I've a big issue with "scrollRectToVisible" method, part of UIScrollView class.
I've a view with 4 UIScrollView displayed from top to bottom, with paging in the width way :
I can browse in them (like the in the "pictures" app, but with 4 images on the same view)
i can resize the height of each of them
everything works fine
Now, I want to use "scrollRectToVisible" in order to "randomize" the pages displayed in each UIScrollView.
The problem is that :
this function work for only 1 or 2 UIScrollViews (even if I call this for the 4)
if I resize the UIScrollViews with a "random" size for each of them, most of the time, only the "highest" can make this function running
I can't really figure out a rationnal explanation why some of them are working, and the other not
btw, it seems that there is a link between the height of the UIScrollView and the fact that the method works or not.
I'm quite disapointed because... I just feel like it's a bug in the system... but maybe I missed something mandatory to make this method work on my 4 UIScrollView...
PS : i'm not mad, but i'm becoming crazy... lol
PS2 : i've also verified all the contentView, contentSize, frames of my UIScrollViews and content... I don't see any reason why it does not work correctly.... because the "normal" touch-scroll works pretty fine !
Thanks for any tips or help
Try this UIScrollView sample: Scrolling
This question is too vague and undocumented to really know what your problem is. What heights are we talking here? If you're going lower than like 20 pixels, you might be running into touch problems where the touch isn't getting sent to the right place. Please post some suspect code, or even setup code and try to ask more directed questions. I'm happy to update my answer as needed.
Related
Im having trouble loading pdf's in a UIWebView when inside a Scrollview with paging enabled and just can't get my head around it.
So i started with the paging sample code available at apple developer, once done that i loaded instead of a Label in the ViewController a UIWebView that loads the Pdf. and it did worked but with a lot of bugs with rotation and scaling on the device.
On iOS 5 scaling is simply not working it zooms but scrolls to top and doesn't allow me to move inside the UIWebView so when I move the only thing i do is move between the pages not inside the UIWebView.
And with iOS 4 it does let me move but has tons of trouble when rotating the device, it doesn't refresh the UIWebView inside to the new frame (even though i do change the frame on didRotate method), so i was wondering if there is another method to load the PDFs that is not a UIWebView that is compatible with zooming and rotating with the UIScrollView with Paging.
Or is there something I should consider when loading the UIWebView inside the UIScrollView? a feature i have to enable or something i am missing?
Because at the beginning I thought it was a bug on iOS 5 and that i was doing something wrong when rotating (which probably i am anyway) but i have several apps on my iPad with ios 5 that do the same but have absolutely no trouble.
I hope you can point me in the right direction.
Thanks in advance!
You should really be using CATiledLayer and CGPDFDocument for this kind of stuff.
There is an example that I found just now : Olive Toast's Blog
Its time consuming to wrap your head around these concepts, but its well worth it. I created a webView+scrollview combo for a pdf reader, which had to be junked and rewritten with CATiledLayer.
Doing it using webview in scrollview gobbles up a lot of resources, ending in a very bad UX
Edit: Apparently there is another post that has a better answer than mine (you may find this link useful)
I'm using core-plot in my iPhone app to display datas in plots from NSMutableArrays.
I display 10 values on the screen and I allowed horizontal scroll only like that I can see all the values when I'm scrolling.
I've got something like 100-200 values in total to load.
I use differents tabBars to handle my differents needs.
Everything works fine, but when I launch my app on the iPhone I have some monstrous laggs when scrolling. Something like 2 seconds after the graph move (on the simulator there is no laggs).
I reload graph when I shake the iPhone.
I work on a 3GS, and there is no other app running in background.
Did someone had and resolved something like that?
Do you need more info?
UITable (and UIScrollView) has a bug in which it causes it to call layoutSubviews on its parent. Check to make sure this isn't causing your trouble. If it is, you may be able to solve it by wrapping the table in another UIView. I do this routinely to avoid this problem.
Another thing that can cause really slow scrolling is a lot of masks, transparencies, etc in your cells. For this, you might try setting the views to rasterize, which means they'll draw themselves once into a buffer, rather than draw themselves every time.
I have different view controllers and i linked them using insertsubview
There are atleast three levels of subviews for every screen the users sees.
I havent tested it on device yet.
I want to know whether this causes any performance issues
Also, is using NavigationBarController pop and push views better than addsubview and remove from super view.
