NSData dataWithContentsOfURL:imageURL];
dispatch_async(dispatch_get_main_queue(), ^{
// Update the UI
self.imageView.image = [UIImage imageWithData:imageData];
});
});
Here's what the same code might look like in Swift:
let image_url = NSURL("http://i.imgur.com/3yY2qdu.jpg")
let priority = DISPATCH_QUEUE_PRIORITY_DEFAULT
dispatch_async(dispatch_get_global_queue(priority, 0)) {
// do some task
let image_data = NSData(contentsOfURL: image_url!)
dispatch_async(dispatch_get_main_queue()) {
// update some UI
let image = UIImage(data: image_data!)
self.imageView.image = image
}
}
For anyone looking to load image from the web the following library may be helpful:
https://github.com/rs/SDWebImage
It's a UIImageView category which handles async loading and image caching from url.
fairly new to Objective-C and iOS development (coming from PHP) and I have a relatively simple question that I can't seem to find an answer to:
I am following along with an example for split View design where a web page is loaded into the Detail View when a user clicks an item in the master view. I got all this working, but would like to substitute web view for an image. So I've amended the app to load a UIImage instead of a WebView. What I'm looking for is the equivalent to this code:
NSString *urlString = [pagesAddress objectAtIndex:indexPath.row];
NSURL *url = [NSURL URLWithString:urlString];
// these 2 is where I get lost with the images.
NSURLRequest = *request = [NSURLRequest requestWithURL:url];
[detailViewController.webView loadRequest:request];
I came up with this:
NSString *imageName = [pagesAddress objectAtIndex:indexPath.row];
UIImage *myImage = [UIImage imageNamed:imageName];
// missing the last 2 calls: one to tell Xcode that it's an image "request" I want and the second to load the actual image (based on it's name that is already in an array) into the ImageView.
Thanks.
PS
I tried this:
NSString *imageName = [pagesAddress objectAtIndex:indexPath .row];
[detailViewController.imageView setImage:[UIImage imageNamed:imageName]];
And it shows just the first image, then crashes when I try to show the last one.
In the end, the solution were those 2 lines when I amended the code:
NSString *imageName = [pagesAddress objectAtIndex:indexPath.row];
[detailViewController.imageView setImage:[UIImage imageNamed:imageName]];
Notice that I had to change the setImage to convert the NSString to a UIImage or Xcode would complain. It turns out it was crashing because in the array where I had the image names, I had put 3 images into one entry (basically I forgot the commas!) so it was out of range.
Tim:
This line you gave me
UIImageView *imageView = [[UIImageView alloc] initWithFrame:self.view.bounds];
is unnecessary because I already have a view created, it would create another view which I never used. Also, replacing it with CGRect seems overkill if I already have a UIImage placeholder no?
In any case, it works now and I'm very grateful for all the help. iPad development with Objectve-C is a very thorny road and I expect I'll be bugging you guys some more.
Cheers.
Try this:
UIImage *myImage = [[UIImage alloc] initWithData:[NSData dataWithConentsOfURL:[NSURL URLWithString:urlString];
// don't know if you already got the following?
UIImageView *imageView = [[UIImageView alloc] initWithFrame:self.view.bounds];
[imageView setImage:myImage];
[self.view addSubview:imageView];
The first line is synchronous (= blocking), so in production, you should rather use - [NSURLRequest start] for this (but that's a bit more complicated).
Or use this for your local images:
UIImage *myImage = [UIImage imageNamed:imageName];
// Now, follow the same steps as in the first code-example, just skip the first line.
Try this (on iOS 4.0 and later):
// Execute a block of code on a background thread.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
^(void)
{
NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
UIImage* image = [UIImage imageWithData:[NSData dataWithContentsOfURL:url]];
// When IO is done and image created, set it on the main thread.
dispatch_async(dispatch_get_main_queue(),
^(void)
{
imageView.image = image;
});
[pool release];
});