I have few questions regarding loading images to tableviews;
I am using ASIHTTPRequest.
1.) I have a tableview, and i need to load images to it. I have images which has the size of 100KB, 180KB, 450KB, and 2MB. I know that these images are too big, but i have no control over this. I am forced to load these images in the tableview. When i do this, it slows the scrolling, and slows to switch from views to views. So how can i prevent this ? any solution?
2.) Presently i am using SDWebImage, i am not satisfied with this library because it slows the scrolling etc (even when i use images which is less than 110kb) I need a library that can perform faster actions ?
You may have to downsample the image to the image view size in the background before displaying it. It will definitely cost you a lot of CPU cycles upfront, but will speed up scrolling. I recommend the ImageIO framework because it has no issues running in non-main threads.
I don't think it's SDWebImage that is slowing your scrolling down. SDWebImage downloads the image in a separate thread, the only thing it really does on the main thread is place the image in the UIImageView and this has to be done on the main thread. I use SDWebImage in a few different UITableViewCells and I have been able to achieve smooth scrolling.
2mb is really large -- you are not going to be able to load that image into a UITableViewCell without seeing some jerk. The fact is that it takes some time for the UIImageView to render that image.
If I were you I would run your app through the Time Profiler instrument and see if you can figure out which lines of code are taking the longest to run in your UITableView or your UITableViewCells.
Related
I currently made an app which contains a tableview with 1000 cells. Each cell contains on the left side a UIImageview in the contentview. All the image files are currently stored in the NSBundle. Unfortunately the app is to big in size to download over 3g (one of the regelations from Apple) and I will need to cache these images.
I currently am downloading and saving each image once the cell is on the view (dereusable cell) but this slows down the scrolling drastically. Is their a way to keep the scrolling fast but once the user stops at a certain position it caches those files? I tried an NSOperationQueue but this did'nt work out for me.
Some hints in the right direction would be appreciated!
Thanks!
Well if you are the same downloading and displaying a table view, it's normal that you have a performance drop in the fps you get from your tableview as the cpu is using some of it's threads to download the data...
The only way you could gain in performance is if you speed up the drawing of your tableview cells by using core graphics to draw directly into the cell (as Loren Brichter demonstrated with the tweetie app).
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
So I've seen this question asked before and in fact I asked it last night but I thought I'd give it another go just to see if I could get any other unique views on the problem.
The Problem — I have an app with a large number of uiimageviews (with image downloaded to disk) in a scrollview which of course has two large problems facing it: Memory use, and performance. In my app memory use isn't so much a problem because I am employing techniques such as dequeuing and reusing imageviews and such. But performance is another thing entirely. Right now, as a memory saving procedure, I only store image filepaths in memory because it would be ridiculous to store images in memory. But the problem with this is that reading from the disk takes more time than from memory and slows down scrolling on the scrollview immensely.
So, what kind of techniques do any of you suggest for something like this? I've seen three20 but don't want to use it because I need high customizability in my view and that just won't do. Image files are not large, but just thumbnail size so there is no scaling or excess size. There's got to be an intuitive way to handle this. The built in photos app handles up to thousands of photos perfectly with low memory and slick and smooth scrolling performance.
Fundamentally, the problem is that you're probably doing a bunch of disk I/O on your UI thread, which is basically guaranteed to cause performance problems.
You should consider loading your images on a background thread and updating the image views on the main thread when the images are loaded. Depending on your use case you can get more or less clever about how far you preload in advance, etc, so you can have images ready. (There might be some usable source code or even Apple sample code out there that does something like this, but I don't know of it off the top of my head.)
You may notice that some applications (not sure about the Photos app) have an intermediate stage where they load a very small thumb size image for all images, and scale it up to the render size, which acts as a placeholder until the full size version is loaded-- if the user scrolls past that image before the full size is loaded, the visible effect is nearly the same as if the image was there all along.
I've got an app I'm working on where we handle a LOT of images at once in a scrollview. (Here's how it looks, each blue block being in image on a scrollview expanding to the right: http://i.stack.imgur.com/o7lFx.png) So to be able to handle the large strain doing this puts on memory. So I've implemented a bunch of techniques such as reusing imageviews etc which have all worked quite successfully in keeping my memory usage down. Another thing I do is instead of keeping the actual image in memory (which I of course couldn't do for all of them because that would run out of memory very quickly) I only keep the image's filepath in memory and then read the image when the user scrolls to an area of the scroll view near that image. However, although this is memory efficient, it's causing a LOT of lag in the scrollview because of the fact that it has to constantly read images from the disk. I can't think of a good solution on how to fix this. Basically right now the app draws to the screen only the visible uiimageviews and while the user scrolls the app will look to see if it can dequeue another imageview so it doesn't have to allocate another one and at that point it reads the image into memory, but as I said it's causing the scrolling action to be very slow. Any ideas on a strategy to use to fix this? Does anyone know what the native photos app does to handle this kind of thing? Thanks so much!
I can suggest you a simple solution to balance both the memory and the computer processing. You only keep small images like thumbnails in memory and only keep about 20 of them. One project that I am doing, I keep 20 thumbnail images (100 x 100) recently accessed, which doesn't cost a lot of memory. I believe that it costs about 200 kb all the time but comparing to a general available memory. I think it is good enough.
It also depends on your use case : if user scroll really fast and you don't know when will they go. You can have even smaller images than the thumnail and when you show it on the UIImageView, you resize it to fit. When user stops scrolling for a while. You can start loading bigger images and then you have a nicer images. User may not even notice about the process
I don't think there is a solution that can be fast and using as less memory as possible. Because we have memory, maybe not big but have enough if we use it smartly.
Slow scrolling performance might mean that you're blocking the main thread while loading images. In that case, the scrolling animation won't continue until the images are loaded, which would indeed cause pretty choppy scrolling performance.
It would be better to lazily load requested images in the background, while the main thread continues to handle the scrolling animation. A library that provides this functionality (among other things) is the 'three20' library. See the Tidbits document, and scroll down to the bottom where the 'TTImageView' class is described.
I had a similar issue with a PDF viewer, The recommended way to do this is to have as low a res image as you can get away with and if you are allowing the user to blow the image up/zoom, then have two versions or three versions of that image increasing the res as you go.
Put as much code as you can get away with in the didDecelerate method (like loading in higher res images like vodkhang talks about), rather than processing loads in didScroll. Recycle Views out of scope as you have said. and beware of autoreleased Context based Image Creation functions.
Load images in on background threads intelligently (based on the scrollView Offset position and zoom level), and think about using CALayer/Tiled Layer drawing for larger images.
Three20 (an open source iOs lib) has a great Photo Viewer that can be subclassed, it has thumbnail navigation, large image paging, caching and gestures right out of the box.
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.