I'm having a problem when scrolling down and up a tableView on iPhone it gets kind of stuck while loading the images i need a method to preload the images so the scroll can be fluid or load the images 'till the scroll event stops...
any help on this?
I found this article very helpful. It provides a very detailed example for lazy loading of images in the main runloop.
Lazy Table Images Sample Code included in iPhone Developer Resources. Check out Photo Locations Sample Code as well. It uses Core Data and "lazy loading" techniques if your image files are stored on the device.
Well, generally speaking, preloading images for table view is a bad idea. Think of a following situation: you have 100 cells, each containing one image. That means you'll have to load 100 images before showing the table, which will have a serious impact on avaliable memory.
The "loading effect" you're talking about can be caused by two things:
a) as you have said, the problem with loading images. If so, do it in another thread, and pass the image to main thread when it loads
b) You're using images that are bigger or smaller than the given size. This will result in resizing the image when it appears on screen, causing the ugly stop-effect - the solution is to draw images in size which is exactly the same as their size.
Chope this was helpful, Paul
Not sure about images, but with text I have downloaded JSON files when the view loads, parsed into an array and then loaded the tableview with that array.
Related
Can anybody tell me how to load or set images with high resolutions in UIScrollVIew .
I am getting memory warning and app is getting crashed without any stack trace.
Thank you in advanced.
I was also working on an app which had UIScrollView and had to request for High Resolution Images. The thing is, you should first check the size of the images being downloaded. Lets say, if the image size is more than 10MB, then it would be difficult for your app to survive with such a heavy load.
You can consider the following methodologies.
1.Download your images and compress them.
2.At a particular instance of time, there is no need to populate your Scroll Views array with all the images at once, instead try to have only three images,i.e
1.The current one which is being shown.
2.The previous one.
3.and the image next to the current one.
You can also take help from the link
http://www.raywenderlich.com/10518/how-to-use-uiscrollview-to-scroll-and-zoom-content
You should use the concept of lazy loading. As you said you used UIScrollView that's mean you have lot's of images and I guess you show them one by one or two or three at a time. Load only that images which are visible to the user. One more thing you have to maintain that is when user swipe to next image or next branch of images that's mean next image(s) that's are going to visible to the user. At that time before load the new images release all the previously loaded images from memory. I hope it'll solve your problem.
If you are trying to create multiple UIImageView of high resolution image inside UIScrollView, then it will create memory warning and application will crash.
I will suggest you to try reusable UIImageView , like create 3 UIImageView and replace images in it.
Try circular scrollview.link or UICollectionView
I would like to create a PhotoViewer for an iPhone.
For that, I already created a ScrollView with Paging enabled in that I add programmically add the UIImageViews. The problem I see is, that if I would have like 100 Images and I would all add to the ScrollView it would take alot of performance and memory.
How would you make it more performant? I thought about loading the Images of the following 2 pages and releasing the Images after the 2 Images before when scrolling through the pages.
I thought about creating a Subclass of UIScrollView and to name it UIPhotoScroller (or something like that). But I also want to show a UIView in the MainWindow with Information about the Images. Is it possible to make the UIView visible from the Subclass?
You really would help me with that. Thank you in advance :D
Create an NSCache.
When you need a particular image, try to get it from the cache. If it's not there, load it from disk and save it in the cache. The filename is a suitable key.
When you get a memory warning, tell the cache to empty itself.
The cache will release some of its entries periodically, depending on how it's configured. This is a good thing, but you might want to adjust it to have a particular total memory size. Tweak its parameters until it behaves like you want it to. To see your memory usage, use Instruments.
How about doing a UITableView with a single photo per cell. When a cell is being request by the data source, you display a spinner and have a queued NSOperation load the image and refresh the row when done.
You can control the amount of concurrent ops with a NSQueue, so you have complete control on performace/responsiveness. You can then remove old cached images when low on memory/paging, etc.
There are solutions to horizontal UITableView if you need horizontal scrolling.
Have you looked at the three20 library? There's an example of creating a great Photos app-like viewer of photos, and it's pretty easy to work with the three20 library.
Hope this helps!
I have a scrolling grid of photos that looks and functions pretty much exactly like the photo picker on the iPhone. It is constructed from a UITableView that uses a custom UITableViewCell which displays a row of photos (very similar to how Three20 implements it).
It works great except that scrolling performance is poor. I'm already following most of the best practices for fast UITableView scrolling (à la Tweetie).
The images are all bundled with the app. I load them on the UI thread, on demand. I use UIImage's imageNamed: so that the images will be cached after they're first loaded. Once I've scrolled through the table view once, it scrolls very smoothly.
The problem is, the first time scrolling through the table view, scrolling is jittery. I've profiled the app and found that the majority of the time is spent loading the images from the file system. They are JPEG images, already sized correctly (small). I tried using PNG images instead, but performance doesn't improve very much.
The iPhone photo picker exhibits much better loading performance. I'm wondering if combining all the photos into a single image, which I load once and then split into smaller images would be faster. It certainly works in games, but I know that's really a totally different story. Has anyone had experience doing that?
Any other ideas for how I can improve performance?
Incidentally, I'm having a similar, albeit less, performance problem for another UITableView that just uses standard UITableViewCells with one image assigned to the imageView per row.
