I receive and parse JSON from the internet in my app delegate. In JSON there are links to images that must be displayed in table cells (1 image per cell).
If i fetch images in cellForRowAtIndexPath method, it takes quite some time to load the whole view. I use this code in cellForRowAtIndexPath:
NSURL *url = [NSURL URLWithString:imageUrl];
NSData *data = [NSData dataWithContentsOfURL:url];
cell.imageView.image = [UIImage imageWithData:data];
How should i fetch these images without slowing down application launch (where should i put my code)?
I read a few things about NSOperation, is this the right way to go?
Tnx.
you can implement lazy loading
try this out
http://kshitizghimire.com.np/lazy-loading-custom-uitableviewcell/
or you can check apple's example
http://developer.apple.com/library/ios/#samplecode/LazyTableImages/Introduction/Intro.html#//apple_ref/doc/uid/DTS40009394
good luck
Create class to download the Images. After downloading the Image you can Implement a delegate method. In the Delegate method Reload the cell with corresponding images.
Related
I'm developing an iOS application consisting of a static sqlite database, series of tableviews and tab based detail view where the first view loaded in the detailview is a swipable imageView which loads a series of images.
I've got it working with this code where it looks for the image locally but I'd like to have it load the image from a URL or display a default image if no internet connection is available.
The images are named in the database as (for the example) image.jpg and I'd like all of them to load from the same URL directory (for the example) http://www.someurl.com/images/
Thank you
- (UIImage *) imageAtIndex:(NSUInteger)index {
Image *currentImage = (Image *) [self.images objectAtIndex:index];
NSString *path = [[NSBundle mainBundle] pathForResource:[NSString stringWithFormat:#"%#",[[currentImage filename] stringByDeletingPathExtension]] ofType:#"jpg"];
return [UIImage imageWithContentsOfFile:path];
}
The process for this is really very simple:
Try to download your image data using NSURLConnection
If successful, create a UIImage from the data
If either of the above fails, switch over to your placeholder/built-in image
Display the resulting image
I advise you have some sort of placeholder while the image is downloading, since that can take quite a while.
Don't bother with reachability; it's not 100% reliable, whereas actually trying the download is.
Avoid doing this on a background thread or queue. NSURLConnection is asynchronous out of the box to make this easier for you. There are a ton of third-party frameworks that try to simplify working with connections if you wish, though.
NSString *urlStr = [#"http://www.someurl.com/images/" stringByAppendingString:[currentImage filename]];
NSURL *url = [NSURL URLWithString:urlStr];
NSData *imageData = [NSData dataWithContentsOfURL:url];
UIImage *image = [[UIImage alloc] initWithData:data];
Or something like that...
If the image is large or the internet connection is slow, the NSData initialization might take some time. Consider getting the images data in a background thread, or use some existing framework for that like SDWebImage
In my app I have implemented a method to download a image from a URL and display it in a TableView cell. The code is working fine but I also need to implement two more functions,
1) a UIActivityIndicator to show that the image is being downloaded.
2) Check whether the image is already downloaded. Download only if the cell is empty.
Here is my code.
-(void) downloadImage
{
NSURL *url = [NSURL URLWithString:#"http://cdn.iphonehacks.com/wp-content/uploads/2012/09/iphone5-front-back.jpg"];
UIImage *image = [[UIImage alloc] initWithData: [NSData dataWithContentsOfURL:url]];
[dCellImageView setImage:image];
[image release];
}
Thanks.
Use [NSData dataWithContentsOfURL:URL options:NSDataReadingMapped error:&error]. It is a synchronized method. So probably start activityIndicator before sending the message, and check error, then stop activityIndicator. What do you mean by 'cell is empty'? Do you store image in disk or just memory. If former, use NSFileManager to check if file exists.
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
It'll show an indicator on the left of the status bar. You can also use MBProgressHUD if you like.
And if you want to check whether the image has downloaded already before downloading, you need to store a key in your Core Data or Property List.
I have to Implement a UITableView that should display all hosted photos. Load the photos synchronously and asynchronously in different tabs.
how to call images from url??
