So in an iOS app I'm using a UINavigationController as the root view controller. I then push a few ViewControllers on the stack, let's call them A, B, C and D.
Now if I try to pop D from the stack, I sometimes * run into the following problem:
After calling popViewControllerAnimated, the view of the topmost view controller (D) remains. If I display the stack however, it is displayed correctly, i.e. A-B-C is displayed and D is gone. The pop method seems to do just what it's supposed to but the view does not reflect this.
I have tried various other approaches, (popToRootViewController, popToViewController) instead but the behaviour doesn't change (i.e. the stack is printed correctly but D's view remains). I have called setNeedsDisplay on all views that seem to make sense.
After popping D, I can still push and remove other view controllers. The stack reflects those changes, the view does not. Also, D's view remains responsive, i.e. it is not frozen and the app does behave correctly in the background. All views are very simple, there are no tabbed views or the like, just a couple of labels and buttons.
I have read a number of posts on SO and elsewhere about people having similar problems but none of the solutions seem to fit here. Does anyone have an idea why this happens?
*_ I haven't been able to figure out under which circumstances exactly. I first thought it was because I am popping D very soon after pushing it, but it also occasionally happens when there is more time between push and pop.
Only reason i can think of where this might happen is if you are not doing that in a main thread. If you are doing it after some network call, then do make sure you are going back to main thread. Sometimes, app won't crash if you do UI work on background thread but rather will behave like what you are seeing!
The problem seems to have been one of timing. As I mentioned, the push and pop operations (of D) sometimes do happen rather quickly after one another. Adding a delay of 2500 ms solved the problem. Adding 500 ms did not (always). Since neither is acceptable to me, I switched to a custom container view controller and therefore didn't spend a lot of time on figuring out what the minimum delay would be.
Just as sidenote: Changing from dispatch_async to dispatch_sync didn't have any effect. The delay seems to be necessary either way.
Thanks for everyone's help. I'm going to close this thread - if someone can provide a more complete answer as to why things are the way they are, please post it and I'll mark it as the correct answer then.
Related
I'm using Xcode 5.1.1
When i click the BACK button from ViewController 1 to ViewController 2, and when VC 1 appears the ImageView glitches for 1 second before going back to normal. I tried programming the segue with performSegueWithIdentifier but that didn't solve the issue. I tried using Modal's cross dissolve transition, cover vertical and partial cross but they don't help the glitch either. Only Flip Horizontal doesn't have the glitch but it wouldn't look good with my app. I'm currently using unwind segue to go from VC 2 to VC 1 but the VC 1 is glitching for 1 second. I tried regular modal but that creates worse problems. What do i do?
Well you should admit that "The UIImageView" is quite a generic assumption to figure out what your issue actually is. Just for pure diagnosis purpose I'd do the following checks:
Check the size of your UIImage you're assigning to the UIImageView. If the UIImage is too big the higher resolution might cause some rendering problem in the animations.
To have a proper check of what's going on you might want to run instruments adding "Time Profiler" to your tab. Performing either the pop or dismiss of your VC2 you should be able to figure out where the glitch comes from.
I know it's quite a generic answer but with the little info you provided don't think anyone might be able to help you more than that.
Hope this helps.
I am working on an ipad project whose UITabBarController (it's also the root) has 5 tabs.
The second tab is a tableview where there are quite rich UI elements.
The problem is that everytime I launch the app and click the second tab, I would be blocked for 0.3 second to show the viewcontroller. However, after the first time enter this tab, it only takes me 0.03 to enter this tab again.
So I thought the ViewDidLoad cost too much, because I do a lot addSubView or reloadData there. So I add
[libraryVC viewDidLoad];
[libraryVC viewWillAppear:YES];
[libraryVC viewDidAppear:YES];
in application:didFinishLaunchingWithOptions, I think if I do this view load stuff before user enter the second tab, then there will be no block.
However after I tested this approach, I found the cost was not be reduced. So I guess the time cost may be used in the view render when first show this viewcontroller. When the viewcontroller's view has been rendered before, then the following show will be fast. But I have no idea to solve this problem.
I think this problem is very common when the viewcontroller's view is really complicated, so does anyone has an idea of the approach to solve this problem? Or does anyone can give a detail description of the reason why the block happens?
Thanks for any help!
Perhaps multithreading the time intensive methods/calls is the solution you are looking for. If you search "ios grand central dispatch" on Google, some great resources will be available. Apple's Grand Central Dispatch reference is one of the better pieces of documentation they have.
