HI,
I am getting my images using JSON and I need to display image at a time when my app is running so please tell me how to use asynchronous method to load the images into the UIScrollView?
Thanks.
whether you use a UITableView or a UIScrollView, you will use the same pattern, its just that you have a bit more plumbing to do with the UIScrollView. I would say use the UITableView unless you want to roll your own multi-column image thumbnail picker.
With the UIScrollView, you will need to create your own virtual rows and columns and detect when the ScrollView has scrolled a new row or a new column into view. You will need to queue (remove) the images that have scrolled out of view, and then load the images that have come into view. All in all, this is not trivial code.
The UITableView does all this for you (rows only, no concept of columns)
Having said that.. here is a reference to using the NSOperation class to lazy load your images into a UITableView while giving the user a smooth experience..
UIImage in uitableViewcell slowdowns scrolling table
Related
I have a UITableView with images like photo album, images are loading with lazy loading. I want to load more images while scrolling to the bottom of the tableview or when the last row of the table view reached. How can I do this?
UITableView already does lazy loading for you. It will only ask for the visible cells. If you are taking about adding more images to the table while the user is scrolling, you can implement UIScrollViewDelegate methods to calculate the current scrolling position, and when the user reaches certain point, add more images to the NSMutableArray on your datasource.
Check this
http://developer.apple.com/library/ios/#samplecode/LazyTableImages/Introduction/Intro.html
and this Lazy load images in UITableView
You can use SDWebImage.
This library provides a category for UIImageVIew with support for remote images coming from the web.
It provides:
An UIImageView category adding web image and cache management to the Cocoa Touch framework
An asynchronous image downloader
An asynchronous memory + disk image caching with automatic cache expiration handling
A guarantee that the same URL won't be downloaded several times
A guarantee that bogus URLs won't be retried again and again
Performances!
i have photo gallery which loaded to scroll view vertically and i only want to load visible pages to avoid memory issues like table views did. Is there a way to do this? i am using core data to get images and there are more than 150+ images in it.
I used this: http://www.markj.net/iphone-asynchronous-table-image/ and I'd think it would help in your scenario as well
if you are using vertical only scroll you may use UITableView with custom UITableViewCell.
This way, you get the lazy load done.
I am new to iPhone development. I am parsing a xml and display the title, date, contents and image in the cell. Now the scrolling is not smooth, it is stuck.
How can I increase it? I have already applied lazy loading in another view, I am not able to apply in the new view. So how can I increase the scrolling performance? Can I check for any condition that if image is already loaded in the image view, so I can stop once again the loading of image view?
What I do to guarantee fast scrolling in a table is to subclass my own UITableViewCell where I implement all properties that I need.
Whenever that tablecell is initialized I draw the properties of the cell on the cell itself. So when you need an image on there, dont use an UIImageView, but just draw the image on the cell. Also all the text I need I just draw on there.
After a long stuggle finding out how to do all this, I also found a nice blog post about this.
http://blog.atebits.com/2008/12/fast-scrolling-in-tweetie-with-uitableview/
First of all, check if you're not resizing the images - that takes a lot of computing power, and will slow down the table for sure.
Second of all, check for view hierarchy - complicated view hierarchy means bad performance. Rembemer to use as much opaque views as possible, and when you're using non-opaque views don't make the cells too complex(by complex Apple means three or more custom views). If the views are too complex - use drawRect method for custom drawing of the content.
There's a great example on how to achieve this provided by Apple called AdvancedTableViewCell (here's a link), and there's a great tutorial by Apple about table view cells (another link).
I'm trying to get my UITableView to show cells with images placed on them (contained in a UIImageView overlaid). I'm wondering why when scrolling up and down, the images look like they're overlaid on top of one another.
What can I do in this case for the sake of memory management as well as to fix this issue?
Make sure that when you're dequeuing a reusable cell that you remove whatever image view was in the cell before you add the one for the current index path.
Alternatively, you can change the image property of the UIImageView.
I am displaying 200 thumb nail images of size 4kb to 12kb in UIScrollView programmatically by adding UIButton when i am debugging in device it takes time to load the view.. can there is some method to load quickly the thumb mages are store in disk.
Use lazy loading by only loading the ones you show at once in any given moment - or use a background thread to perform the loading while keeping the interface responsive.
If your layout allows, use a table view and a custom cell that holds several thumbnails. That way you can use the tableview controller's built in methods to manage the lazy loading. I'm pretty sure that is how Apple does the thumbnails in the photo library.