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.
Related
Can anyone point me towards an example or tutorial for this? I basically want to save images to the documents folder then have a table that contains them for user review later on.
I've got it working but only when I go and add each image to an array then generate the table with contents of said array first. Is there a quicker or more automated way to do this?
Here's a nice tutorial giving a project you could adapt:
http://www.raywenderlich.com/19788/how-to-use-nsoperations-and-nsoperationqueues
While it's actually about doing lazy loading and other image operations on a secondary thread (keeping your UI responsive) you may as well display images in a table this way to begin with.
The main modification you would make is to look for the locally stored image first, then go and do the network fetch if it is not available. A further refinement would be to check a timestamp stored with each local image and update from the web if a newer one was available.
That is correct, you prepare your datasource first (which is array of images), then you pass it to tableview and reload it. If you are working with lots of images, consider lazy loading.
Apple has an example on this.
I am wondering if anyone can offer any advice towards solving this problem.
I am building an app that uses a UIScrollView with paging enabled, with each page corresponding to downloaded and parsed XML data. Part of that XML data is a URL to an image.
Now, it would take forever to load an app that downloads the image for every XML entry and then push it to the respective UIScrollView page created on runtime with the rest of the XML data.
Is there a way to be able to detect which UIScrollView page you are on and then download the image as needed and still allow the rest of the data to download at runtime?
Try to read SDWebImage or Apple's LazyTableImages
Just as referenece, I solved it by adding all of the image views into an NSArray. Using the scroll view delegate, I was able to determine which page number I was on, and translated that page number to an integer that I used to access the appropriate uiimage view located within the array.
It seems to work great!
Might you offer a better solution?
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 table view with all cells having the UITableViewCellStyleSubtitle,
the images of all the cells are got from the server.
However, those images are not changed frequently.
Someone can show me how to improve the user experience? Each time, user scroll down the table, it seems that it goes online to check and download images again.
Or at least, show me some options that are available to achieve the goal.
Thanks,
The Three20 library has an ImageView subclass that accepts a URL to your remote image and uses the excellent TTURLRequest/Caching mechanism to fetch images. It maintains an in-memory and on-disk cache and will only download images if they are not cached or have expired. You can configure the default cache-expiration time or use a value from your HTTP response. If you use the TTTableViewController subclass and the appropriate TTTableItem subclass, you will get the appropriate image downloading behavior for free. However, it is not necessary to use every three component to do what you need. If you're integrating into existing code, you could create your own UITableViewCell subclass that uses a TTImageView instead of the standard UIImageView. Then, in your cell configuration methods, you can set a default placeholder image and a URL to load and it will pretty much take care of the rest. As a performance optimization, you should also implement the UIScrollView delegate methods in your tableview controller to suspend the TTURLRequestQueue during scrolling (take a look at the TTTableViewController to see how this is done).
You could try one of the following
Create an dictionary and cache all the fetched images in it using the image name as the key
Cache and reuse the entire UITableView cells in tableView:cellForRowAtIndexPath:
If it is just one image repeating load it one outside tableView:cellForRowAtIndexPath:
You write that the images change on a monthly basis - you could save the images to disk as they are used and just either check if the images have changed on the back burner or at a given daily interval redownload the images. Brian Chapados reply seems interesting .
Depending on your code there is probably a ton of other ways to improve image loading. Hope that helps...
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/