I'm making a simple rss reader for the iPhone. The feed (http://feeds.feedburner.com/foksuk/gLTI) contains a reference to images that I want to show in my TableView.
By default, as far as I understand, the iPhone only tries to load images when they are needed: it will only load the images for the rows that are displayed. Only when the user scrolls down, it will start loading the ones that need to be displayed. Right?
Now, since the images are downloaded from the web (they are not too large, but still), the scrolling of my TableView is stuttering. This is in the emulator, so on the device itself it will only be worse.
Luckily, this specific feed only lists the latest 12 entries of the blog. So I guess I should be able to first download an cache all the images, so they can be loaded from the memory, rather than from the URL.
What is the proper approach here?
I had the same problem, where my TableView would have to download each image before it displayed the cell. Like you say, it causes a big slowdown in the scrolling speed. What you need to do is download the images in the background and then insert them into the cell when they're finished downloading. This is how the app store app does it.
This post has all you need to know, including a class file you can use straight away:
http://www.markj.net/iphone-asynchronous-table-image/
Related
I created a Collection View for a app that showing photo specific by self app captured.
When showing the original photo it very slow e.g. the size of 5MB~10MB may be too large for showing.
Is there any way that I can get or even create the thumbnail for preview?
I tried for using C# standard way but the Image.Save( MemoryStream in MAUI is Windows platform only ...
First of all, I want to point out, that it is not a matter of choice.
Too big images will not be rendered, and you will see nothing but white space. (Learned that from testing it on Android.)
You can check this first:
https://learn.microsoft.com/en-us/dotnet/maui/user-interface/graphics/images?view=net-maui-7.0
I also use ImageSharp. (Despite the non-sense that happened recently, this is still a very good tool).
In any case, maybe it will be good to store the photo and the thumbnail separately, speaking of collection view, I do not think that it will perform well, if you need to mass-scale 5-10 MB photos. At least the devices I use cannot do this effectively.
I am newly in iOS development.I have to make an application for a car dealer in which i have to show different cars with different colors.Please tell me the best way because i have to fetch lots of images every time from the web server.How can i reduce the rendering time in fetching the images.
Please consider i am very new in ios development and need your help.
If you have any sample application please share it with me.
You can use DB to store images as BLOB and also fetch images only when there is update at server.
First, make sure you send images that are no larger than needed.
If you have a list view that shows pictures of the cars, have a webservice send you premade thumbnails that are (preferably) exactly the right size.
Second, Make sure the images are loaded separately from the data set.
The best place to do this, would be in the controllers for your UITableViewCell.
Just have your UITableViewCell start their own thread to download and display the image as soon as they come into view.
Third; caching.
Make sure you save local copies of the thumbnails, and make sure the Table View Cells search for local copies of the images, and load those instead of downloading them if they are already locally present.
you can do:-
use lazy loading
use paging
use predicates for searches
use fast enumeration
these things in general will keep your app smooth
If you are going to show images in UITableView then you can use lazy loading. It will load images only for the displayed rows and once image for any row index has been downloaded, it will not repeat downloading for that row index. So its faster and useful.
i am developing a app which contains feature like default photo browser in iphone. I done some what similar to that. but after loading some(near about 10-15) images from remote server,i am receiving memory warning.My requirement is loading image one by one. For this, on scroll view i am putting an images and increasing the contentSize of scroll view. it will work fine. but due to memory warning app quite.
Guys, any have any idea to approach for this feature which work similar to photo app without problem?
thanks in advance .
You're running out of memory because you're keeping the data for 10 or more images in memory at one time. You need to have more logic in your code that not only preloads and increases the scroll view's content size, but also removes UIImageViews from the scrollview (and thus from memory) as the user scrolls to newer stuff. (You can also save "evicted" images to the cache area on disk so if the users scrolls back you don't have to go to the server again.)
If you use a UITableView, it will request the images only when needed, and will automatically purge off-screen cells to save memory. It may not fit into the aesthetic for your application, though.
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