(I dont want the back functionality of NavigationBarController and want a custom header. That is why i didnt use NavigationBarController)
This is an interesting statement :
I haven't tested it on device yet.
My advice is simple :
Test it on a device.
Only you know what your app does - you can't possibly think we can answer your question with so little information! 3 doesn't seem a very big number but I don't know what each of those views is doing so maybe it's an issue, maybe not.
I'm trying to workaround a long-running bug in Apple's SDK here, but I can't see how to achieve it without huge amounts of code.
Here's the bug:
Create a view.
Put another view inside it, with an origin ANYTHING except (0,0).
Configure the subview to resize to fill
...then, at runtime:
4. Set the superview size to zero
5. Set the superview back to ANY non-zero size
BANG! Apple's SDK goes haywire, resets the origin of the subviews, loses all ability to tell up from down, etc. (seems like the programmer "Forgot" to include a variable to record what the spring/strut-size was before it went to 0).
I've heard this bug has existed in OS X for 5 years or so, and Apple still hasn't fixed it. What I would like is some way (any way!) of working around it, without re-writing Apple's entire springs/struts system and implementing it properly, without the bug. Unfortunately, I can't even find the original references to the OS X bug that someone showed me previously.
EDIT:
...I have a resizing "drawer" at the bottom of the screen that has to shrink to small height. The problem is subviews "collapsing" all down to origin 0 (amongst other things) at the drop of a hat (technically: they're reducing their origin.height, but not re-increasing it).
The best solution I have found is to limit your minimum window size so that none of your views can ever hit zero size.
EDIT: an hour later, the collapsing behaviour has returned, without me touching the source files. I'll use source-control to double-check, but I believe all that happened is I added other files to a different part of the view-hierarchy and re-built. Argh!
(what follows SEEMED to work, but is now failing again, in the same way)
Hmm. So, I had two UIVC's on one screen. Refactoring so that I only had one made the resizing bug vanish. It seems to be a bug in the UIVC layout code.
NB: I had the idea this might be a problem because I know Apple currently advises you to only have one UIVC on screen at once with iPhone, even though this means you have to ignore their MVC architecture for complex apps. So, technically, they warn you away from this. But, at the same time, I'm now unable to use the MVC stuff for this code.
The following worked (for my current example - may not be universal!).
HOW:
If you're adding any UITableViewController instances ... give up. You'll have to re-implement that class yourself
Find my subviews that were in UIVC instances, and change the extended class in the UIVC header from "UIViewController" to "NSObject"
Move all code from viewDidLoad to init (remembering that "init" has special rules about first few lines etc)
Replace the instantiation of that UIVC from "[[vc alloc] initWithNibName:nil bundle:nil]" with a plain "[[vc alloc] init]"
Another potential workaround (that works in my current situation):
The only View I have right now that MUST have a non-zero origin and MUST resize-to-fit is a UITableView.
Apple has a special feature of letting you put any view as a "table-header".
So ... I've taken all my other components, stuck them in a large view, and made that the table-header view.
The downside is that they now scroll off the top when you scroll the table, but it allows me to give the table a zero-origin, working around the SDK bug.
I'm solving a problem how to make tableviews work within three20's TTScrollView. I have a project which I want to rebuild using three20 library. There is one module which allows user to flip through set of "pages", which contains table showing some list of data.
My problem is that when I rebuilt this module to use three20's TTScrollView, tableviews inside the scrollview do not work anymore. In particular, it cannot be scrolled and cannot select an item, because all touches are intercepted by the scrollview. I'm getting mad about this and cannot figure out how to make it work.
I'm able to make work either tableview or scrollview but not both (means tableview intercepts vertical dragging, while scrollview horizontal). It worked fine with UIKit's UIScrollview, so there must be a way how to do this, but simply cannot figure out how.
Please help, I'm struggling with it yet couple of days now, but cannot get over.
thanks much for any hint.
Matthes,
Unfortunately not many people here at SO help out much with three20 questions for whatever reason. You may have better luck asking the three20 google group (search for that on google).
First guess though without trying it myself: try using three20's built in table items such as TTTableTextItem or TTTableImageItem ...in certain scenarios with three20, he has built in code to ignore everything you write except for his own built in controls (which might be the case here, not sure).
You can see examples of how he creates tables with this code in the TTCatalog example app that you can find via www.three20.info