One thing to try could be pre-caching all the images when the view loads. Beyond that, perhaps loading the images in the background (even though it's loading from the filesystem and not the web). I haven't tried this myself, but perhaps you could use something like https://github.com/rs/SDWebImage and have the URLs point to the filesystem. Users might see some placeholder images at first, but then the UI wouldn't stutter while images are loading.
Setting the PagingEnabled property to off improves the scrolling performance.
I had a similar issue using a UITableView to display information parsed from an RSS Feed. I ran into scrolling performance issues when there was a significant amount of data. Though I'm still working on it I suspend the parsing when the table is being scrolled. It resumes when scrolling stops. I am not at my computer, but I believe I used tableViewDidScroll and tableViewDidEndDecelerating. You can check these tableview delegates. In any case it works very well, I just need a more elegant way to pause my parsing.
Fantastic. That does work like a charm! So efficiently I ended up using insertRowAtIndexPath rather that reloading the table. Now it behaves the way it
Thanks so much!
Joe
I have around 20 tableview cells that each contain a number (2-5) thumbnail sized pictures (they are VERY small Facebook profile pictures, ex. http://profile.ak.fbcdn.net/hprofile-ak-sf2p/hs254.snc3/23133_201668_2989_q.jpg). Each picture is an UIImageView added to the cell's contentview.
Scrolling performance is poor, and measuring the draw time I've found the UIImage rendering is the bottleneck.
I've researched/thought of some solutions but as I am new to iphone development I am not sure which strategy to pursue:
preload all the images and retrieve
them from disk instead of URL when
drawing cells (I'm not sure if cell
drawing will still be slow, so I want
to hold off on the time investment
here)
Have the cells display a placeholder
image from disk, while the picture is
asynchronously loaded (this seems to
be the best solution, but I'm
currently not sure exactly how to do
best do this)
There's the fast drawing
recommendation from Tweetie, but I
don't know that will have much affect
if it turns out my overhead is in network loading
(http://blog.atebits.com/2008/12/fast-scrolling-in-tweetie-with-uitableview/)
Thoughts/implementation advice? Thanks!
Suggest you do a search in the XCode help docs for LazyTableImages. It's a sample app provided by Apple that asynchronously loads images into a table cell. It should be a good starting point.
You'll probably want to add a local cache to save the images so you don't have to keep downloading them each time, and a way to prune out old images out of the cache.
I have some 50 custom cells in my UITableView. I want to display an image and a label in the cells where I get the images from URLs.
I want to do a lazy load of images so the UI does not freeze up while the images are being loaded. I tried getting the images in separate threads but I have to load each image every time a cell becomes visible again (Otherwise reuse of cells shows old images)
Apps like Facebook load images only for cells currently visible and once the images are loaded, they are not loaded again. Can someone please tell me how to duplicate this behavior.
Thanks.
Edit
Trying to cache images in an NSMutableDictionary object creates problems when the user scrolls fast. I am getting images only when scrolling completely stops and clearing out the cache on memory warning. But the app invariably gets a memory warning (due to size of images being cached) and clears the cache before reloading. If scrolling is very fast, it crashes.
Any other suggestions are welcome
Loading the images on a background thread is still a good idea. If you didn't want to reload them each time, I'd suggest setting up an NSMutableDictionary and storing the images in there. You could use some unique identifier, like the row ID or even the name of the image, as the key for each image.
When loading a cell, you'd send an objectForKey: message to the NSMutableDictionary to retrieve the image for that particular cell (based on your unique key for it). If it returns nil, that means that the image is missing from the cache and you need your background image loading thread to go retrieve it. Otherwise, you will get back the appropriate image for your table cell to display. On a memory warning, you could clear out this cache of images with no adverse effects (aside from forcing them to be reloaded again on demand).
I have just successfully tackled the same problem by using a custom NSOperation to load the images in a queing fasion and stored them into a static NSMutableDictionary as a cache. Below is a link to the basis of the code I used to solve the problem.
Loading remote images for UITableViewCell
Best to read all the threads in the forum to help you understand what's actually going on.
lostInTransit,
I am having a similar problem and while exploring the many different possible solutions I found this blog post:
davidgolightly.blogspot.com/2009/02/asynchronous-image-caching-with-iphone.html
I would also suggest that you download the URLCache sample from the apple developer website:
developer.apple.com/iphone/prerelease/library/samplecode/URLCache/
And here is another post on the problem:
www.markj.net/iphone-asynchronous-table-image/
I'd love you to share your findings as well.
Lazy loading is like synchronous type request.. means wait for respond
ego image button is solution for that..
ego image button is asynchronous type request..don't wait for respond..just display data at a time....
you can download folder from github....
add to your project...
in xib..at image view ,change class to ego image button...
make object of it in m file...
you can use.....
For those who are interested, and are lazy like me, I would like to suggest an open source (MIT license) implementation of lazy/cached network of UIImageView images: SDWebImage
UITableView with image caching and resizing/setting in background thread:
http://blog.slaunchaman.com/2011/08/12/gcd-example-updated-now-with-more-speed/
This is Tutorial about NSOperation with example that show how to Lazy load images in UITableViewCell