I have a table which is made from custom UITableViewCells which contains downloaded images.
Ive found the app crashes after too many images are displayed. How can best stop this? I don't mind deleting the first images, but don't know of the best way to do it.
EDIT
How do I write the images to the device for caching?
Post your cellForRowAtIndexPath code. Sounds like you have a problem there. If you're certain you do not, then when you receive the memory warning, release any objects you do not need, and can easily be loaded again if required. These objects may be in other ViewControllers not on screen or ImageView objects already displayed.
Best we can do unless you post code.
Or read Apple's Memory Management Guide.
Related
In my app I have a bit where the user can take a photo and it get dropped into a list and the user could technically forever keep adding photos.
So what is the best way of saving, storing and loading the photos the user takes? Taking into account, there could be hundreds. Also, loading them all in at once might not be a smart idea as well, but say have a scroll view, scroll down, and when hitting the bottom it could load say 20 more and then another 20, etc.
Any help, much appreciated, thanks.
Just decide where you want to store the photos, built-in photo library or apps documents folder or both (I'd go with photo library for users's convenience in watching, deleting, synchronizing etc.). If you choose documents folder, don't forget to support deleting ... Disk space is the users problem.
If you choose only to store in photos library and want access the photos later from within the app, you have to save the urls of the saved images. This answer tells you how it works.
Loading the photos in scroll view will need some optimization, i.e. it wouldn't be a good idea to load all photos in memory, but only the visible ones. As another answer says, the re-use of cell in UITableView could be a solution, but I think, UITableView is for the typical iPhone table, adjusting and customizing it and its UITableViewCells isn't worth it, if the only reason is memory usage.
I'd go with UIScrollView and react upon the delegate's methods to load new content and drop old one. If you want a non-paging UIScrollView you should use scrollViewDidScroll , which is fired really often, so maybe there will be need for another optimization - test it. A paging UIScrollView seems to be easier to me. Just react on scrollViewDidEndDecelerating for loading and dropping content.
Hope that helps.
use tableview, it will load it manages the memory and jst visible rows are loaded into memory if u use dequecell method
read tableview more here
http://developer.apple.com/library/ios/#documentation/uikit/reference/UITableView_Class/Reference/Reference.html
I'm encountering a common TableView data reloading problem. I've read many questions on the same subject but the problem was never exactly the same as mine...
I have a navigation based application. In the RootViewController's viewDidLoad method I make a request in order to get JSON data (articles). When the connection has finished loading I create custom Article objects for each entry. The Article class has an initWithDictionnary method which initializes the attributes of the object and most importantly creates a request to download an image. When the connection has finished loading I set the image attribute of the Article object.
The goal is to initialize the cell.imageView.image property with the downloaded image. At that point, you may have guessed what the problem is about.
Images are downloaded after the cell image is rendered so it stays empty until the cell is reloaded (if it gets out of the screen and then back in for example).
I guess I should call reloadData at a certain time but I don't know when. Ideally I would call it when all the cells are loaded but it doesn't seem possible.
I've tried a bunch of crazy things like waiting for a cell to load and the try to reload the previous one but it didn't work.
By reading Q&A out here I learned about Apple's LazyTableImage sample code but I don't understand all of it so I'm not sure I should/could use it.
Please ask me if you need more details.
Thanks in advance for any help.
You have to load the images Asynchronously. Keep in mind that your table data should contain a field per row specifying if the image was loaded so that (if true) you can skip loading and just display cached images.
Look at this question first: Load images async
There are about 10 good Lazy Loading Image UITableView tutorials. Pick one.
You'll get the hang of it by reviewing the tutorials after a while. Stick with it, it's an important concept, not only for this project, but for the rest of your programming career.
Lazy Loading Image UITableView Tutorials that'll make you smarter!
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 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