I set the content of a UIWebView using loadHtmlString:. I don't add them to the UIView until they are need, but I need to know the max scroll height of each of them.
The problem is that UIWebView doesn't start loading it's data until it's added to a superView, and It's the delay of loading content that is causing this problem.
Question: Is it possible to force a UIWebView to load its content, without being added to a view?
You can add it to the view and set it's opacity to 0.01 to force the load. I've had to do this with MKMapView before.
I'd use hidden property of UIWebView - setting it to YES before view is added and clearing it to NO in webViewDidFinishLoad: should do the trick.
However, you comment to #logancautrell's answer is a bit unsettling - do you ever plan to get that many web views added to your views? I assume you know that, but just in case: depending on your possible HTML(5)/JavaScript/CSS code, you may observe severe performance hit even with a small number of web views for which iOS needs to allocate lots of resources.
If you plan to update your web views often, maybe you could benefit from UIWebView's stringByEvaluatingJavaScriptFromString: method? To some extent, the performance hit can be bearable, I think.
I suggest either pre-calculating the scroll heights somehow (not during web view load), or finding a way to display your UIViews without waiting for the scroll heights initially, and correct them later.
Related
I have some view inside wich there are an UIWebView. For performance reasons, I do not allocate the Web view on the fly, but it is set into IB and linked with a class outlet. When I do not need it, I set its hidden property to YES.
But, after having profiled my application because of performance problems, I noticed that when resizing the views containing those UIWebViews, they take a huge amount of time in :
[WebFrame(WebInternal) _drawRect:contentsOnly:]
So to prevent this, I also set their scalesPageToFit to NO, but this doesn't change anything.
I've tested deleting them from the project, and yes, the resize of the view is really much faster.
So how can I prevent the UIWebViews that are hidden to eat my process time in useless drawing work ?
Instead of hiding the UIWebView try removing it from the container view using removeFromSuperview. When you want to make it visible again add it back as a subview. This should keep the instance of the UIWebView in memory and prevent it from redrawing when it is not visible.
I have an application i'm currently developing for iOS which is suffering from some performance issues.
The app takes user input through a navigation controller with 5 views, the last view generates a view with a UIScrollView which has a paging effect.
Each page in this UIScrollView has 16 buttons arranged in a grid, each of these buttons is loaded with an image.
Unfortunately when I scroll to a new page in the UIScrollView, the app stumbles across in a jerky animation rather than a smooth one.
I was wondering if anyone had any suggestions on how to improve the performance for the paging UIScrollView effect.
Many thanks.
Is it smoother the second time you navigate to that view?
If so, it's probably the loading of the images that is taking the time. You can fix that by preloading your button images when the app first loads using [UIImage imageNames:...] in your app delegate. That way they will already be cached and available to render when the view is displayed.
If it's not faster the second time, it's probably the actual rendering of the views that is too slow. You can fix that by preloading the views themselves. If you store a reference to your scrollview's subviews in an array, you can preload those views in your app delegate and just keep them in memory ready to display whenever the scrollview is shown.
I doubt that those views will use up too much memory (probably a couple of MB, max), but if you are worried about it, just add a memory warning handler that flushes out the array and then re-create it next time it's needed.
I'm trying to lazy load UIWebViews inside a UIScrollView.
Every time the user scrolls, the WebViews frames are updated and new content SHOULD be loaded. And that's exactly where I'm having trouble. The repositioning works well, but the new content (local NSStrings, which are called using loadHTMLString) does not appear until I stop scrolling the ScrollView.
I've read this thread already: NSURLRequest won't fire while UIScrollView is scrolling.
Getting some inspiration from that, is there any association I could make between loadHTMLString and NSURLConnection? I know next to nothing about NSURLConnection.
If that's not possible, is there any other solution? Either halting the scroll for a while (like MobileRSS – an App Store app – does) or alternate loading methods?
Edit: My UIScrollView has paging enabled. So if I were to halt the scroll for a while, it should happen at every page. But I still don't know how to accomplish that.
Old question, but here is an answer for it.
You'll have to subclass the UIWebView and switch the run loops started at a overridden loadHTMLString:baseURL:
and switching it back after the html has been loaded (or failed to load).
Check out this project on github which gives you an example of where to override in all the right places.
I am working on an iPad app that lets the user scroll through a number of images (usually around 20 .jpg files in a single horizontal scroll view). The file sizes are around 200 kb each. The images are set as the "Background" property of a UIButton because I wanted to allow the user to click the button to save the image. Every time I run the app, it crashes after scrolling for a little while. If you don't scroll, it behaves normal. I did run the app using the performance tools and didn't find any leaks.
I am getting a "Level=1" memory warning just before the app crashes. I had it running with about 8 images in the scrollview and never had a problem. So I know it has something to do with the scrollView and the images/buttons. In the "viewDidLoad" method, I simply did the following to set up the scrollView and then linked it in Interface Builder:
[scrollView setContentSize:CGSizeMake(5722, 340)];
[scrollView setScrollEnabled:YES];
[scrollView setDelaysContentTouches:YES];
Any ideas on how to get this to work? I added the images directly to the button in Interface Builder. Would it help if I deleted the background image, and instead set the backgrounds in the "viewDidLoad" method? Any help would be appreciated.
Sounds like what you need to do is create individual cells that these images live on, that get recycled like you'd get in a tableview. I have some code which does this that you may use for your purpose, or at least give it a go anyway. Works just like a tableview.
It's available here. This does the heavy lifting for you already, in that all you need to do is create one of these, slap it in a view somewhere, and create your individual cells. Those cells will be reused as you scroll so you won't need more than N + 2 cells loaded into memory at any one time, where N is the number that fit on your screen.
as jer wrote, the problem seems to be in the recycling. Make sure to remove, release and update the content of each cell every time you get a new one in tableView:cellForRowAtIndexPath:
(I would have commented jer's post but I'm unable to do this, probably because of my limited permissions).
I am trying to implement a filmstrip-like UIScrollView that will be populated with thumbnails of catalog pages. Selecting a thumbnail image will cause the main UIScrollView to move to the selected page. The Catalog may contain 100 - 200 pages, and I want to load them lazily only when required.
I have done this in a UIScrollView with paging enabled, but haven't seen anything on the best way to do this in a non-paging scenario. There will be 6 thumbnails visible in the UIScrollView (+ 1 when the view is being scrolled) at any one time. I want to dequeue and reuse the thumbnail's UIView when the view is scrolled, as I am doing in the main UIScrollView (which is a paging scroll view).
Thanks -
Jk
I am also going to suggest you take a look at some sample code of Apple, that is, Photo Scroller. If you are a registered iOS developer, you should also take a look at the WWDC10 session about scroll views in iPhone applications.
http://developer.apple.com/library/ios/#samplecode/PhotoScroller/Listings/main_m.html
What you need to do is mimic the behavior of a table view (which is nothing more than a subclass of UIScrollView). What you should mimic is the reuse of the cells. It is pretty easy to implement and will dramatically reduce the memory foot print of your application since you only load the content that is currently visible in the scroll view.
I hope this helps.
Check out the scrollview suite sample code from apple. The tiled example can probably be repurposed very easily.
http://developer.apple.com/library/ios/#samplecode/ScrollViewSuite/
Check out this class..it may proove helpful..
VSScroller