To load an image from a url:
NSData *imageData = [NSData dataWithContentsOfURL:yourURL];
UIImage *image = [UIImage imageWithData:imageData];
You can use GCD to perform the actions asynchronously. There's a good tutorial of almost exactly what you're trying to achieve here
You can used the Apple TableView Lazy Loading. They have sample codes that download images asynchonously to avoid freeze of UI. See link below
Apple LazyTableImages
I'm just a beginner to iphone development.
Recently i'm doing a project in which images need to be swiped. Could any one help me with it?
The images are stored in a server whose link is given.
I'm need it badly. So please help me
thank you
There are two ways.
You could either look at using a Paging Scroll View
Or, You could look at getting a series of UIImageViews with the correct images in each and then setting up a UISwipeGestureRecogniser for both directions. On the swipe's event handler you can adjust the x and y positions of the imageViews.
This is basic stuff. You should read some of the How-to's on Apple's developer website to help you with the base knowledge.
Edit:
Regarding the Internet images, the code can be adapted into the paging scroll view example:
NSString *path = #"http://merrimusings.mu.nu/archives/images/groundhog2.jpg";
NSURL *url = [NSURL URLWithString:path];
NSData *data = [NSData dataWithContentsOfURL:url];
UIImage *img = [[UIImage alloc] initWithData:data cache:NO];
Load the strings from an NSMutableArray instead and you're good to go!
Use Three20 photo Album. Your problem will be solved.
I am loading image with data in my table view. Images are coming from web. I created method to get image url in model class.Model class has Nsdictionary and objects.
But this images is slowing down scrolling .Here is my code
UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:#"%#",
[(Tweet *)[recentTweets objectAtIndex:indexPath.row]urlString]]]]];
cell.imageView.image = image;
Please tell Where I am going wrong?
Use lazy loading and do your own drawing. Try to understand the techniques on the sample projects I linked. These are the best ways to improve the performance of tables with images.
here is the methodology I use for loading images into a UITableView from a remote location:
in your .h file, declare a mutable dictionary for storing the images:
NSMutableDictionary *images;
initialize the dictionary in -init... or in -viewDidLoad
images = [[NSMutableDictionary alloc]init];
in the .m, tableView:cellForRowAtIndexPath:, see if the image exists in your dictionary for the indexPath
UIImage *img = [images objectForKey: indexPath];
if the image does exist, just set it.
if (img) cell.imageView.image = img;
if the image does NOT exist, set the cell's image to a temporary image...
if (!img) cell.imageView.image = [UIImage imageNamed:#"imageUnavailable.png"];
AND add that image to your dictionary so it doesnt try to refetch the image if you scroll off and back to that image before it loads...
[images setObject:[UIImage imageNamed:#"imageUnvailable.png"] forKey: indexPath];
then, in this same block, use an NSOperationQueue, and a custom NSOperation ( here is a reference - NSOperation and SetImage) to get your image and call back into your UITableViewController with that image.
in your callback, add your image to the dictionary (overwriting the temp image) and call [tableView reloadData]
this will give you a nice non blocking user experience.
The are a couple of ways how to do it. I had the best experience with a Queue for the HttpRequests, which I pause during the scrolling process.
I highly recommend this framework for that:
http://allseeing-i.com/ASIHTTPRequest/
I also implemented an image cache, which only loads the images if there weren't in the cache.
And the last tweak was to actually draw the images instead of using a high level uicomponent like the UIImageView
The number one reason your code is slow right now is because you're making a network call on the main thread. This blocks an UI from being updated and prevents the OS from handling events (such as taps).
As already suggested, I recommend ASIHTTPRequest. Combine asynchronous requests with an NSOperationQueue with a smaller concurrency count (say, 2) for the image requests, caching, and reloading the rows when images come in (on the main thread) (also only reloading the row if its currently visible). You can get a smooth scrolling table view.
I have an example of this on github here: https://github.com/subdigital/iphonedevcon-boston
It's in the Effective Network Programming project and includes a set of projects that progressively improve the experience.
Download the images before you load the tableView, and store them in an NSArray. Then when the cellForRowAtIndexPath method is called, show a loading image until the image is in the array.