I am new to iPhone development. I want to check whether the image is loaded in the image view and if the image view is nil then load the image. I want to implement this in cell for row at index path so that I can increase the scrolling performance of the table. How can I do that?
Luckily Apple provides a sample that does just this, LazyTableImages. You can move IconDownloader into your project and then change your TableViewController implementation to look like that of RootViewController
Related
I wanted to know how can we design the view controller such that.., the upper half of the screen remains fixed and the below part of the screen can be navigated through.. !!
Should we use slipScreenController here ?
Your description sounds nothing like the Appstore app but the Appstore app simply has one vertical UIScrollView and another horizontal UIScrollView inside that for images.
If you are referring to browsing categories in AppStore then:
That is a tableView implemented in such way that it doesn't take the whole screen area. You need to create a UIViewController (not UITableViewController) and than add a tableView to the view (using Interface Builder or code). That way you can change the size and position of the tableView and use the remaining area of the view for something else, for example a UISegmentedControl above the tableView.
If you are reffering to reading description and images of single app then I think that UIScrollView is used for displaying images, not sure about the rest.
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've been looking into creating a gallery mode in my application.
The functionality will be identical to the built in Photos App.
Here's the flow:
1. You touch on a thumbnail and ...
2. a modal view displays a large detail version of the image
3. You have the ability to scroll horizontally through all the images in the gallery while in this modal view
I'm stuck on step 3.
How do I dynamically load hi res images into a scroll view? I understand I need to set the contentSize for the the scrollView but how do I do that when I've only selected and loaded one image? What delegate methods do I need to implement and what does the heavy lifting look like?
Thanks in advance!
Refer to the following example project from apple, it shows how to use a scroll view to scroll horizontally through some views, u shouod only need to change the conents of those views to contain ur images http://developer.apple.com/iphone/library/iPad/index.html#samplecode/PageControl/Introduction/Intro.html
I have a horizontal UIScrollView that contains UIButtons (though it could be any object). I would like to only download images for these buttons as the user scrolls and they are seen. I would also like an activityindicator running on each button while the images are downloading. Here's what I've tried with results:
Check content offset of uiscrollview and download images for visible buttons. Problem: issues getting activity view shown within subclassed UIButton and not desired usability since images are only downloaded once scrolling stops.
Add subviews (not buttons) to the UIScrollview hoping to use the view's ViewController to initiate a downloaded on viewDidAppear. Problem: viewDidAppear never seems to get called (because I am using addSubView?).
I've seen other apps that do this kind of loading but need some guidance on the typical set-up. Ebay's app is a great example. All items have a default image until the item comes into view, then an activityindicator runs and the items unique image is downloaded.
Thanks for assistance.
Without actually trying it out, here's my idea:
You can use the UIScrollViewDelegate method scrollViewDidScroll: to find out when your scroll view finished scrolling and then use [UIScrollView contentOffset] to determine which part of the scroll view is visible and (CGRect)convertRect:(CGRect)rect fromView:(UIView *)view to determine the button's position within the visible part of the scroll view. Have a method that checks if the button has had its image loaded yet and if not, load it and refresh the view if necessary.
Most such apps are using a UITableView, not a plain scroll view. Joe Hewitt's Three20 framework has a TTImageView class that can do lazy image loading and is pretty well suited to this kind of use.
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.