In the output window, when I bring up an menu (subview) over the current view, but NOT covering the iAd... I also, just to be sure, Did a BringSubviewToFront (iAds);
However, it still issues the message in the output.
Worse, if I touch on the ad it won't activate it. I'm pretty sure this would result in not only my app getting rejected, but also in making zero from ads...
I have several different views that I pop up in this fashion, one of them seems to not have the problem... However, I haven't figured out any differences between them...
-Chert
Turns out I had some old code that created a controller for that view (now a sub-view), and It appears that it was getting confused with a view having a subview that is registered to another controller from the controller that it is registered in... Can't say that I blame it for getting confused! -Chert
Facing a really, really weird problem with an OpenGL View we are using in our app to perform some custom animations. As soon as the Open GL View is added into the project, all native View animations slow down. And by slow down I don't mean a drop in frame rate. The animations are stutter-free, except much much MUCH slower than normal (like someone enabled "Toggle Slow Animations" in the Simulator).
This is affecting only view transitions animations, for example:
a. transitionFromView
b. presentViewController (iOS6, or presentModalViewController on earlier)
While regular UIView Animations, CABasicAnimation etc proceed at the regular pace.
I haven't seen anything like this, and the results honestly have to be seen to be believed. :) But any idea what the problem could be (I'm not sure which piece of the code would help you debug, and I'm unfortunately not in a position to share screenshots or video)
It seems like the animation gets stuck while loading the OpenGL View, debug the
Lifecycle methods like loadView, viewWillLoad. The loadview, etc. happens within the
transition animation, maybe you can solve the slow animation by sending most of the loading
code in to a custom method which you call in viewdidload or viewdidappear.
It does not interrupt any other animation because thats a totally new action in the queue.
Hope this helps!
Found the solution accidentally several days later.
The problem turned out to be much sillier and unrelated. It so happens that if you have a UIView beginAnimation block that is not closed properly, future animations get all wonky. This faultily coded animation happened to be triggered at more or less the same time as the OpenGL view was being initialized, which led to my erroneous belief that the OpenGL View was at the root of this.
Thanks for the help!
I have always been a bit unclear on the type of tasks that should be assigned to viewDidLoad vs. viewWillAppear: in a UIViewController subclass.
e.g. I am doing an app where I have a UIViewController subclass hitting a server, getting data, feeding it to a view and then displaying that view. What are the pros and cons of doing this in viewDidLoad vs. viewWillAppear?
viewDidLoad is things you have to do once. viewWillAppear gets called every time the view appears. You should do things that you only have to do once in viewDidLoad - like setting your UILabel texts. However, you may want to modify a specific part of the view every time the user gets to view it, e.g. the iPod application scrolls the lyrics back to the top every time you go to the "Now Playing" view.
However, when you are loading things from a server, you also have to think about latency. If you pack all of your network communication into viewDidLoad or viewWillAppear, they will be executed before the user gets to see the view - possibly resulting a short freeze of your app. It may be good idea to first show the user an unpopulated view with an activity indicator of some sort. When you are done with your networking, which may take a second or two (or may even fail - who knows?), you can populate the view with your data. Good examples on how this could be done can be seen in various twitter clients. For example, when you view the author detail page in Twitterrific, the view only says "Loading..." until the network queries have completed.
It's important to note that using viewDidLoad for positioning is a bit risky and should be avoided since the bounds are not set. this may cause unexpected results (I had a variety of issues...)
This post describes quite well the different methods and what happens in each of them.
currently for one-time init and positioning I'm thinking of using viewDidAppear with a flag, if anyone has any other recommendation please let me know.
Initially used only ViewDidLoad with tableView. On testing with loss of Wifi, by setting device to airplane mode, realized that the table did not refresh with return of Wifi. In fact, there appears to be no way to refresh tableView on the device even by hitting the home button with background mode set to YES in -Info.plist.
My solution:
-(void) viewWillAppear: (BOOL) animated { [self.tableView reloadData];}
Depends, Do you need the data to be loaded each time you open the view? or only once?
Red : They don't require to change every time. Once they are loaded they stay as how they were.
Purple: They need to change over time or after you load each time. You don't want to see the same 3 suggested users to follow, it needs to be reloaded every time you come back to the screen. Their photos may get updated... you don't want to see a photo from 5 years ago...
viewDidLoad: Whatever processing you have that needs to be done once.
viewWilLAppear: Whatever processing that needs to change every time the page is loaded.
Labels, icons, button titles or most dataInputedByDeveloper usually don't change.
Names, photos, links, button status, lists (input Arrays for your tableViews or collectionView) or most dataInputedByUser usually do change.